Mitutoyo Mic question

I just bought a mitutoyo 0-1 inch micrometer model 193-211 off ebay.
It looks pretty good but when I go to snug it up for a measurement, the knob sort of slips like it has a clutch so you can't make it too snug. Is this normal or a defect?

Thanks

Rich

Sounds to me like what you have is a friction thimble micrometer. It's a good thing.

Yeah, friction thimble, if it goes click click click, ratchet thimble. Makes them a little harder to use as C-clamps.

I hate them, on small mics anyways, heavy, throws the balance off and feels wrong in my hand. Very good things on large mics.

Also a good thing for ham fisted monkeys. AKA "operators". Though they will still screw it up. Also good to get repeatability
between operators.

Not a bad thing, I'm just practicing to be a cranky old bastard, so I don't like it.

Thanks guys
Friction thimble it is.
Next question: Is the friction changeable or is it set for good?

There is a coil spring inside that could possibly be changed or shimmed,but why? There is still part of the thimble that doesn't slip.
On a B&S the rotating barrel part can be flipped over and will no longer slip, likely so on the Mititoyo.

Dave

They are a mixed blessing in some ways. It takes slightly more pressure to get an accurate measurement across flat surfaces than on say the diameter of a bar.

One partial way round that is to clean the anvils and the work rather thoroughly each time you use it. You should clean the anvils on a mic regularly anyway. The easiest way to do that on a 0 to 1 is to grip a piece of paper using the ratchet and then pull it out. Then check the zero again and it sound like some may be surprised how far it will shift even if there was only a tiny trace of oil on them.

John

lectrician1 said:

Thanks guys
Friction thimble it is.
Next question: Is the friction changeable or is it set for good?

Click to expand...

Why? The friction is set as a standard so that a different micrometer will give the same measurement. Surely if you change the friction the readings will not be as accurate

geoinc said:

Why? The friction is set as a standard so that a different micrometer will give the same measurement. Surely if you change the friction the readings will not be as accurate

Click to expand...

Yes and it wears. That's another reason why they are a mixed blessing and why ratchet on the end is a much better idea really.

John

Are you implying that the ratchet does not wear?

Any change to the friction or ratchet will be calibrated out when you set it via the standard (or 0 for a 0-1.) Only important thing is that it stays consistent since last time you set it to the std.

I suspect you are some one who isn't used to using a mic in realistic circumstances. Basically ratchets are great for people who can't use a mic properly and also for those that never have their work checked by some other method and never really attempt high precision work. It's a fact that when measuring the diameter of a bar as against 2 parallel surface there can be up to and even over a thou error. Or even more if say the mic is used to measure across telescopic gauges that have been set to a bore.

The best way to learn to use a mic is to find some slip gauges and a plug gauge that has been accurately made. Clean everything thoroughly including the mics anvils and measure them. Worse still use the mic for a while and then go measure them again. They never stop clean which is makes things even worse. Ratchets will show a thou difference just on the basis of how fast they are turned. In fact some use that for feel.

Some one with real experience tends to use the feel aspect of the mic to ensure that fits finish up in the right direction as well.

All a bit more difficult to do with thimble ratchet mics. One of my worst in that respect is a 1 - 2 by 1/10th, another is 25 to 50mms by microns. In both instances I couldn't get one with the ratchet on the end so have to use the main barrel of the mic.

John
.

I personally don't use the ratchet end, I do it by feel. I feel it is more consistent as the ratchet will start to spin when it is out of alignment, but with feel I will feel that it is out of alignment and not just assume that it is good. I would say I can get less than a tenth repeatability even on large parts. But it takes a bit to work out the feel and someone having the patience and spending the time to teach on what to feel if you haven't had the experience.