Outside Micrometer Calibration - How to Calibrate - Mitutoyo

Hello, I’m Jim Salsbury with Mitutoyo America Corporation and welcome to the metrology training lab in this episode we're going to talk about the calibration of an outside micrometer in past episodes we've defined the concept of calibration discuss the purpose of calibration and introduced important aspects of what makes a good calibration method in this episode we'll apply all of those ideas to the calibration of an outside micrometer calibration is a search for airs and we want to develop a calibration method that efficiently hunts down and finds any potential errors in the measuring instruments so how do we do that best for a micrometer? well there's a nice American standard called ASME B89.1.13, and the calibration method that we'll be discussing is based on that standard calibration usually starts with checking out the proper operation of the micrometer is there any obvious damage to it does it move smoothly across its measuring range do you feel any play in it do the buttons work correctly does the clamp work once you are satisfied with the operation then we begin the accuracy tests here at minatoya we recommend using a micrometer stands micrometer is a precision measuring instruments and the stand helps eliminate the transfer of your body heat to the tool the stand also makes the measurement a bit easier which may help improve your accuracy the first step is to clean the measuring faces we'll put a little bit of solvent on a cloth and we'll pinch the cloth between the measuring faces like this right then we'll bring the measuring faces together to set our zero for all of our measurements will want to properly use the micrometer this one includes a ratchet mechanism to control the force we want to apply a nice smooth consistent force and listen for several clicks of the ratchets the zero is so important we'll want to check that a few times the most important skill and calibrating micrometer x' is simply using a micrometer correctly if you are having some struggles getting good results find yourself a mic that is known to be good grab some gauge blocks and practice it doesn't take too long to get the right feel once we have our zero sets we'll check the micrometer at the first test points we recommend the use of gauge blocks there really isn't anything better to use and you need something pretty accurate so gauge blocks make a good reference standard for calibrating micrometers the ASME standard recommends five specific size gauge blocks for calibration in inches these sizes are the 210 block for twenty six oh five eight 15 and one inch the reason for these specific sizes is that they will force the micrometer thimble to be in different orientations for each test points remember that the goal of a good calibration method is to have an efficient test and the use of these five test points will look for airs across the measuring range simultaneously with the rotation of the thimble these five blocks are the most efficient tests but if you don't have these special sizes you can choose to use others that achieve the same goal the principle is what is important not these specific sizes if you do use different sizes such as from a standard set of gauge blocks you will likely find yourself needing a few extra test points you can use any style or material gauge blocks for this calibration I'm using rectangular ceramic blocks we like ceramic blocks for calibrating mics due to their thermal properties ceramic blocks thermally expand about the same as steel but they have a much lower thermal conductivity which means your body heat won't affect them as much as steel blocks and since you have to handle the blocks during calibration this is a useful advantage we also recommend the use of grade zero gauge blocks grade zero blocks are sufficiently accurate for micrometer calibration so you can just use the value that's on the block which makes the calibration more efficient so let's clean our gaze blocks and take our first test point using a two ten block glaze box should be properly calibrate across the measuring faces so it doesn't matter where you measure on the blocks some people like to measure near the ends others in the middle it shouldn't matter again we want to use them a crumber properly and control the forest as best as possible make sure the measuring faces are contacting the grades blocks without trapping any air or dust between them a proper measurement should not be too tight or too loose but the gauge block should feel like it is in full content it should allow for some slight smooth movements like this it's common to take a few readings with the goal to ensure that you have a consistent value this is typical practice when using a micrometer it is not correct however to take a bunch of readings and report the average during the calibration micrometer should repeat within the specification limits for the length accuracy and if not then you should reject the micrometer the reported error is the measured value minus the value of the gauge block to be more efficient it is often useful to not record the entire measured value but just the observed air this digital micrometer in inches as a 50 millionth resolution and so the readings will be something like zero plus 50 as in this case or minus 50 millions in metric the errors will be something like zero one or minus