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Foreword

This book stems from many years of discussion and tireless introduction of measurement and inspection technology to those in industry responsible for the control of product quality. It became clear that there are few outside of the quality profession who understand and appreciate the measurement process, its implications and its techniques. I hope that through the use of this primer there can be a better understanding of what it takes to “take a measurement”.

MEASUREMENT

By:

Richard G. Chitos

What is measurement?

By Richard G Chitos- Willrich Precision Instrument Company, Inc

Chapter 1

Measurement- (Latin mensura) A figure, extent or amount obtained.

We are surrounded by measurement.  Almost everything we do involves measurement of some kind.  We measure the distances we run, the mileage we reveal to work each morning, the ingredients of a cake, and the scores on our kid’s report cards.  Just because it’s not a manufactured product doesn’t mean that measurement is not taking place.  Sometimes we use perceptive measurements such as “Tom’s nose is too big for his face” or “Betty is surely built well”.  Whether you realize it you’ve taken measurement mentally.  Unlike the “2000-year-old man” I can’t say when all of this measurement got started.  It probably all began when man began.

You’ve heard some stories about how we arrived at some very popular units of measurement.  You know the stuff about the king’s foot being considered a standard measurement so “Presto!’ We get the standard foot.  Unfortunately, the standard holds up for only a particular king’s foot; obviously this proved to be a rather poor measurement standard. Some other standards have been, the width of a thumb for an inch, the distance from the nose to the outstretched arm as a value of a yard etc. It seems those many years ago there was quite a hang-up on various body parts.

Measurement came into its own when groups of men were needed to build things. A solidarity artisan making a piece of pottery dealt with his individual perception of the size or volume of his work. But when it came to using hundreds and sometimes thousands of workers for time periods that could last for a hundred years or more, measurement and standards became essential. Can you imagine building the pyramids, the Parthenon or the Great Wall of China without some hard and fast rules and regulations. Although individual design plate it’s role, individual standards could not be tolerated. Henry Ford heralded the modern production line and the interchangeability of parts, yet it is obvious that these concepts had to be understood by those master builders of old.

Thousands of years ago in Egypt units of measurement known as “cubits” were used. The cubit was based on the length of the forearm from the elbow to the tip of the middle finger. (Here’s that hang-up on body parts again). What is important is that standards are established. If a number of stones were needed two cubits by three cubits by two cubits, the first of these was made and designed as a standard, to which all others could be compared. Here we  have the birth of comparative measurements. A principle that has stayed with us for thousands of years. It’s clear in today’s world we can’t walk around dragging a bunch of standards behind us, but we can readily obtain and uses tools that have been compared to a standard somewhere.

Just as our culture, its drama art and architecture is based on the works and the thinking of those great masters in the distant past, so does our ability to make reliable and meaningful measurements have its beginnings way back when. Had Euclid, and Pythagoras been busy thinking other thoughts we would not be able to accomplish much today. The old adage says “if you can’t measure it you can’t make it”. Few, if any high schoolers, as they suffer through their geometry classes can appreciate the implication and application of what they are being taught. I can appreciate this better than most as I had to take the subject twice and it surely wasn’t because I was enamored with its principles.

Without measurement we can neither produce or progress. You certainly could not produce a toaster or an automobile, that has thousands of parts without knowing that “this will go into that.” The designers of whatever is being produced demand that their specifications are met so that the finished product meets their ideal of fit, form, and function. That is that it performs its intended job. When the various parts of an assembly are designed there is included very specific instructions as to the materials to be used, the processes required and the nominal sizes of features along with the tolerances applied to those features. Tolerances are the amounts that the features of the apart are allowed to deviate from the perfect or ideal. No process is so exact that in our attempt to manufacture parts that we can make them 100 percent perfect. Tolerances recognize that there is going to be variations. Tolerances allow for some variation that will still permit the product to function.

Measurements are critical to all products. It is clear that parts of the space shuttle require some very critical measurements be taken. However, to the maker of chewing gum the thickness of the gum may be equally important. Make the gum too thick and the pieces won’t fit in their intended package, too thin and they’ll rattle around in the package. Besides, government regulations require that packages of consumer goods meet the package weights indicated. Too thin a product could lower the package weight and be construed as consumer fraud. Making the product purposefully thicker leads us back to the package problem again, but also increases the cost of raw materials. Giving away just a few grams of product on each package, when one could possibly be producing billions of packages, could equate to hundreds of thousands of dollars of additional costs.

In the beginning…………………………………………………………………………………….

Every product starts with an idea. Some gizmo or widget is needed to fill a need. The burden of designing these gizmos and widgets is given to the design engineers who come up with the plans to build the product. We can think of their specifications as the laws that need to be followed to assure product performance. These laws could be likened to the laws created by our legislative branch of government (the congress and the senate) their laws (specifications) are transmitted to the executive branch (the president) in the hopes that they will be carried out as congress intended, just as our design engineers pass on their “laws” to production to carry out the requirements to produce the product. And just as in our government something is sure to go wrong in the process, there is a need for judges to define if the law of the land is being observed, so it is true that judged are required in industry. Quality inspectors confirm or deny that the desired design specifications have been met. The similarity stops, in that generally inspectors are not asked to interpret the laws necessarily but to pass in the adherence of them (although every seasoned inspection professional has certainly done his or her share of interpreting).

So, just as our forefathers created a system of checks and balances in our government similar checks and balances are used in industry. These checks and balances can often times be aborted by having those responsible for quality inspection reporting to supervisors in the production group. That is why supreme court justices are appointed for life. They needn’t fear that their decisions will affect their positions. Maybe this is a call for guaranteed job security for the inspection department?

More and better products have to be made in order to secure our standard of living and that of the rest of the world. Greater productivity and quality products will secure America’s position as a world leader. Metrology- The science of measurement can help us reach those goals.

Nominal- The basic size

Tolerance- The amount the feature is allowed to vary from the perfect or ideal

Gizmo- Gadget

Widget- An unnamed article considered for purposes of hypothetical example

If .001 is “one thousandths” then 10 of them have to be… you got it! “Ten thousandths”.

If we see the value .010” we know we are ten times greater than .001”

Moving right along, if we multiply ten times ten we get one hundred likewise .010” x 10 = .100” or “one hundred thousandths”.

If we double any of these values the rules remain the same, the value just doubles.

.001” x 2 = .002” – – “Two thousandths”

.010” x 2 = .020” – – “Twenty thousandths”
.100” x 2 = .200” – – “Two hundred thousandths”

Remember now that the third place after the decimal is the starting place. In one of our examples we had shown the fraction 7/16 to be .4375” hey, that’s a fourth place after the decimal. Now the rules change a bit.

The fourth place is expressed as the “tenths” position. Why? Because it is ten times smaller than the “thousandths” place. It is “one tenth of a thousandths”.

.0001” is 1” divided up 10,000 times.

.0001” is 1/10,000

.0001” is .001/10

.0001” x 10,000 = 1”

Five of these little buggers (.0005”) is expressed as “five- tenths of a thousandths”.

Getting back to our example .4375” is therefore expressed as “four hundred thirty-seven thousandths and five tenth thousandths”.

In shop talk in order to shorten this mouthful a bit the value is sometimes referred to as “four hundred thirty-seven thou and five tenths”.

Most of you may want to stop here for those who need to or who are just curious the trek continues.

There is a fifth, sixth, seventh, etc. place after the decimal. For our purposes we’ll deal with the 5th and 6th places, so expression of the value doesn’t become too cumbersome.

