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Thread: Caliper/Micrometer Questions...
03-13-2005, 02:02 AM #1
I'm in the market for a new caliper and micrometer.
Possibly an Etalon 260 micrometer, and maybe a Mitutoyo digital caliper? Not sure yet.
Anyhow, could you guys tell me the difference between:
Friction and ratchet stop micrometers? I see there are also a few that are both friction AND ratchet stop.
Trying to decide which is best for me, and what the advantages/disadvantages are of both.
Also, with the digital micrometers/calipers, I see some say SPC output, "YES" or "NO". What does SPC stand for?
I won't get into recommendations on different brands, as I know that has been beat to death, but I would like to ask if you guys feel digital is MORE, LESS or the SAME accuracy as the old standard type?
03-13-2005, 03:56 AM #2
Paul -- As a practical matter, the quality of the mic is more important than the friction vs. ratchet question. The ratchet type can have a slight "impact wrench" effect, overtightening the mic in some hands. However, that's more important in a manufacturing setting where many different operators will be using mics and the plant wants to eliminate differences in "feel" between operators. In that case, and where tolerances are tight, a good friction style might be best. For your own use, find what feels comfortable to you.
SPC stands for Statistical Process Control. Calipers so equipped have an output that can be plugged into a display and/or device for logging repeated measurements and calculating variation.
Good mechanical and digital calipers are about the same accuracy in my experience. Not sure about digital mics. I've used the Mitutoyo, Starrett, and Chinese digital mics and would rate them in that order, with Mitutoyo and Starrett near equal, the and Chinese digital mic significantly worse. The cheapest digital mics and calipers are less accurate than their cheap mechanical counterparts in my experience. In other words, I'd be more inclined to trust a cheap import vernier caliper or mic at around $15 than the electronic ones at around $25.
03-13-2005, 04:46 AM #3
I might have a line on some stuff you'd be interested in.
03-13-2005, 06:56 AM #4
For a 1" mic I prefer the friction. When holding and measuring small parts, I can hold the mic and work the thimble with one hand. The larger sizes this gets harder to do, but I still prefer the friction thimble. I guess having all your mics the same style helps maintain consistent "feel". When brand shopping, I look at the graduations. Some brands/models are easier to read than others.
03-13-2005, 08:37 AM #5
My favorite dial caliper is the first one I ever bought. It came from the Craftsman catalog in the early 90s and was obviously made by someone else but I don't know who.
The happiest feature is that it is an 8" caliper. That length feels very balanced in my hands.
Having said that I've used the classic Starrett 6" and 9" mechanical dial versions and while they are fine instruments I would still take the old 8" due to the balanced feel.
The electronic versions are wonderful if you run across a mixed bag of USA and metric measuring needs. Sometimes I'll put a caliper to a shaft and get an oddball inch reading, then switch to metric and it comes out to xx.00 mm and there you have it with a minimum of frustration.
Once I got above 2" I went to a place called "Re-Tool" and got 3" and 4" mics used. They were something like 19.95 each for used Starrett and Mitu. A little dirty with strange paint jobs and engraved initials. But the leadscrews are smooth and the anvils are not nicked or badly scarred.
My thinking is that I don't do any home shop work in that range to the international standard. Otherwise said, all my work is comparative, i.e. fitting parts measured with the same micrometer. I have no expectation that 3.012" as measured on my old mic will read the same on someone else's carefully calibrated version used by gloved hands in a temperature controlled room.
I DO expect, however, that when I set out for a .001" interference fit on a 4" OD tapered roller bearing race that it comes out right. I've measured the telescoping gage and the bearing OD with the same mic.
03-13-2005, 10:41 AM #6
I was so impressed with the quality and the ease of calibration of a Polish made no-name 0 - 4 mike set I bought from Enco as a present for my nephew, I bought a 0 - 12 set for myself and acouple more 0 - 4 set for gifts. They feature carbide faces, friction thimbles, cast iron frames above 4", satin chrome, axial adjustment on the thimble, and all the other featured found in the better quality mikes.
I sent a couple of them through a bootleg calibration and they aced all the tests for spindle face run-out, spindle face/anvil parallelism, flatness, measuring screw lead, and so-on. These are the Enco mikes made in Poland and they still sell them but the price has gone up a little in 5 years.
Enco also sells a Chinese made line of mikes for about 1/2 the price but I wasn't too impressed with the ones I've handled. For one thing I don't like friction thimbles (personal prejudice). For another they didn't have an axial adjustment for the thimble.
Be sure to ask for the country of origin regardless of who you buy them from. Not that the country actually makes a difference but Eastern Europe was the tool maker for the old Soviet Union and they're in the same business today.
03-13-2005, 11:04 AM #7
i'll second the polish mics ... i use a b+s 1",
and my 2,3,4,5" mics are the Bison-made VIS
brand...not much diff... the VIS are 1/2 the price
of the B+S mics and feel almost as sensitive
and smooth(probably'd be closer , but i don't use
the larger mics as often.
as for calipers, i won't touch anything but my
Mitutoyo 6" digimatic , mauser 9"vernier ,chinese
12" vernier. no mechanical calipers in my shop...
03-13-2005, 12:11 PM #8
3rd that on the polish mics/friciton thimbles. Have had a set thru 7" for about 20 years. Gave away my Starretts over the years, have a few Mitutoyo specialty mics (spline, reduce diameter anvils, extended reach)
03-13-2005, 02:54 PM #9
Could someone tell the difference between friction and ratchet? Is it just the type of "action" used inside?
That's all I would like to know. Thanks so much for all the info fellas. You guys are great!
03-13-2005, 04:28 PM #10
what you refer to is a device stuck on the end of the thimble which limits the torque applied to the spindle. ratchet or friction is a matter of preference, but all it does is help you to maintain consistant readings from
part to part. i tend to prefer a rigid thimble
on my mics-
03-13-2005, 04:52 PM #11
Both the ratchet and friction devices aim to apply a consistent torque (and thus, more or less, pressure) to the anvils.
The ratchet type has a pair of stair-stepped cams which operates against spring pressure. It comes off the cam with a "click" and many operates count the number of clicks for consistency.
The friction type often has a sort of coiled spring clutch which grips inside the thimble. There are many variations on this theme -- some better than others. Again, the idea is that it will slip at the same torque every time.
03-13-2005, 05:17 PM #12
Well it looks like many of you prefer friction. I will probably try those to begin with.. Thanks fellas.