one microns now if you don't understand millions for microns go watch the episode of the metrology training lab that covers units of measure I'm using this datasheet that we use in some of our calibration classes and it's just for training purposes you can use any sort of form that you are I'll write down the entire value in inches and the air and millions for this digital micrometer the tolerance is plus or minus 50 millions or plus or minus one micron in metric which is typical for a digital micrometer I'll now continue along with the other readings until I complete all four positions the length tests are now complete but that is not the only important test for micrometers the flatness and parallelism of the measuring faces also needs to be checked historically the flatness and parallelism was checked using an optical parallel like this now this method is a bit cumbersome and requires some special skills in reading optical fringe patterns so instead of checking the micrometer in this manner the ASME be 89 113 standard presents a much simpler method the reference standard that we'll use instead of the optical flat in parallel is a small sphere like this ball gauge here you can also use a stylus from a coordinate measuring machine if you'd like so we're going to start by measuring in the middle of the measuring faces and then set our zero there all right now we're going to move the ball across the measuring faces up and down backwards forwards across the measuring faces any variation in the size is due to the flatness or parallelism of those two measuring faces then we'll report the range of those results the maximum minus the minimum is reported as what we'll call the parallelism in this case I saw no range and so the reading would be zero now this method is generally not as accurate as using the optical parallel but it's easy and efficient to do when a calibration method is not easy to do and it is not the primary test we often see labs skip units so we recommend using the ball because anybody can do it it's a much better than not doing anything at all we've also heard that some labs will use the optical parallel or optical flats if the test with the ball fails because you can get a better idea of why it's failing that seems like a pretty good idea but we'll save using the optical parallel or flat for future episodes of the metrology training lab so that completes this micrometer calibration it looks like this micrometer is in tolerance so that was the calibration of a 0 to 1 inch micrometer now in a 0 to 1 inch micrometer we can bring the measuring faces together to set the zero what about calibrating larger micrometers a one to two inch micrometer 2 or 3 inch micrometer or up nineteen to twenty inch micrometer well they're calibrated in a similar manner but you need to use a reference standard so let's cover that larger micrometers generally come with micrometer standards such as this these standards are useful for the shop floor setting of the zero by the user but they are not recommended for the calibration of the micrometer instead you should use a gauge block in this case this one inch gauge block I'll use for this one to two inch micrometer now I'll set my zero using this gauge block and then I'll proceed using the same five gauge blocks that I used before for the one to two inch mic this time however I have the added complication of needing to ring each of these five blocks to the one inch block it's very important to ring each of these blocks one at a time to the one inch reference thereby eliminating any air in this one inch block from affecting the readings this is particularly important as the micrometers get much larger let me wring these blocks together and then we'll take a reading to demonstrate the method you would then continue with the other four blocks to complete the test for the parallelism of a larger micrometer the benign one thirteen standard recommends a test similar to the small ball but instead uses the edge of a gauge block my zero is already set with this gauge block now what I'm going to do is move the gaze block up down in and out to look for variation and I'm going to measure right at the edges like that and like that and then down and then up this time I see a minus fifty millions reading so the range of all my numbers would be fifty millions and that would be in tolerance and that's the calibration of outside micrometers remember the method we just discussed comes from the American national standard on micrometers asme dat nine point one point thirteen if you don't like the method you're always welcome to come attend the next ASME B89 standards meeting to discuss it further thank you I'm Jim Salsbury and we'll see you next time from the metrology training lab

Channel: Mitutoyo America Corporation

Views: 58,309

Rating: 4.7990432 out of 5

Keywords: outside micrometer calibration, outside micrometer calibration procedure, micrometer calibration, outside micrometer, micrometer calibration procedure, calibrate outside micrometer, calibration, calibration lab, calibration of measuring instruments, calibration training, calibrate micrometer, digital micrometer, metrology calibration, mitutoyo micrometer, metrology, metrology lab, metrology training, Metrology Training Lab, Mitutoyo, how to calibrate, gauge blocks

Id: NrLLmwi7-vE

Length: 16min 11sec (971 seconds)

Published: Mon Jul 23 2018