Let’s look at a real wild number. .437532”. All the rules for the first part of the number remain unchanged (.4375) what changes is the last part. Instead of deferring to the popularity of the “thousandths” position a new position reign supreme “the millionths position”. Which is the sixth position after the decimal place (.000001).

.000001 x 1,000,000 = 1”

.000001” = One millionth

Guess what? Ten of these are ten millionths .000010”. Getting back to expressing the value we say .437532” is “four hundred thirty-seven thousandths and thirty two millionths”. Quite a mouthful, but sometimes necessary. In some cases, the millionth or ten millionths place is referred to in scientific notation.

1 x 10-6 equals .000001” One millionth

2 x 10-6 equals .000002” Two millionths

1 x 10-5 equals .000010” Ten millionths

2 x 10-5 equals .000020” Twenty millionths

For the first example all you need to do is take 1 consider there is a decimal place assumed after the number (1.) then move the decimal, in this case six times.

Angles on Angles

Any circle can be broken into 360 parts (degree). No matter how big or small the circle, you can get the same number of pieces from a pie no matter how big or small it is, the only difference is the size of the slice’s changes. As you have heard each of these parts is called a degree. Now, just as we have seen before units of measurement can be broken into smaller and smaller units. Just as hours in the day can be broken into minutes so can degrees. There are 60 minutes in a degree which is a breeze to remember. The next step is to chop these minutes down even further. The next step down is seconds. There are 60 seconds in a minute. Not so tough?

If you sliced a pie every 90 degrees, you’d get 4 slices. Every 45 degrees and you’d have 8 slices (typical with pizza pies). Taking it further, half that or 22 degrees 30 minutes would yield you 16 slices. And so on until you could (if you slice very carefully) wind up with 1,296,000 slices each one being 1 second (360 degrees x 60 minutes x 60 seconds=1,296,000 seconds). An arc is a part of the periphery of a circle and looks like this – – – – – – –

So, when we refer to the parts of this circle we’ve been dissecting we call them “arcs”.  So, 90 degrees becomes 90 degrees of arc, and looks like this – – – – – –

45 degrees would be 45 degrees arc, and looks like this – – – – –

22 degrees, 30 minutes (22 and a half degrees) looks like this – – – – –

1 second of arc (the smallest we’ll ever deal with) could look like this – – – – –

Of course, the larger the circle the larger the arc. A circle going around the waist of the earth (the equator) is 25,000 miles around (periphery), and 1 second of arc would be approximately 102 feet.

How we arrived at this is fairly simple. (25,000 miles divided by 1,296,000 seconds=.0192 miles. There are 5280 feet in a mile so, 5280 x .092 = 101.8 feet).

Therefore, large circles have large arcs and small circles have smaller ones.

If you were driving a car up a steep incline the steeper the incline the steeper the incline the sooner you’d reach the top of the hill. That means for every degree increase in steepness greater heights are achieved. Here’s an example.

Therefore, a relationship exists between angles and linear measurement. If we shot an arrow at the moon and we were off in our aim by 1 second of arc we would miss it by more than a mile. (Boy, those little seconds can sure get in the way). 1 minute over an inch length has a rise of .000291”. The same 1 minute over 10 inches rises from a plane .002909” and over 1 foot the rise is .00341”.

I like to remember that 1 second has a rise of .000005” over 1 inch, this way it’s easy to multiply to get other values. Here’s one for you.

What’s the rise of 2 seconds of arc over 10 inches.

.000005” x 2 = .000010” x 10 = .0001” Approx.

It’s approximate because the value for 1 second is not exactly .000005” but really .00000484” (see chart) though not exact it sure is close enough for most applications.

As you can see in the chart the conversion goes both ways that is linear measurements can be readily changed into angular ones.

You may be thinking how is this done. Actually the conversions are done using trigonometry. Pages through define the process of conversion.

Ok, you’re ready, using the chart as a guide convert 15 seconds over 10 inches into linear measurement.

Next which is greater 22 degrees 15 minutes 10 seconds or 22 degrees 17 minutes 59 seconds?

Linear: Relating to, consisting of, a line: straight

Answers to questions page

• .000727”
• 22^ 17 59”

The manner in which these angles are expressed on a print is again similar to how we express time. Minutes are followed by a ’ and seconds by a ”. The change comes when we express degrees but then again another similarity exists this time between angular degrees and temperature degrees both are expressed using a bubble (o).

Putting this all together we can use the following example to get some practice.

15 o 7’ 42” is actually 15 degrees, 7 minutes, 42 seconds.

Recently there has been a trend to express parts of a degree in decimals. 45 degrees 30 minutes then becomes 45.500 degrees. We divided 30 minutes by 60 minutes and got .500

45 o 20’ would therefore become 45.3 o

45 o 59’ is the  45.98333 or almost 46 o

22 o 59’ 59” which is just a second shy of 23 degrees therefore 22.0031 o

If a full circle has 360 degrees then a semi-circle has 180 degrees. The supplement of an angle is the amount by which an arc or an angle falls short of 180 ^.

 SUPLLEMENTAL 40 Deg

Continuing along the same thought a complement is the amount by which an arc or an angle falls short of 90 ^.

Finally, angles can be right, acute, or obtuse. As per the following examples.

If you’re starting now to feel somewhat obtuse yourself, about angles it’s time to go on to the next chapter.

Accuracy, Resolution, Repeatability

I used to own one of those digital watches which told me the time of day to one tenth of a second. Then one day I realized it didn’t matter very much to me whether I was doing whatever I was doing at 3:15 or 3:15:1?42. So, I bought one of those European looking models that has a graduation every five minutes. I still tell time but not as closely as I used to.

Both watches are very accurate it’s just that with my current one I’ve got lousy resolution. Now I can tell that it’s approx. 3:15 give or take a minute or so. So, what’s suffered? Certainly not the accuracy but rather the resolution – that is the least significant digit that can be read, the digital watch had a LSD of .1 giving it as wristwatches go a high order of resolution. I’m measuring resolutions typically start of mechanical gages having resolutions of .001” (one thous) down to (.00001”) or lower. Don’t confuse resolution with accuracy. I could of course have a watch that resolves to .1 seconds but be “off” by hours. Accuracy is the difference read on the measuring device as it is? being compared to a standard. In the case of the watch the question is what time I do have as compared to the standard which is ticking away in Greenwich England, if it’s exactly the same time I’m accurate if I’m “off” some amount that’s my level of accuracy or inaccuracy – now I’m pretty sure my new watch is accurate but I’ve got a problem. It’s resolution is so coarse that I’ve no way of reading it. Determine how close or “off” I am from the standard.

Lesson #1- It doesn’t pay to have a lot of high accuracy in a gaging system if you’re no way of confirming it. By high resolution now just let’s say my watch is “off: by a full minute = what if I could better its resolution by placing grads on the face every 30 seconds. Now I’ve got lots of resolution, but the watch is still inaccurate. Because the resolution is better, I can see the inaccuracy better but it sure hasn’t helped make the time correct.

Lesson #2- Higher resolution doesn’t buy you much except higher resolution. Accuracy stands alone + hazed? Now what if I check the same watch every day + at the same time + one day it’s running a minute late and the next day it’s exactly on time. The problem we are then facing is one of repeatability. The watch that is a minute off but accurate can be set to the correct time and stay that way, but the one that fails to repeat leaves us with a problem which to reckon.

Lesson #3- I’d rather have a system that is off that I can reset than one that varies all over the place.

