Need help zeroing an old style M&W No.961SB 0-1"micrometer

Hi,

I've inherited my grandfather's 0-1" micrometer (an older style M&W - model No.961SB) and am trying to adjust it to get rid of an error of about 3/10 of one thou that's showing-up when zeroing.

If I'm understanding the adjustment technique correctly, then I should be trying to use the spanner with the small pin to rotate the sleeve by the required amount - only problem is, the sleeve doesn't want to move and the hole that takes the pin of the spanner is elongated (worn?) meaning that the pin keeps slipping out.

If anyone can offer advice on a way around this, I'd be very grateful.

PS: I know that the 'B' on the end of the model number means the micrometer is graduated in tenths-of-a-thou, but what does the 'S' stand for?

Cheers

Anthony

Hi

Soaking it in penetrating/release oil a few hours may help.

Nige

Best check that error's constant by checking with a couple of items with accurately - known dimensions. If the error varies, and you can't bring it constant by adjusting the thread collar if there is one, the mic's' effectively worn out. That does happen.

Post deleted

Edited By Clive Brown 1 on 04/10/2017 10:42:01

Edited By Clive Brown 1 on 04/10/2017 10:44:34

Sometimes those adjustments have corroded or tightened so much that they are immovable on old micrometers. The elongated hole supports this. You could try holding the barrel in a vice, with brass packings to prevent damage, then applying leverage to the curved part. Bit of a last resort though. Definitely try the penetrating oil first.

Noo, don't risk crushing it in the vise - make a bored holder same diameter as the tube, with a slit along the length. Use this for holding the tube in the vise.

That's a much better idea. Or wrap it in a few turns of thick brass shim and hold it in the 3-jaw.

Go easy with gripping the sleeve, the slightest distortion makes for a very tight thread and that's the end of a good mike!

If the sleeve can't be freed, it might be possible to adjust the zero by unscrewing the ratchet. One end of the M&W spanner fits the flats. This releases the thimble from the spindle, which push together, and allows resetting of their relative positions. It's a bit of a fiddle but does work, on mine anyway.

Alternatively, put up with the zero error!

I was taught that the method of coping with a zero position that was a few thou out was to note the 'error' and then add (or subtract) the error from any measurement. Experience shows that adjusting the barrel (sleeve) may work for today, but next week it will once more be not quite zero.

Cheers, Tim

I had the same problem with an old Ambrose Shardlow micrometer.

I removed the spindle/thimble then gripped the sleeve in a collet (which gave an all round equal grip) mounted on my lathe and simple rotated the micrometer frame by hand . It did not take much force to get the sleeve to move. You may have to reassemble the mic. a couple of times to establish the required zero position.

On no account attempt to grip the sleeve in a bench vice or a 3 jaw chuck as the sleeve has only a very thin wall thickness and can easily be distorted.