Help me shop for a micrometer gauge
March 25, 2022 4:57 PM Subscribe
I need to replace a 0-1" micrometer with 0.0001" divisions. (Could also be metric.) Can you help me decide how much to invest, and maybe help me find a reliable and not-too-expensive source?
For a Physics 102 experiment, my students need to measure the thickness of waxed paper. This year I got out our box o' assorted micrometers and they were all rusted, broken, or rusted and broken. (Og only knows how they all got so rusty. I will try to find a non-humid place to store their replacements.) There are occasional other reasons to use micrometers, but this lab is the main use.
I have not had to buy this kind of precision measuring tool before, and I'm having a hard time figuring out how to satisfy our needs. If you measure the thickness of small things, please lend me your experience! Do you have a favorite workhorse micrometer to recommend? How much should I plan to spend, and can you recommend a reliable seller who has fair prices?
Based on googling around, it looks an entry-level model costs $50, and I'm guessing the ones at Taylor and Fisher Scientific are the same low quality but overpriced at $75. At sources with actual grownup tools, $100 seems like the lower margin for a decent one, but they go up to $400-ish. I don't know the reputation of any of the big tool websites that I'm finding, though.
There are some drastically cheap ones with not-uniformly-terrible reviews listed for $25 on Amazon. For this experiment, at least, precision/accuracy is not extremely critical, so it's mighty tempting to buy a classroom set of 8 for $200 and gamble that at least some of them will turn out to be serviceable.
On the other hand, trying to learn a new skill like reading a Vernier scale on a junky instrument can be frustrating, so maybe it'd be better to get a couple of $100 ones to share between the lab tables. And hopefully the students won't figure out how to break those after a couple of semesters. Or will one in the $150-$200 range get me significantly improved durability and ease of use?
For a Physics 102 experiment, my students need to measure the thickness of waxed paper. This year I got out our box o' assorted micrometers and they were all rusted, broken, or rusted and broken. (Og only knows how they all got so rusty. I will try to find a non-humid place to store their replacements.) There are occasional other reasons to use micrometers, but this lab is the main use.
I have not had to buy this kind of precision measuring tool before, and I'm having a hard time figuring out how to satisfy our needs. If you measure the thickness of small things, please lend me your experience! Do you have a favorite workhorse micrometer to recommend? How much should I plan to spend, and can you recommend a reliable seller who has fair prices?
Based on googling around, it looks an entry-level model costs $50, and I'm guessing the ones at Taylor and Fisher Scientific are the same low quality but overpriced at $75. At sources with actual grownup tools, $100 seems like the lower margin for a decent one, but they go up to $400-ish. I don't know the reputation of any of the big tool websites that I'm finding, though.
There are some drastically cheap ones with not-uniformly-terrible reviews listed for $25 on Amazon. For this experiment, at least, precision/accuracy is not extremely critical, so it's mighty tempting to buy a classroom set of 8 for $200 and gamble that at least some of them will turn out to be serviceable.
On the other hand, trying to learn a new skill like reading a Vernier scale on a junky instrument can be frustrating, so maybe it'd be better to get a couple of $100 ones to share between the lab tables. And hopefully the students won't figure out how to break those after a couple of semesters. Or will one in the $150-$200 range get me significantly improved durability and ease of use?
Best answer: My father who was a physics professor gave me a micrometer a decade ago.I saw your post and went to check its condition.It’s in good shape.I can give it to you. Memail me.
posted by SunPower at 6:16 AM on March 26, 2022 [1 favorite]
posted by SunPower at 6:16 AM on March 26, 2022 [1 favorite]
Best answer: Make calibration of accuracy and distribution of error part of the exercise, and get 8 of them for $200. You can do a pretty good job with crappy instruments if you know what to expect. Get some metal shim references to support this effort.
After fully characterizing these cheap instruments, have them apply this new knowledge to measuring the thickness of waxed paper.
posted by the Real Dan at 1:24 PM on March 26, 2022 [1 favorite]
After fully characterizing these cheap instruments, have them apply this new knowledge to measuring the thickness of waxed paper.
posted by the Real Dan at 1:24 PM on March 26, 2022 [1 favorite]
Best answer: the Real Dan has a fantastic point that also makes good use of money. It's an experiment of not just accuracy and precision, but of distribution of error.
In high school we did the Milliken oil drop experiment. Everyone in class had what seemed like random numbers, and random numbers across a broad range. Throw all the results together in a big pot and stir statistically, and we got multiples of a very precise number. Wow, that's a mind bender first time you see it!
Also "Mitutoyo" typo above, though the link is correct. And Mitutoyo is a great bad habit into the world of measuring precisely and accurately. :)
posted by lothar at 3:52 PM on March 26, 2022
In high school we did the Milliken oil drop experiment. Everyone in class had what seemed like random numbers, and random numbers across a broad range. Throw all the results together in a big pot and stir statistically, and we got multiples of a very precise number. Wow, that's a mind bender first time you see it!
Also "Mitutoyo" typo above, though the link is correct. And Mitutoyo is a great bad habit into the world of measuring precisely and accurately. :)
posted by lothar at 3:52 PM on March 26, 2022
Best answer: Get the 8/$200 deal. I'm a manufacturing engineer and MSA (measurement systems analysis) is my bag. The gold standard for a gauge R&R study is 10 parts measured 3 times each by 3 operators (total of 90 measurements). You can crunch that data (Minitab has a specific wizard for this, but Excel will work. Or do it by hand.) and see how good your students are and how good your micrometers are. Less than 10% is great. Over 30% is bad.
Reading a Vernier scale is frustrating at first, but easy once you do it a couple times. I wouldn't spend the extra money on a digital version. We have some 20+ year old Vernier mics that get calibrated 4 times a year at a NIST lab and their "as found" condition has never been out of tolerance.
posted by spikeleemajortomdickandharryconnickjrmints at 4:06 PM on March 26, 2022 [2 favorites]
Reading a Vernier scale is frustrating at first, but easy once you do it a couple times. I wouldn't spend the extra money on a digital version. We have some 20+ year old Vernier mics that get calibrated 4 times a year at a NIST lab and their "as found" condition has never been out of tolerance.
posted by spikeleemajortomdickandharryconnickjrmints at 4:06 PM on March 26, 2022 [2 favorites]
Response by poster: Thanks all for the info! I don't think that the 102 students would, uhm, enjoy the exercise of testing out all the micrometers... but the students in Advanced Lab or Engineering Design would be into it!
And, wow, SunPower, how generous of you! Thanks! It will be good to have a really nice tool tucked away on a high shelf for more critical measurements.
posted by BrashTech at 5:43 AM on March 27, 2022
And, wow, SunPower, how generous of you! Thanks! It will be good to have a really nice tool tucked away on a high shelf for more critical measurements.
posted by BrashTech at 5:43 AM on March 27, 2022
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Most of my measuring tools are eBay finds... good used oddball/expensive flavors can be had at ~30% of new. I lean toward Mitutoyo & Starrett brands. A quick eBay search for "non-rotating disc face" includes these 2 Fowler 0-25 mm Non-Rotating Spindle Disk Micrometer 52-251-025 that have the resolution you want.
posted by tinker at 8:09 PM on March 25, 2022 [2 favorites]