Lesson #4- You can never be more accurate than you are repeatable.

Metrology: Distance between two points

Millimeter: Thousands of a meter

Tenths – Micron = Millionth of a meter

Inch – Micron = Million of an inch

Microinch much smaller than micron

Tenth = 100 Microinch

Micron = .004 (HAIR)= .0001                 HAIR (.004)   = Microinch

                —————                             ——————

                  40                                              4000

1 Micron = 40 Millionths

7 Microns = 280 Millionths

.1 Micron = 4 Millionths

20 Microinches = 20 Millionths

4 Microinch = 1 Micron

2 Microinches = .5 Micron

Variable Gage Study

The number of operators (2 or 3) and the number of trials (2 or 3) may vary. Each operator measures 3 – 10 parts in random order for each trial. Data storage is optional. An option of tests are described:

1. Gage Repeatability and Reproducibility

Gage repeatability is the variation in measurements obtained when one operator uses the same gage for measuring identical characteristics of the same parts; reproducibility is the variation in the average of measurements made by different operators using the same gage when measuring identical characteristics of the same parts. For each trial, have each operator measure parts in random order. Repeat the cycle, with the parts measured in another random order, for the number of trials required.

2. Gage Accuracy

Gage accuracy is the difference between the observed average of measurements and the true average. Establishing the true average is best determined by measuring with the most accurate measuring equipment. Have one operator measure the same parts, using the gage being evaluated.

3. Gage Stability

Gage stability refers to the difference in the average of at least two sets of measurements obtained with the same gage on the same parts taken at different times. How gage stability is determined depends on how often the gage is used between normal calibrations. If a gage is used intermittently, then have the gage calibrated before and after each trial to determine the amount of calibration change. If a gage is used constantly, then conduct another gage R&R study.

4. Gage Linearity

Gage linearity is the difference in the accuracy values through the expected operating range. Conduct two accuracy studies, one at each end of the operating range.

TYPES OF GAGES

REVERSIBLE WIRE TYPE PLUG GAGES

A wire type plug gage is a plug gage comprising a gaging member of straight cylindrical section throughout its length held in a collect-type handle. This design is standard in the range above .030 to and including .760 inches. DU-WELL offers this type of gage up to 1.010. Sizes below .030 are available on requested note.

TAPERLOCK PLUG GAGE

A taperlock plug gage is a plug gage in which the gaging member has a taper shank, which is forced into a taper hole in the handle. This design is standard for plug gages in the range above .059 to and including 1.510 inches. DU-WELL offers taperlock gages in this range.

TRILOCK PLUG GAGE

A reversible or trilock plug gage is a plug gage in which three wedge-shaped locking prongs in the handle are engaged with corresponding locking grooves in the gaging member by means of a single through screw, thus providing a self-centering support with a positive lock.This design is standard for all plug gages in the range above 1.510 and including 8.010. DU-WELL shows up to 4.010 in the catalogue and will quote prices on larger sizes.

PROGRESSIVE SETTING DISCS

A master setting disc is a cylinder provided with insulating grips, used for setting comparators, snap gages, etc. There are three styles. Style 1 is a plain cylinder approximately twice the length of Style 3. The gagemakers’ tolerance is split plus-minus from the nominal size. Style 2 is two cylinders each approximately one-half the length of the cylinder in Style 1. Generally one cylinder is the “GO” master and the other the “NOT GO”. The gagemakers’ tolerance on the “GO” is minus and on the “NOT GO” it is plus. Style 3 is a plain cylinder approximately one half the length of Style 1. The gag makers’ tolerance is split plus-minus from the nominal size. The standard shows four designs – one for the range .105 to .365, one for .365 to 1.510, one for 1.510 to 2.510, and one for 2.510 to 8.010. DU-WELL lists size ranges for each of the three styles from .150 to 4.510, and will quote on sizes smaller and larger upon request.

PLAIN RING GAGES

A plain ring gage is an external gage of circular form employed for the size control of external diameters. In the smaller sizes it may consist of a gage body into which is pressed a bushing, the latter being accurately finished to size for gaging purposes. This design is optional in the range above .059 to and including .510 inches. Gages in sizes above 1.510 inches are flanged in order to eliminate unnecessary weight and to facilitate handling. An annular groove is provided in the periphery of the “NOT GO” ring gage as a means of identification.

SWIPE

(A lesson in Gage Repeatability and Reproducibility)

BY R.G. CHITOS

There used to be an old rule of thumb that if given a part’s total tolerance the gage selected to measure the part should have a resolution of 10% of the total part tolerance. Until recently no formal mention was made to this method. Today Gage R&R (Repeatability and Reproducibility) tolerances are  specified when ordering gaging inspection systems, as well as when applying these instruments to various production inspection tasks. The former method of purely relying on resolution made no provision for gage repeatability, gage accuracy or operator influence. Gage R&R methods and supporting formulas make an effort to resolve the issue by considering all of these variables.

The move to Gage R&R practice is welcome as it finally addresses some of the important areas that all good gaging practitioners have always known. The shortfall is that many of those who interpret the Gage R&R results do not fully understand the results. When specifying a 10% R&R, that is that the result of the test shows that the application of the specific gage tested does not consume more than 10% of the part’s total tolerance, many fail to realize that given standard practices and budgets 10% is not readily achievable. Many Inspection Managers will readily accept results of 20% of the tolerance and even 30% in some cases.

It is surprising how many companies have no idea what percentage of their total tolerance is being “eaten” by poor gages and poorer gaging practice. Routinely, when finally analyzed, gages and their application have consumed 50-60 and 100% of a parts tolerance.

The methods used to perform Gage R&R studies employ the use of several operators to take repeated readings on gaging masters as well as finished parts. The procedures allow for separation of operator reproducibility from gage error. This divides the blame, but in reality the gage supplier is generally saddled with the full brunt of the lack of adherence to the desired specification without regard to all of the variables that affect the final outcome. The very term GAGE R&R places the blame for whatever the problem directly on the gage.

SWIPE

Swipe is a mnemonic which stands for the following influencers of total measurement performance:

S- The Standard, is it certified and when, is it the proper class. For example in setting a bore gage to gage a 1” hole having a .00005” Bandwidth tolerance, if one were to use a class Y tolerance master, the uncertainty of the master alone could be as much as .0001” which is 20% of the total tolerance of the hole to begin with. The roundness of the master may be up to .00005” which is already 10% of the Gage R&R.

W- The Workpiece, every part varies, some more than others. Are the R&R operators aware of the variation within a part? Does the part have intrinsic taper, out of roundness conditions, surface finish variations etc. that can affect the measurements. Just by not taking measurements in the same place or zone on the part repeatedly can cause the R&R to suffer significantly. A .0001” out of roundness condition can consume 20% of the total part tolerance using the example above.

I- The Instrument itself obviously has linearity, and repeatability characteristics. Whatever they may be, clearly they add to the gaging uncertainty. In addition, certain instruments are more prone to operator loading, use, and care.

P- The Personnel and their ability to adapt the gage to the part is an ever important factor. Surely the gages vulnerability to operator influence can be considered the gage’s fault. However one should not discount the variation in touch and experiment that the operator brings to these tests. With some operators and their influence there may be no gages or inspection equipment made to perform the measuring task at hand. Surely an enigma, but best handled when best understood.

E- The Environment. Parts that are dirty, oily, or hot or even cold are poor candidates for R&R testing methods. They may represent the real world conditions but offer no stable ground on which to buyoff on a gages ability.

