Which outside micrometer? (Mitutoyo, probably)

[Cyclotronguy]

As an old machinist from a family of old machinists and way too many micrometers; for casual use I'd pass on carbide faces. In casual use it's too easy for the carbide to chip.

The garage guy is never going to wear out a standard spindle and anvil. I've got my grand dads Brown and Sharpe 13 (0-1") stainless steel, he bought it in 1948. It made dredges for Yuba Mfg, till he retired. It was my beater in industry for 30 years, it's still my daily carry and it still wrings to better than 0.0005 on gage blocks anywere in range

 

[Cyclotronguy]

Early on someone made reference to the vintage Etalon mic.... they are lovely.

The imperial reading one come in at 1/2 thou per division on the thimble so you have to pay attention

New they are ghastly expensive, best new mic at a reasonable price point AFAIK are Mitutoyo, I think them a cut above Starrett. There are some great used mics to be had on Ebay, Craigslist and etc.

 

[troked17]

What’s the difference between ratchet, plain, and thimble? Especially the meaning of the word thimble wasn’t clear from the Mitutoyo website.

Doesn’t the appropriate force depend on the object being measured? Measuring the diameter of a cylinder would require less force than measuring the thickness of a shim. Measuring the diameter of a ball would require even less force (almost none, I guess). So can the constant-force device be adjusted?

If it matters, I think I have a fairly good mechanical feel and understanding (for a hobbyist mechanic, not for an experienced machinist I’m sure).

Different types of thimbles. Mitutoyo offer these within 293 micrometer range. For example, 293-185-30 has got the ratchet thimble.

 

[cannuck]

One use I have in mind is to compare the dimensions of new and worn parts of machinery to see the effect of different lubrication regimes. However, I don’t know how much precision is needed for that, not having done this kind of thing before.

For example, new bicycle chains have a pin-to-pin distance of 0.5 inches (Shimano tried a metric 10 mm pitch chain a while ago, but thankfully the market wasn’t interested and the half-inch standard has remained). A chain is considered worn out when wear of the pins and bushings causes 1/16" of elongation over 12 inches of chain (24 links). I’d like to find out how much of that wear is at the rollers and how much at the bushings, and possibly compare those values for different manufacturers’ chains.

Having a bit of experience in tribology, I can say that one thing a micrometer is NOT going to do for you is measure most failed or some worn cylindrical surfaces. IF they are worn consistently, then you will be alright, but reality is they usually wear in some taper and fail with grooves - and the relatively large flat anvil of a mic is just too big. Even a really good digital caliper usually has a fair flat spot on its ground measuring tips that won't go into grooves of small wear surfaces. If this is what you encounter, you need to go into optical comparitors, profilometers or even SEM to get a good picture of wear scars.