Checking Mic's

One common use of gage blocks in the shop on the machinist side of things is to periodically check your instruments. If your micrometer is off, your work will be off. Therefor if your tooling as a whole is off your ability to measure your parts will be. No matter how well you can make your parts read right according to your tools by using your machine properly, if your tool is off the work is off.

Although in many shops there will be a quality control or quality assurance office (referred to as QC for the remainder of this website) that deals with the inspection of product the shop produces and the measuring tools that the machinists use, its always good practice to check your own tools periodically between inspection cycles. Remember a poor machinist blames his micrometer when he can check the micrometer himself simply by using a couple of gage blocks.

First I will show you how to check a outside micrometer, specifically a 0-1" micrometer. As you will see, the micrometer actually has a QC sticker attached from the company I was working at. However periodic checking of ones tools is of prime importance due to the possibly long cycles of inspection of instruments allowed in ISO 9001 standards and other internationally recognized standards in use in various shops.

When first checking your micrometer, its always best to check your micrometer that it will indeed zero out properly.

Now that we have done that, we can proceed and check it at the 1.000 mark (all the way open position) using a gage block to see if it will properly read at that distance.

Now that we have that checked you should check that the middle area of the spindle is actually measuring right, due to the effects of combined errors over the spindle you may read the previous 2 situations properly but the spindle may be off in the middle.

Now that the middle is checked, I generally use a .113 block to check the micrometer at a half spindle revolution. This should also be done just using the .113 block at the opening of the micrometer, however I will now show that on the website.

Now that the micrometer has read correctly we know that when we take our measurements it will
measure correctly. One thing to remember however with ratchet type micrometers is that you must always "click" the ratchet the same number of times to consistently apply the same measuring force.

As you can see personally I use and prefer friction micrometers that use a more tactile feeling of the pressure to measure, which is more of a user dependent method. However either method works, and getting accustomed to both is a good idea.

Dimitrios Simitas