So there you have it, the SWIPE scenario. The answer may very well be that considering all of the variables, the only one that can be rectified is the gage’s intrinsic accuracy and repeatability. In this case it becomes necessary to obtain gages of a higher order. This may mean changing from Mechanically applied hand tools to Electronic or Air Gage tooling. These tools permit higher resolution and linearity and repeatability. They limit operator influence and offer output to SPC and signaling modules. The cost may increase but the value per item measured makes these types of tools irreplaceable.

Gage R&R, while an important measure in the measure of the measurement system requires careful consideration in its application.

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Equipment calibration has always been a necessary part of maintenance. Regardless of the type of gaging equipment, calibration is a must for the purpose of maintaining quality. The accuracy of measurements taken with gaging equipment can start to degrade over time due to wear and tear brought on by extreme temperatures and harsh conditions. Without regular calibration, it can result in parts being made with incorrect dimensions. This can lead to costly rejections and repairs, as well as a decrease in product quality.

The following points will further explain the reasons gage calibration is important.

Maintain Accuracy

Gaging equipment is used in the field of engineering and design for measuring parts. Using gage devices is essential to get dimensional information and determine whether a part or an object meets a standard or a system. As mentioned, the accuracy of a gage device can degrade over time. Hence, to ensure that it provides accurate readings and is performing its job correctly, regular calibration is a must. This process verifies and restores the accuracy of the gage as needed.

Quality Assurance

Poorly calibrated gage creates inefficiency and can significantly impact quality and safety. When there’s no accuracy, the rate of rejected parts will be high. On the other hand, accurate gaging devices improve product quality. Also, they help with quality control as they can quickly spot parts that do not meet standards earlier in production. It is important to calibrate devices in order to maintain the integrity of readings and the accuracy of measurements.

Compliance

OEMs these days are demanding suppliers and companies to establish calibration programs for their measuring equipment. According to ISO 9000, companies should continuously examine their programs for weaknesses and make improvements. Meanwhile, ISO 9002 states that suppliers must calibrate equipment and devices used for inspection, measuring, and testing at prescribed intervals against certified equipment. To help them stay compliant, some large companies hire specialists in calibration methods while others use calibration services.

Keep the Company’s Reputation

If a company doesn’t detect rejected or poor-quality parts, its customers soon will. These errors or inaccuracies can lead to costly consequences, including damaging a company’s reputation. To protect the company’s image, gage calibration is necessary.

Tips on Gage Calibration

How to choose the right calibration company? Take note of these tips:

• Ask for Certificates – When choosing a calibration house, make sure that they provide you with a certificate of calibration. This is important for compliance. The certificate must include the following information:
  • The serial number and description of the gaging equipment
  • The serial number of the gage used for the test
  • Tolerances of the data or level of uncertainty of the calibration
  • A statement of traceability to nationally recognized standard
  • The serial number of the NIST test where the house based its standards
  • Reference temperature
  • Date of calibration
  • Signature of the technician
  • Test results

The house must also indicate that the gage was adjusted or recalibrated in the certificate.

• Look for Documentation – ISO 9000 requires calibration houses to document their methods and procedures in a manual. You should ask about them before enlisting their services. If unavailable, find a different calibration house.
• Consider Reputation – To date, there haven’t been any standards for calibration houses. That’s why you must be extra cautious. Reputation can be a good starting point when choosing a company. Still, don’t be afraid to ask a lot of questions to gauge the company’s experience, expertise, and reliability.

A bore gage is an instrument used to determine the inside diameter (ID) of a hole, a cylinder, or any spherical object. Bore gages differ in measuring techniques. Although, a typical bore gage features anvils that expand until they touch the inner surface of the bore. Measuring bores is an essential step when assembling or building an engine. It is also done as part of equipment routine maintenance of equipment to check for wear-out parts.

Is There a Different Method for Measuring Small Bores?

For many years, our experts have tried air gaging as well as back pressure for measuring small bores that are below 1 mm. This method can be instrumental in taking measurements of small bores. However, it’s not the best tool as it provides details about flow area and, not form information. The problem with these bores in question is that they are too small. It is possible that there is no other economical way to measure small bores other than air gaging.

If the bore measures more than 1mm, then there will be various bore gages in the market to use. You will find gages that measure 1 mm – 20 mm bores.

Can You Use a Plug Gage for Measuring Small Bores?

The short answer is no. To get the bores’ sizes and deviations, this type of mechanical bore gages use comparison. However, they don’t work the way fixed plug gages do. They neither need a ground cylinder nor a sensitive contact when making a comparison of a master to a bore. Instead, they use the plug’s mechanical transfer as the only probe for measurement. Because centralizing plug is not present, the probe is rocked inside the bore. This way, it can measure its diameter.

In other words, a plug gage is used to check if the internal diameter of a bore falls within the specified tolerance. Meanwhile, a bore gage simply measures the size of a bore.

This method is actually similar to adjustable bore gage technique that many people are familiar with. However, the small-probe gage can take the measurement of bores that are significantly smaller as compared to the holes that an adjustable bore gage usually measures. The former gage can be used for different kinds of holes or parts. That means, a user doesn’t have to use different tools for their measuring tasks.

Although, one must take note that its measuring range is limited. A small-bore probe that has a 1 mm nominal size measures 0.95 mm – 1.15 mm bores. A probe with a 10 mm nominal size measures 9.4 mm – 10.6 mm bores. Lastly, a probe with a 20 mm nominal size measures 19.4 mm – 20.6 mm bores. Nevertheless, they have repeatability and a measuring range accuracy of 1%, which are great advantages.

How Does This Type of Probe Work?

As mentioned, a small-bore probe work like a fixed plug gage, but with a few differences. Its sensitive contacts change to determine the bore diameter. As they do that, the size is being measured which will be seen in its indicating device. Depending on the small-probe gage, the indicating device could be a digital indicator, a dial, a comparator, or an LVDT.

Like any gage, this small probe gage needs a setting master. The master should be placed on the probe and then rock the plug. While rocking it, the user shall observe the indicator readout until it reveals the smallest value or reversal point. Next, the user shall set it to zero. Sometimes, it is also set the point to nominal size. Only after these steps shall the user start measuring the bore to find its diameter.

Fortunately today, there are digital indicators that simplify the process, thanks to their advanced features. They now have a memory feature. That way, the user doesn’t have to keep remembering the smallest value while measuring bores. Thus, speeds up the entire process.

Small probe gages offer a precise way to measure bores ranging from 1 mm – 5 mm. They provide the users with the necessary information for tight tolerance bore measuring applications.

Introducing the Marameter 844 K Bore Gage System from Mahr Metrology

Marameter 844 K self-centering dial bore gage system is ideal for measuring bores ranging from 0.95mm – 1.55 mm. A self-centralizing gage is among the basic types of bore gages, which include the go/ no-go plug gages, indicating plug gages, and non-self-centralizing rocking gages.

Why use self-centering dial bore? Rocking the adjustable gage takes a lot of effort. The user has to develop the right skill through performing the method conscientiously. A poorly trained operator is likely to produce inaccurate measurements. The greatest benefit of this type of gage is that it eliminates the need of “rocking” to center the gage in the bore. It also avoids operator influences and doesn’t require a lot of training. A user can easily learn how to operate it.

Our Marameter 844 K self-centering dial bore gage system has been a part of the Marameter hole measuring system for many decades. It has been tried and tested and has undergone innovative upgrades for maximum linearity accuracy. You can use this for determining the diameter and testing the roundness and tonicity of bores. It can also be recommended for testing batches. Our product comes with a measuring holder 844 Kg, a probe, and an expanding pin. It is packaged in a quality wooden case.

