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[Metrology] How to develop a feel for measuring round rods with a micrometer?
- Thread starter WobblyHand
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I like to work hold a .00005 tolerance.........
No one said it yet but make sure to calibrate your mics with a gauge block or the standard that usually comes with a new mic..... If you skip this step then all your measurements will be wrong and it will seem impossible to get it to match your digital calipers.....
Nah, matching the digital calipers is easy peasy. Remember the mic reading and then adjust the squeeze on the caliper until the readings match.
With digital calipers I can get any number within a 0.005 inch range with casual technique.
With digital calipers I can get any number within a 0.005 inch range with casual technique.
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Try not to use it like a c-clamp.....lol
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Not truly crummy, I suppose, but not top tier by any means. The 1-2" mic is part of a 0-4" set I bought from Shars. It's all mechanical, no digits, just read off the lines. It's really pretty darn good for the money. I initially bought the set to help me measure engine stuff, before I got into machining. On nice clean smooth finishes, if I do my part, it is really consistent.
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Once I figured out the anvil was rotating as I removed the mic from the piece, I changed what I was doing. After that point, I locked it BEFORE removing the mic from the work piece. Then the measurements got a lot better.
By my equipment, do you mean my micrometer, or my lathe?
Not sweating it any more. There's some semblance of consistency now. Thanks.
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They weren't, but that was fixed. 1-2" mics are harder to clean than a 0-1. For a 0-1" mic I use a sheet of paper. So I'll say the tips were cleaned with a clean kimwipe. It would be nice to make some sort of widget to clean a 1-2" mic. Using it sounds fiddly. In the mean time, I just use kimwipes.
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I did find the mic was off by 3/10ths. So I fixed that. My 0-1" mics both read 1.0000" on the standard I had (after cleaning the tips). Using the little spanner wrench, I adjusted the 1-2" mic to read 1.0000". When I put in the 2" standard, it read 2.0000". Of course, being calibrated, doesn't help with measurement technique. That's (now) just more practice.
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Don't forget about thermal expansion and contraction of a part. If you're hogging off some serious metal from the piece it'll get hot and expand. I've been burnt, euphemistically speaking, when I've forgotten to let a piece cool down before taking a final measurement and cut.
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@WobblyHand In principle, you are doing everything right. Including your comments about your practice and taking 1000s of measurements to be surer...
A couple of observations: My Mitutoyo 3-4" mic that reads to half-tents is only accurate to one and a half tenths, but is repeatable to one tenth. This is a 600 dollar mic, and I couldn't read it as accurate as your Shar's one... I believe that the Shars one is probably a little less repeatable and accurate than the Mit one, but maybe not...
I looked at your chart and you are doing fine. When doing the collar test I use a 10" bar, and locate the lathe withing .001. Most lathes, including my 3500 lb LeBlond one, can only cut to sub thou on a diameter with great care. For more accurate work I cut to one thou oversize and then lap the diameter to exact dimension. I'm sure you know that there are a hundred or so factors that affect turning the collar test below a half thousanth.
One last practice tip: buy yourself some gague pins and chuck them in the lathe and practice on them. It will increase your confidence on the feel of measuring items while mounted in the chuck, and you will know to the nearest hundredthousandth of an inch what the right answer is...
A couple of observations: My Mitutoyo 3-4" mic that reads to half-tents is only accurate to one and a half tenths, but is repeatable to one tenth. This is a 600 dollar mic, and I couldn't read it as accurate as your Shar's one... I believe that the Shars one is probably a little less repeatable and accurate than the Mit one, but maybe not...
I looked at your chart and you are doing fine. When doing the collar test I use a 10" bar, and locate the lathe withing .001. Most lathes, including my 3500 lb LeBlond one, can only cut to sub thou on a diameter with great care. For more accurate work I cut to one thou oversize and then lap the diameter to exact dimension. I'm sure you know that there are a hundred or so factors that affect turning the collar test below a half thousanth.
One last practice tip: buy yourself some gague pins and chuck them in the lathe and practice on them. It will increase your confidence on the feel of measuring items while mounted in the chuck, and you will know to the nearest hundredthousandth of an inch what the right answer is...