Indicating Plug Gage

Image Source: Diatest

Consider the Indicating Plug Gage

It uses the plug body, not the contacts, to center the age.

March 25, 2024

Checking bores with submicron resolution is difficult to do with most handheld gages as human feel impacts the readings. If you want to check those bores while the workpiece is still in the machine the level of difficulty only rises. Today’s applications call for a more accurate solution that is not influenced by the operator taking the reading, one that allows you to sweep the bore looking for signs of taper and ovality as well as size and then record those readings seamlessly.

Since not every application allows a gage to be tethered to a work bench, the Indicating Plug Gage which uses the plug body, not the contacts, to center the gage is another option to consider. It uses an internal probe and needle design that have been perfected over the last 50 years. This style provides two benefits, first the readings are more stable than sweep or triggered gages as the gap between the plug and the part is typically around .001” and the contacts are always in position taking a reading because the body is performing the task of centering the plug.

This means operator influence is all but eliminated—everyone who uses the gage gets the same results. Another plus is accuracy, if you need the higher resolutions there are products out there with up to .000005” resolution that give you repeatability of .000020”.  The combination of newer electronics and better production capabilities has removed the limits on what can be done without being tied to cords, benches or air lines as wireless features allow all sorts of readings to be recorded and stored with ease.

Some of the other benefits are the plugs contacts, with choices like carbide, DLC, ceramic, chrome and more they can find the right contact based on the material you are checking. Larger radius contacts can help smooth out rough finishes for more stable readings and since the contacts are always engaged picking up a reading of a short bore, or a blind bore, is not difficult at all. Even adding contacts to measure multiple spots on a bore or a multiplane plug that checks a combination of bore sizes with a single plug is possible.

All these readings can then be stored in a variety of data collection devices, and in most cases that includes ones you already have in-house since the readouts need only be available with a 3/8” or 8mm stem especially if you only need .000050” resolution. For specific applications you need only share a print with the design engineers and they will let you know what is possible. Don’t think you cannot achieve the high resolution readings your parts demand, the solutions are out there being used on shop floors, labs and even in the machines making the parts.