For more than 50 years, Willrich Precision has been dedicated to bringing high-precision gear, measuring tools, and metrology products. Our team strives to ensure top quality products and services. We are an ISO:9001:2015 company that constantly is in the mission to help businesses streamline their measuring processes while taking their quality assurance to a new level.

Our company is a proud partner of Mahr Technology, a five-generation family business that operates globally. For high-quality measuring instruments from Mahr that you can use for analysis and evaluation of workpieces, visit our website. You can also contact us if you need quick and reliable support from our service experts.

One of the advantages of using air gages is that there is little contact between the tool and the workpiece. In fact, such tools are typically referred to as non-contact tools. But, strictly speaking, this is not entirely true. Air gage tools do come into contact with workpieces, and this may be reflected in the fact that they do suffer wear and tear over time. The progress of this degradation may be significantly slower than that of contact gages but eventually, it is bound to happen.

How Wear And Tear Leads To Centralization Issues

When your air gage tool is sufficiently worn out, the clearance between the workpiece and the gage will usually be greater than it was designed to be. This in turn leads to centralization problems where the air gage tools measure a chord of the workpiece in question rather than measure the diameter of the part. Centralization problems may also arise if the centerline of the jet is not aligned with the plug centerline. As the tool degrades and the space between the bore centerline and the chord increases, the centralization errors become bigger and bigger.

Obviously, machine operators will allow for some centralization error, but this depends on how much leeway their process allows them to. With looser tolerances, these kinds of errors don’t pose much of a problem. However, with tight and precise machining, this becomes a problem for the machine operator.

Understanding Balance Errors

Unlike centralization errors, balance errors happen when the orifices and cavities in the air gage jets become clogged or are damaged by misuse, or as we saw earlier, become worn-out unevenly. This is because for your air gage to work properly, it is important for all the jets to have the same orifice diameter and recess. Anything that changes these parameters throws your air gage tool off-track.

The next question then is how you can spot this wear and tear and what you can do about it. There are two main approaches that you can use to do this.

Visual Inspection

Though not always possible, you may be able to see contaminants that may be clogging up your jets. This will of course depend on the type of tool you are using, its size and so on. This is part of the reason it is essential to keep your gages as clean as possible, as well as the workspace that you use them in. However, visual inspection may not always be possible. Even in the circumstances that it is, it may not always be possible to understand just how badly the problem is affecting your measurements.

In order to get a more accurate picture of the problem, try the second approach.

Using A Master

This approach is based on the fact that for most air gage tools, wear and tear tend to follow a fairly predictable pattern. With gages that are hand-held, the wear is often around the plug’s circumference and tends to be relatively even. For these, secure the gage horizontally, then take a master reading. Having noted the reading, take the master and place it on the lower surface of the plug. Again, take another reading. If there is wear and tear of the plug, the readings will be different. Generally speaking, if the difference between the two is more than 10% above the acceptable tolerance, you may have to replace the plugs, or the tool all together.

Air straightness plugs are slightly more sophisticated than conventional air plugs, but still have all of the benefits of a normal air plug: they are simple to set up and operate, and they produce highly accurate results.

Design

A conventional air plug includes four measurement jets, two in the center and two at the ends, arranged in two groups. The plug’s structure enables it to see both ends of the bow situation. The exact location of the jets in relation to one other is not governed by any standards, as is the situation with squareness or taper tests. There are no ratios concerned, either.

The air nozzles at the plug’s extremes are designed to check for non-straightness, which is normally defined for the bore‘s whole length. However, before we can grasp the way in which a straightness plug functions, we must first look at the different combinations of jets that are common in air tooling.

Differential Measuring

A differential measurement system is what is associated with a two-jet plug. Picture a two-jet gas plug with a zero readout within a master ring. Adjust the plug such that one of the jets is positioned on the ring’s side. This raises posterior force on one jet while lowering it for the other.

A four-jet system is an expansion of the two-jet gas plug. Four jets are combined together in this case, and in the event that the plug is shifted in any manner, an aggregate reading is taken once again. The four jets each detect four changes in pressure and sum them up. The total—and the readout on the indicator—changes whenever any of the recorded dimensions fluctuates.

On the plug, the 4 jets are usually at equivalent levels or planes. The 4 jets may theoretically be moved individually anyplace along the plug, and in the event that they are situated at ninety degrees relative to each other, they would measure the bore’s mean diameter. The 2 jets on top are counterbalanced by the 2 jets on the bottom, resulting in no change in the show. The aggregate pressure fluctuates if the bore is not completely straight, and the differential would be displayed on the instrument.

Dynamic Measuring

The display gives a number in the event that the straightness plug is merely put into the bore. The key question is what that figure implies. Whenever the jets are aligned with the bow, according to the orientation, they obtain their maximum or minimum reading. When the plug is rotated one hundred and eighty degrees, the outer and inner jets switch roles and show the same value, indicating that the plug is in a differential state.

However, when the plug rotates one hundred and eighty degrees to explore the bore, the sets of jets would have a peak clearance, followed by a minimum clearance, generally at ninety-degree angles to one another. As viewed along the whole extent of the plug measuring length, the difference between the greatest and minimum value would be the out-of-straightness state.

In manufacturing, the design of each component contributes to and determines the usefulness and effectiveness of the end product. If concentricity is not measured and remedied before the product is sent into manufacturing, it could create a chain reaction that will cause serious issues later down in the assembly pipeline. This is highly cost-ineffective as it would incur high costs for your project. Therefore, concentricity must be measured and ensured of the right value. In addition, all the parts should work cohesively together before the product design is sent into production.

What Is Concentricity?

Concentricity is considered a type of complex tolerance, and its value is calculated to determine to which extent the geometric shape would be closest to the ideal form. First, median points of the spherical and cylindrical parts are established. Then, when the piece is concentric, the thickness of the internal and external walls will be consistent and equidistant. This would be critical in ensuring that the dimensions of the finished products will not exceed the manufacturing tolerances, which helps in fitting parts accurately in their intended application and will prevent any unintended vibratory movement and resistance.

What To Choose: Concentricity or Total Runout?

Concentricity is measured or calculated using a process also known as total runout. The two types of measurements are similar, but they vary in specific components. Both are determined using an axial orientation or alignment and also pose the challenge of being difficult to calculate. The median points are established in a spherical and circular axis in calculating concentricity. At the same time, the total runout is determined by fixating a datum point and then turning the part around to ensure median points fit within the tolerance zone.  

How Is Concentricity Usually Measured?

There are three ways concentricity is usually measured to ensure minimal error in the manufacturing process. The first is using a sample drawing to map out the axes of the cylindrical or spherical shape, and the aim is to ensure the median points are accurate coaxially. The next most commonly used method is using an equipment called the dial gage.

The dial gauge is placed on the circumference’s vertex of the product, where the axis of the tolerance would be determined. Then, the product would be rotated, the maximum and minimum runout values would be calculated, and the specified circumference would be measured. This difference in maximum and minimum values would be considered concentricity.

The last way concentricity is measured would be through a coordinate measuring machine, where the circle of the plane is calculated instead of coaxially. Then, the stylus is placed at the datum circle’s measurement point and the target circle’s measurement point, where the concentricity is measured.

Why Choose Willrich Precision?

