M&W 961b micrometer

[aeola]

I have an ebay purchase of a micrometer that given a light touch seems to give accurate results that compare favourably with my other tooling. However, firmer pressure allows anything up to a 4 thou greater measurement. Is this due to the ratchet on top, too heavy handling or is it destined to the bin because the threads are no good (on an otherwise immaculate micrometre).

Thanks for your time.

Regards,

 

[Blogwitch]

If you use the ratchet on the end of the handle, that should give you a constant reading.
Once you start to use the thimble to measure using finger feel, you will start to get inconsistent readings, as you are getting, it takes many years of practice and experience to get consistent results using 'feel', so I would suggest only use the ratchet.

John

 

[Charles Lamont]

I was instructed to use the ratchet, and to go three clicks.

 

[Nick Hulme]

I prefer the Mitutoyo smooth clutch to the ratchets, but I also find I have good enough feel to produce as good or better results without clutch or ratchet.
The ratchet allows a level of repeatability in industry that you wouldn't get with a range of people from the mechanically sensitive through to the guys who break wheel studs if they don't have a torque wrench

 

[bazmak]

I use light finger tight most of the time,but for more accurate consistant readings i use the ratchet.Most of us are happy with a thou but if working to tenths then you need a good quality mike to be used occationally.My old mike gets thrown about etc but is still within a thou.Its so old it does not have a ratchet thimble.Its a More and Wright from Victorian times probably

 

[goldstar31]

We were taught to all measure to the same set of 'Jo' blocks. If measuring something like soft rubber after grinding - you need FEEL.

I have a set - and still keep my hand in

N

 

[Wizard69]

I have an ebay purchase of a micrometer that given a light touch seems to give accurate results that compare favourably with my other tooling. However, firmer pressure allows anything up to a 4 thou greater measurement. Is this due to the ratchet on top, too heavy handling or is it destined to the bin because the threads are no good (on an otherwise immaculate micrometre).

Thanks for your time.

Regards,

This is one of those things that you can never get a good answer to on an intent thread. For example what do you mean by firmer, is that 100 ft/lbs or a few ounces of effort. In a nut shell you arbor on the micrometer needs to come into contact with the part being missed you don't want to clamp on it. In other words a micrometer isn't a C clamp.

Now that being said I find it hard to believe that you can get 4 thousands of an inch difference between using the thimble ratchet and adjusting by feel. Either the micrometer is crap or your sense of what is proper pressure when adjusting by feel is grossly off. I'm leaning towards a crap micrometer was you otherwise would have to clamp rather hard on the piece being measured to get that much of a difference in readings. Your differences in readings ought to me in tenths of an inch between using the ratchet and going by feel. You will get differences in reading but 4 thousands is so much that I have to believe something is wrong.

Gooldstar alluded to the use of Jo' blocks to learn how to use a micrometer. This is good idea as the cases are lapped very parallel so that is one less thing to have to deal with. You should be able to run the micrometer with the ratchet and get repeatable readings every time. The same thing as by doing it via touch on the thimble. The two sets of reading might not agree but each set should be repeatable, if not something is wrong and will need to be addressed. The only thing you really need to watch for is heating of the micrometer or the Jo block, hot micrometers or Jo blocks will cause readings to drift a bit.

 

[nautilus29]

I would maybe test the mics out by securing them in a vice with protective jaws and putting an indicator on the moveable shaft. Zero out your indicator and without spinning the mic see how much play you get when you push and pull on it. That should show you if there is really 4 thou play in the threads. Do this with the mic in different locations as the threads could be worn in one spot and not another.

If you calibrate your Mic to the ratchet, and the mic isn't junk, you should be ok. I've never liked ratchets on mics though the slip fit style seem to give more consistent results from mic to mic. The ratchet style never seems to be a consistent from mic to mic which means you have to get a feel for every mic you use. You can also get a different ratcheting pressure by how fast you turn the ratchet. If you turn it slowly you will get more torque on the mic before the ratchet slips compared to if you ratchet faster. And likewise if you ratchet really fast you can get a different result.

Adding to what goldstar said I would also practice using the mic on a dowel pin too as the feel is a little different then on flat stock. Practice with the mic till you get consistent readings and then calibrate it to that feel. Then you just have to be consistent with that feel Everytime you pic up that mic.

 

[Nick Hulme]

Do this with the mic in different locations as the threads could be worn in one spot and not another.

And if it's the same everywhere it isn't worn, the thread clamp under the barrel simply needs tightening to eliminate the play, if you take the barrel off to adjust the thread clamp you can re-fit the barrel with the zero line positioned as you require. ;-)

- Nick