Vernier vs Micrometer

[TerrydParticipant @terryd72465]

Posted by Steve Garnett on 28/01/2012 00:05:51:

Posted by Andrew Johnston on 27/01/2012 19:26:46:

 

 

I was under the impression that the early Mitutoyo digital calipers used two optical gratings at a slight angle to each other. So the Moire fringes were a true optical effect and nothing to do with verniers. Of course I could be wrong.

 

I don’t know – I’ve never been able to justify buying any of Mitutoyo’s calipers!

 

But along those lines, there’s one more interesting patent from 1987, which uses the word Vernier in the title, and works on both rotary and linear scales. Much clearer to understand, too.

 

US Patent 4,654,524

 

Hi Steve,

 

That is a vernier system and of course the petition is much easier to read and comprehend the underlying theory.

 

Best regards

 

Terry

[TerrydParticipant @terryd72465]

Posted by Wolfie on 27/01/2012 16:53:44:

Oh man don’t any of you lot give up the day job

Anyway I spent this aft cleaning the old thing up and its come up OK. Its a Moore and Wright and my mam reckons it was my granddads. And being as he’s been dead for nearly 30 years its probably laid there all that time. Looking at Terrys handy photos I have a 1″ micrometer in 0.001 increments.

It cleaned up OK but its stiff-ish especially in the lower half inch and I can’t use the little ratchet thing to turn it. The faces look ok and square. Also it has some kind of deposits on the outer barrel which make it a bit difficult to read. You can see them in the pic, a sort of dark mottling.

 

Incidentally I checked it out against my digital vernier and the vernier was within half a thou every time.

Edited By Wolfie on 27/01/2012 16:55:57

Hi Wolfie,

 

I hope I’m not being too obvious, but the knurled ring in the cutout in the frame is a locking ring. Have you tried twisting that? Looking from the ‘Anvil’ end it turns clockwise to free it. The micrometer can be cleaned, adjusted and re-set, it is not complicated as they are quite simple instruments.

 

Inside the ‘barrel’ is a spindle with a screw and nut which adjusts the amount of play and stiffness of it. Here are some pictures and instructions. There is a special spanner provided with each micrometer to do this work. It is usually kept in the ‘spectacle case’ that the micrometer is provided with, basically a small ‘C’ spanner.

 

Regards

 

Terry

[Gordon WParticipant @gordonw]

Wolfie, you can clean it up no problem, when you get it right try and find somebody to show you how to hold it when in use, ie. one handed. Also try not to use the ratchet at the end, they are more trouble than they are worth. Try to get a feel for it, it will all come .

[WolfieParticipant @wolfie]

Yes I discovered the adjusting nut and also the locking ring. It seems to be the locking ring thats the problem. Without that in its very smooth.

 

I’ve had it to pieces and liberally added clock oil and worked it. The piece that screws right out doesn’t seem to come apart apart from the clicky bit at the top.

 

The biggest hassle is the discoloured barrel can hardly read it in places

[TerrydParticipant @terryd72465]

Posted by Wolfie on 28/01/2012 11:13:17:

Yes I discovered the adjusting nut and also the locking ring. It seems to be the locking ring thats the problem. Without that in its very smooth.

 

I’ve had it to pieces and liberally added clock oil and worked it. The piece that screws right out doesn’t seem to come apart apart from the clicky bit at the top.

 

The biggest hassle is the discoloured barrel can hardly read it in places

 

Hi Wolfie,

 

at least you have a nice heritage piece in memory of your grandad. New ones aren’t too expensive and are quite accurate due to teh way they are made and the basic screw concept. There are usually loads on eBay as well.

 

Best regards

 

Terry

[Ian S CParticipant @iansc]

Got a 0 to 1 mike here that I bought for 2/6 back in 1962, it’s a DCMT, as avertised in Model Engineer of the time, and before, it’s simple, no lock, no ratchet, and the adjustment is via a screw under the fixed anvil, but it seems quite accurate. I bought it at about the same time as I bought my Super Adept lathe. Since then I have got fancier mikes Starret, and Mitutoyo, and a 50 to 75 mm Russian one from a second hand shop. The Russian sailors sell just about anything on their ships that can be moved, its a wonder they manage to ever get home. I do have a 150 and a 200 mm digital calipers, and one thats quite handy for rough jobs, columbus gauge/ calipers, looks like vernier calipers but much cheaper. Ian S C

[The Merry MillerParticipant @themerrymiller]

Ian, I have two of the DCMT mikes been languishing in my tool cupboard for centuries.

 

I did consider chopping them down and using the barrel sections as a micro stops on the Myford, this I still may do.

 

Len. P.

 

[Peter G. ShawParticipant @peterg-shaw75338]

Billy,

 

Yes a NPL certificate would be nice – at least then I’d have some idea about it’s calibration!

 

Seriously though, yes I am aware that they don’t necessarily switch off – there is an internet article somewhere about this in which Mitutoyo came out best by a long way in this respect.

 

What I do NOT accept is that the degree of variability is not consistent, ie the Aldi digital caliper gives varying readings both plus & minus of nominal such that it is impossible to interpolate with any hope of being anywhere near. The Rolson digital caliper is incorrect but more or less linear which means that it is usable as long as the user is aware of the discrepancy.

 

Taking the battery out is what I now do, but lets face it, even the given specification of the Rolson digital caliper is somewhat poorer than the Starrett dial caliper yet both have the same nominal resolution and capacity. Hence, given the problems of inserting/removing the battery together with the poorer specification means that for this rank amateur, “manual rules OK!”

 

Regards,

 

Peter G. Shaw

 

[Martin WParticipant @martinw]

Hi

 

While browsing I found this site that sells callipers, micrometers etc from the bargain basement range to stuff that costs more than my lathe. They have kit with a resolution of 1 micron/accuracy 2 microns at very reasonable prices. So if its accuracy you want then not a bad place to start, usual caveats re interests etc.

 

Martin

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