Willrich Precision offers over four decades of inspection, metrology, and gauging experience. We  provide a vast range of services and products to clients, including advanced metrology technology and measurement equipment for vision and laser systems. Furthermore, we take great satisfaction in establishing ourselves as a pioneer in measuring instrumentation technology and, as a result, can serve a diverse spectrum of clients from various sectors. Every client connection is given top priority. That is why we offer you a free consultation and access to our team of seasoned professionals that are highly competent and can assist you.

Please contact us at info@willrich.com now for more information about our inspection and metrology services and products!

Concentricity limits how asymmetric the shaft will be in relation the datum axis. If the shaft is oval without being a perfect circle, it can still considered concentric. By imposing diametrical symmetry, it regulates mass balance about the datum axis. It does not influence the size or taper of the shaft. At the same axial location along the datum axis, it compares the radius on one side of the shaft to the radius on the other side of it.

Runout limits how the unbalanced circular or spherical shaft relates to each datum point located along the shaft. In the scenario where the shaft may be perfectly circular or round, if its axis deviates from the datum point, it will be considered a runout. However, the shaft size is not caused by the runout and runout has no control over the other forms, but only affects the variance of the radius-to-datum in each location.

How Similar Are the Results?

Position specifies the volume in which the shaft’s surface must remain. The shaft surface’s volume must remain in is determined by the shaft’s maximum permissible diameter alongside the tolerance of the position. The volume the axis must retain the tolerance of position and the maximum material tolerance allowed. The surface approach is the one to use. Any approach should produce relatively comparable results for an actual component, and they are also mathematically equivalent.

What Is the Difference between Runout and Concentricity?

Concentricity is the circular form of geometric dimensions and tolerance symmetry, while the runout combines both circularity and concentricity. The runout will equate to concentricity if the component is perfectly spherical and round. However, what is circularity in this text? Circularity would determine the form, orientation, and location and usually cannot be referenced to the datum axis. However, the only exception would be when the size tolerance is tighter than the runout tolerance.

Concentricity considers how a cylindrical shape is positioned on a theoretical axis. In contrast, the runout considers how the target deviates from the dimensions of a circle when it is perfectly positioned on the rotation axis. However, when the part is measured using a similar cross-sectional plane, this is considered a case of coaxiality, as the internal diameter and outer diameters of the shaft or tube are compared.

Why You Should Choose Willrich Precision

Willrich Precision has over four decades of experience in inspection, metrology, and gauging. Clients may choose from a wide range of services and products, including modern metrology technology and measuring equipment for vision and laser systems. Furthermore, we take great pride in establishing ourselves as a leader in measuring instrumentation technology, allowing us to service a wide range of clients from numerous industries. Every client connection is treated as our first priority. That is why we provide you with a free consultation and access to our team of highly qualified individuals that can assist you.

For more information about our inspection and metrology services and products, don’t hesitate to contact us at info@willrich.com today!

Concentricity is a value used to calculate the extent to which a geometric shape in CNC (Computer Numerical Control) matching is closest to its ideal form. This measurement is commonly taken in CNC machining to ensure high precision and quality during the production stage to ensure manufactured parts fit perfectly together and minimize errors. There is value to measuring the concentricity of a product during CNC machining, including a greater assurance that the dimensions of prototypes will not exceed their manufacturing tolerances. In this article, we dive deeper into the meaning of concentricity and how it is used in metrology to expedite the product development pipeline.

Why Do We Need to Measure Concentricity?

The bottom line in the pursuit of product development is to ensure that workpieces do not vary too from having perfect symmetry, especially when a machine processes it. In many cases, deviation from having the ideal symmetrical balance can be costly, resulting in material waste and higher production costs. Most importantly, it will create flaws and issues later in the production process. Therefore, it is usually measured in an axial or radial orientation to examine the extent of the error in the different dimensions. However, as this process is considered complex and difficult to implement, it is only used in specific situations and when needed.

How to Measure Concentricity?

The value of concentricity is usually calculated using the two diameters of the hole – one for the hole and the other for the shaft. They signify the outer boundary and the inner line, respectively, and both are necessary to examine the deviation in surface measurements. Additionally, depending on the company’s protocols, they can be measured in imperial units (inches) or metric measuring (millimeters). As mentioned before, measurements in CNC machining are made in the axial or radial orientation; therefore, three methods are considered relevant in this aspect.

1. Radial Error – The measurement variation between the feature’s center on one side and the corresponding point on the other.
2. Axial Error – This is calculated by subtracting the distance from machine zero to a datum line and then calculating the deviation from this line at two locations along its length.
3. Overall Accuracy – This value is obtained by adding radial and axial errors together, or it can be pre-calculated (empirically) because certain machines provide complete concentricity

A Common Challenge in Concentricity Measurement

The dial indicator is one of the most common ways in which engineers measure concentricity and it is usually done in both directions. It will measure at a 90-degree angle to the longitudinal axis and at a one-sided offset. However, it poses the challenge of requiring sufficient space of up to 18 inches to inset the spindle tip of the equipment. Additionally, you will need to be extremely cautious of any accidental breakage or deflection of the rotating components during the measurement process.

What We Offer

Here at Willrich Precision, we have almost half a century of experience in the metrology, gaging, and inspection fields. We offer a great variety of products such as basic measuring tools, metrological technology, and equipment like vision systems, laser systems, and micrometers. We are a pioneer in measurement instrumentation, and we are dedicated to helping you make informed and intelligent decisions for your business operations like CNC machining.

For more information about the product and services Willrich Precision Instrument offers, please do not hesitate to contact us today!

Metrology is the scientific study of measurement and it ensures that the calibrated CMMs deliver precise and accurate results with provable validity. The purpose of metrology is to maintain measurement standards while developing new methods of measurement and ensuring that these methods are standardized and accepted around the world.

CMM calibration artifacts are important tools in metrology and have consistently been used to check for the quality of CMMs. Here are some reasons why they have been hugely important.

Ensures Accuracy

CMM calibration artifacts play an important role in metrology as they ascertain the measuring accuracy of the CMM. This ensures the performance and quality of the CMM and its ability to deliver precise and reliable measuring results.

This is done through the measurement process which assigns values to the property of an artifact and uses that as a benchmark for comparison against the measurement values of the CMM. The CMM calibration artifact thus helps to reduce or eliminate any bias and discrepancies in the measurement system of the CMM relative to the benchmark.

Verified and Traceable

Calibration artifacts, as the name suggests, have been calibrated. They are also traceable and all their measurements have been previously verified in the laboratory via a documented process, resulting in the calibrator’s drift errors being eliminated.

This makes them an excellent tool to calibrate CMMs and for their values to be used as a reference base to that of the CMM’s measurement values. This further eliminates any uncertainties or doubts about the precision of the measurements of the artifact.

Ensures Longer Life Span of CMM

CMM calibration artifacts also help to ensure a long instrument life span of the CMM. The CMM will wear down over time and much faster if used frequently. Rather than throwing away the CMM and replacing it every time it stops providing accurate measurements, you can use the calibration artifact to calibrate its measurements back to the correct levels. This is critical to the metrology and measurement precision of the CMM.

It also extends the life span of your CMM and prevents unnecessary expenditures while cutting costs. Moreover, the calibration artifact can also help you monitor the rate of degradation of the CMM and track other factors such as frequency of usage or environmental pressures that lead to faster wear and tear of the CMM.

Using this information, you can make the necessary adjustments to mitigate these factors and prevent extended wear and tear of the CMM. This ensures that your CMM is kept in a better condition for longer.

