Much has been said and written about statistical process control, commonly referred to as SPC. Shop owners seem to keep off the process, citing reasons such as how expensive SPC gaging equipment are or how small their facilities are. These two reasons can best be termed as misconceptions. SPC is not as complicated as most people think. Secondly, you do not need complex computerized systems and costly software to get into SPC. You should therefore benefit from gaging for SPC, as much as your competitors do. But before that, here is how to simplify the whole gaging process.
You do not need to be a statistical genius to understand what gaging is all about. However, you need to have a basic understanding of how the process works. This should not be difficult, especially because SPC and gaging principles were first developed in the 1930s, decades before the computer was invented. Much hasn’t changed since then as far as gaging is concerned. With that in mind, gaging terminologies should not intimidate you. You only need a basic understanding of data collection and charting. This should not be a problem as there are several free guides both online and offline that can come in handy for a newbie. In a nutshell, the process is all about collecting measurements, averaging the measurements and then accurately charting the results.
The Actual Task
This involves three main steps. The first step involves identifying the part you wish to measure. You should then identify vital dimensions and what part of the process controls the dimensions. This is what you wish to measure and where you would like to start the process. Remember to keep everything simple. To achieve that, start with a single measurement until you figure out how the process works.
Use the best gaging equipment you can get. Then follow all the aforementioned gaging basics to avoid errors. To make things easy, use the ten to one resolution rule. That is, use a gage with at least 0.0001 resolution to measure a 0.001 tolerance. Be sure to run a series of gage repeat and reliability tests, which are also commonly referred to as GR & R. This will go a long way to make sure your measurements are accurate. Always remember that your analysis can only be as precise and accurate as the measurements you choose to start with.
The Machining Process
Find out if your machine can hold tolerances and control the limits you need. Only then, will you be ready to gather data. Again, this should be very easy with automated gaging devices that make data collection and measuring easy. In a nutshell, stick to charting electronically. This will put you in contact with the process. You will then be able to see the link between what you’re doing and what the charts show. Simply put, you will be control of the whole process. Remember that the other advantage of collecting data and subsequently using the results is that you can use any type of indicating gage, as long as the gage is accurate.