How To Measure Small Bores

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.

by George Chitos

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