Increased Safety

Metrology ensures predictable performance from your measurement tools such as the CMM. Another way calibration artifacts are hugely important to metrology is because they help to increase the safety of CMMs through calibration, by ensuring the CMMs measurements are consistent and precise.

Minor inaccuracies may result in the CMM working incorrectly or false information about the safety of a certain product. Through regular calibration of the CMM via a calibration artifact, the CMM’s measurements will be more reliable and accurate, while also reducing unsafe situations.

A coordinate measuring machine (CMM) calibration artifact is used to ensure that the measurement data created by the CMM is accurate through regular calibration. The CMM calibration artifact also includes an ISO-17025 accredited certification and most CMM calibration can be accomplished through the use of a calibration artifact.

Importance of CMM Calibration Artifact

The CMM calibration artifact is an important tool that helps to gauge any inconsistencies or errors in the CMM measurements. This helps in providing accurate calibration data and in fixing or integrating any inconsistencies into the data. A CMM machine can have errors along 21 different measurement axes, thus depending on the severity of the errors, calibration may or may not be required more often.

Artifact Usage

The calibration artifact may be attached differently to the CMM depending on the type of calibration being done and the type of probe used. Some artifacts require a mounting bracket to be held in place for the calibration process while others can be mounted directly onto the CMM.

The calibration process involves measuring the artifact along with a fixed measurement plan and comparing the data points against the known dimensions of the artifact to check for consistency. By doing so, any error that prevents the CMM from accurately performing its function and measuring the inspected parts would be removed.

Different Artifact Types

Calibration artifacts help to measure the accuracy of measuring machines and this is done through the artifact containing a variety of geometry types such as spheres, cones, circles, and many more. Some common calibration artifacts include the ball plate, KOBA step gauge, end bar, hole plate, and swift-check gauge. Different artifacts may be chosen for the calibration of the CMM depending on the type of measurements being performed and the probe used.

Reminders when Using Calibration Artifact

When choosing a calibration artifact, it is best to choose an artifact that is similar in hardness to the material that is being measured. This is to prevent any inconsistencies due to material or probe deformation. Moreover, once the calibration artifact is installed in the CMM, it has to be given time to cool down and disperse its heat as the artifact is temperature sensitive and will react to the body heat transferred from the technician’s hands.

Sometimes when the CMM involves very precise measurements, the environment can also affect the calibration process. For example, differences in temperature or air currents in the lab can affect the calibration process. It is thus best to strictly control conditions when attempting to calibrate the CMM using an artifact to minimize any discrepancy.

Artifact Form and Material

The calibration artifact may differ in form and material depending on the kind of probe you are calibrating. The stiffness of the artifact material is also an important consideration when deciding which artifact to use as the contact force of the measuring probe may dent or deform the artifact. CMM calibration artifact forms also do not follow any specific rules due to the broad range of uses for CMMs.

Concentricity gages are utilized for inspecting the rotating parts’ exterior, internal, and flat surfaces. They also enable the co-axiality of more than two diameters to be measured and allow you to determine the runout of axial measurements. In short, they are designed to resolve inaccuracies in product dimensions and expedite manufacturing processes by providing accurate and reliable measurements. In the market, there are a wide variety of gages that are customized to meet unique and specific

Smart Spin Gage

The Smart Spin Gage is designed to measure the cylindrical components of the outer diameter and part edge runout in a short time (perpendicular to body diameter). The equipment incorporates a backstop that can be adjusted, roll clamping, and probe placement that can be orientated vertically and horizontally to handle a variety of component designs, geometric shapes, and sizes.

This product’s precision rotation and remote indicator RESET are enabled via an integrated STEPPER motor with specific drive control hardware and software. These specifications and features provide consistent outcomes with the correct setup for various component shapes and sizes within a given part size range. Additionally, component testing is available at two speeds – 10 and 20.

Universal Punch Concentricity Gage – Model A-10

The Universal Punch Concentricity Gage is a series of basic gage and standard carriers, comprising three major components – the gage model, main rollers, indicator, and accessories with this model. The concentricity gauges are classified into two types immediately, which are traceable to NIST. In this case, the accuracy of the standard black gage is assured to be =4um, while the precision of the gold gage is guaranteed to be =8um.

St. Mary Rotary “V” Block Gage

The accuracy of St. Mary Rotary “V” Block Gage speeds up the determining process of concentricity features, especially on cold-headed items. In addition, as compared to other comparable devices, it is much more simple and accurate. Geometric tolerances are necessary and required for cold-formed fasteners. This St Mary Rotary “V” Block Gage will be able to meet this need, being able to accommodate tight diameters.

Universal Punch Concentricity Gage Model H

Similar to Model A-10, the Universal Punch Concentricity Gage Model H consists of three main components – the gage model, main rollers, indicator, and other accessories. The part diameter and length capacity can be customized up to 1″ and 12″, respectively, while the gage length, width, and height are 12.5″, 5.5″, and 9″ approximately.

Work with Willrich Precision

With over four decades of experience inspecting, gaging, and metrology, Willrich Precision can confidently and effectively offer our customers a wide variety of products and services. We are equipped with the right equipment to support complex metrology measurements with sophisticated technology and measuring tools in laser and vision systems.

Taking pride in our role as a leader and supplier for measurement instrumentation technology, we have served a wide base of different clients from various industries. Our relationship with every client is unique, special, and valued – that’s why we offer a free consultation to allow you to speak to our team of expert, high-qualified service professionals who can provide you the help and assistance you need.

For more information about our range of services and products, please contact us at info@willrich.com today!

In the field of Geometric dimensioning and tolerancing (GD & T), concentricity is one type of complicated tolerance. It is usually used to establish the tolerance boundaries (otherwise called tolerance zone) where the median points of a spherical or cylindrical product design or feature are. It is often used for high precision components and when median points will need to be controlled. However, since measuring and verifying concentricity tolerance is a complex and time-consuming process, many engineers and product designers prefer and are usually advised to employ runout or position tolerance.

What Is the Tolerance Zone?

Establishing the tolerance zone before the manufacturing process is critical as this will determine the cost incurred and the success of your project. It is defined as the pre-determined horizontal length that extends from the outer edge wall to the opposite side. Concentricity establishes a 3-D cylindrical or spherical tolerance zone surrounding the datum axis, and all the central points will lie within the boundary. The diameter of this zone is considered the permissible and appropriate value for this callout.

When is Concentricity Tolerance Used?

Concentricity tolerance is complex and complicated; therefore, it is difficult to measure and calculate. It is usually used in transmission shafts, gear, or balancing equipment. This concentricity tolerance will determine the dimensions and size of the driving shaft to prevent any wobbling. First, the part’s real median axis must be determined to ensure concentricity by computing the midpoints of diametrically opposite locations. The median axis is obtained by connecting all such median sites. For the part to be approved in a standard engineering and designing process, all points on the median axis must be inside the cylindrical tolerance zone.

How is Concentricity Tolerance Measured?

The concentricity tolerance can be evaluated or measured in four basic steps. First, you will have to establish and identify where would the point of the datum plane, surface, or axis lies. Next, you will plot the points on the outer profile’s controlled surface, which can be determined using the CMM or a coordinate measuring machine. Then, you will have to measure and calculate where the central points and axis of the plotted profile are at different cross-sections. Lastly, you will need to verify where the positions of the central points within the cylindrical tolerance zone are.

Choose Willrich Precision

Willrich Precision has a well-established history of more than four decades in the fields of inspection, gauging, and metrology and carries a wide range of measuring tools, metrology equipment, and high precision instruments. We are considered by our clients as a pioneer in measurement instrumentation and are privileged to be able to serve a diverse range of clientele.

In our role as a frontrunner and provider of measurement instrumentation technology, we have served a wide range of clients from many industries. Our relationship with each client is exceptional, superior, and treasured – get in touch for a free consultation and speak to our team of highly-qualified service professionals who can provide you with the assistance you require.

For more information about our products and services, please feel free to contact us today!

Calibration artifacts are critical to the performance and quality of your CMM. They also help to ensure your measurement data are precise, accurate, and reliable. However, there are numerous calibration artifacts to calibrate different measurements.

Likewise, there are different types of CMMs and they can have errors anywhere along the 21 different measurement axes. Using the proper calibration artifact allows you to fix the corresponding measurement error and address any anomalies or discrepancies in the measurement data. Here are some tips to choose the best CMM calibration artifact.

Level of Precision

Before attempting to calibrate the CMM, you should first assess the level of precision required for the calibration. Is it simply to calibrate the faulty height measurements of the CMM? Is it to calibrate the probe angle of the CMM? Understanding the level of precision will give you a better analysis as to which calibration artifact to use.

This is because some calibration artifacts are better suited for high-level precision calibration while others are used for simple and daily calibration. For example, the swift check calibration artifact performs simple and quick checks on the CMM and delivers easy and clear results.

It consists of a length bar, ring gauge, and sphere that comprises all the geometries and directions required to check for the performance of the CMM. It helps to check for the daily measuring accuracy of every part of the CMM and has a standard precision level for calibration.

However, in cases where a higher level of precision is required in the calibration process, a laser interferometer is used. The laser interferometer is a calibration artifact that utilizes a laser with a beam splitter to make extremely precise measurements based on the reflected laser light.

Calibration Process

There are numerous CMM calibration processes and they require different calibration methods and artifacts depending on what you wish to measure. All calibration processes measure an artifact against a fixed measurement plan and the data points act as a reference base to be compared against the known dimensions of the artifact.

From there, the faulty measurements are rectified and the CMM is calibrated to remove any errors that would prevent it from accurate measurement. For example, if you wish to perform a coordinate calibration process or calibrate the height measurement of the CMM, you may choose a KOBA step gauge calibration artifact.

To perform a dimensional measurement calibration process, a rectangular gauge block would be used due to the vast selection of gauge blocks available.

Probe Material

The probe material is another important consideration in choosing the best CMM calibration artifact. When performing a CMM calibration, you want the artifact to be pretty similar in hardness to the material being measured.

This is because there will be contact force from the measuring probe to the artifact, thus if they are both similar in hardness, it will prevent any inconsistency or error in calibration results due to material or probe damage. Significant errors occur when the hardness of the material varies widely and this will affect the measuring accuracy of the CMM and the calibration process.

CMM calibration artifacts are important in ensuring the precision of CMMs and that they are working well within their specifications. This ensures the safety, quality, and innovation of CMMs and improves overall production and services.

If you look around your room or house, most of the items were produced within tight measurement specifications assured by calibration. CMMs are commonly used in various industries and through proper calibration using an artifact, their measurements will be more reliable and consistent. There are various benefits to using calibration artifacts and below are some of them.

Data Collection

Using a calibration artifact allows for data collection, generation, and analysis. To do so, the calibration artifact has to include sophisticated analog hardware, along with a microprocessor and software. This provides the calibration artifact with the internal comparison capability and references available to collect and track data at the time of calibration.

Measurement and tracking of any performance changes and drift relative to the internal references can likewise be stored for further analysis. This could come in very useful when a CMM that is reviewed once or twice every year goes out of calibration without the knowledge of the user. If critical tests and results rely on the CMM, this may have dangerous and costly consequences.

However, by using a calibration artifact with the necessary technology for data collection, external calibrations can be done alongside internal calibrations. Internal calibrations prevent the CMM from going out of calibration through the monitoring of the CMM performance between calibrations. This minimizes the chances of the CMM having to be constantly calibrated at the lab.

Data Analysis

Data from the calibration artifact can be stored and analyzed using statistical algorithms such as standard deviations. Artificial intelligence can also be used to analyze the given data to make better recommendations or simply list the important findings. Analysis of data is important as it allows the lab personnel to accurately pinpoint the cause of measurement errors in CMMs and how frequently they occur. This allows the user to better predict the performance of the CMM and take any necessary actions accordingly.

Versatile

Numerous calibration artifacts can be used for a variety of CMMs and different measurement axes. Different artifacts can also be used when there are different hardness or stiffness of the material to be measured in the CMM. For example, a swift-check gauge is a calibration artifact that comes equipped with a length bar, sphere, and calibrated ring gauge that incorporates all of the geometries and directions needed to check the performance of the CMM. It is versatile and can be used for small to medium-sized CMMs.

Confidence in Performance

Calibration artifacts give users confidence in the reliability and precision of their CMMs through checks and delivering results that are clear and easy. It further eliminates the cost and implications of a CMM being out of specification during use. Calibration artifacts ensure that CMMs provide better performance while fixing and minimizing any errors.

A CMM calibration artifact helps to ensure the precision and accuracy of the measurement data from a CMM. This assures reliable results and benchmarks such as safety, quality, and equipment lifespan.

All CMM calibration artifacts adhere to the ISO 10360 series when performing calibration. Using calibration artifacts allows users to independently check and ascertain the measuring accuracy of the CMM as well as to detect any inconsistencies and correct them accordingly. It thus minimizes uncertainties and errors to an acceptable level.

How to Determine Calibration

A CMM can have errors along 21 different measurement axes. This means that a wide variety of calibration artifacts can be used to correct these errors and to ensure the accuracy of calibration data, which contributes to the fixing of these errors and their integration into the data system.

CMMs have different levels of calibrations which could range from weekly checks to checks once or twice every year. To effectively determine calibration, the error and inconsistencies in measurement data first have to be sieved out to determine which measurement axes are faulty. The corresponding calibration artifact can then be used to calibrate the measurement for that particular measurement axes.

Artifact Types

There are different types of CMM calibration artifacts used during the calibration process. This is due to the different measurements that can be calibrated in a CMM. Some common artifact types include the swift-check gauge, ball plate, ball and cone, end bar, length gauge blocks, and the KOBA step gauge. When choosing an artifact, it is important to choose one that has a similar hardness to the artifact being measured to prevent any probe and material damage.

Certain artifact types will be better suited for certain CMM calibration. Most CMMs require a custom artifact. For example, the KOBA step gauge consists of a one-dimensional test body with planned parallel measuring surfaces. It is best used with small volume CMMs such as multisensory systems and monitors height gauges.

Calibration Process

There are different calibration processes involved which require different methods and calibration artifacts depending on what you wish to measure. The calibration process involves measuring the artifact along with a fixed measurement plan.

This allows for a comparison of the data points against the known dimensions of the artifact and easier cross-checking in the event of any anomalies or inconsistencies in the data set. The result would be a calibration of the CMM that would remove all errors and allow the CMM to perform its function of accurate measurement.

Laser Interferometer

A laser interferometer is only used when a high level of calibration is required. It is also a calibration artifact and utilizes a laser with a beam splitter to make extremely precise measurements using the reflected laser light.

The interference pattern created by the reflected laser light is tracked and so are the CMM’s movements via computer software. Any anomalies or inconsistencies in the data set are likewise corrected. The laser interferometer requires a longer calibration time than other artifacts and should only be handled by an experienced technician.