Brown and Sharpe 252 Adjustment

[JohnC]

I have acquired a Brown and Sharpe 252 internal micrometer. This is a very nice item, very smooth and in good condition. However, I can see no way of adjusting or calibrating the device. There is no hole for a c spanner to rotate the lubber line, as on similar micrometers. There is what appears to be a stamped figure Z or 2 adjacent to the fixed anvil, and a screw with collar on the end of the barrel. The moving anvil is a good fit on its shaft, secured with a grub screw, but with no obvious sensitive adjustment.

Does anyone have experience of this model that can point me in the right direction to correctly zero the reading? Many thanks in advance, John

 

[Blogwitch]

I am sure you know that if the setting ring is missing that you can use an external mic for setting it with.

Is the fixed anvil 'slideable' ? If so maybe that is the way to do it.

All my later internal mics have an adjustment hole as can be seen on the pictures on here.

http://www.arceurotrade.co.uk/Catal...ometers/Inside-Micrometers/Inside-Micrometers

Click on any of the pictures to see a larger image.


John

 

[JohnC]

Hi John, Thanks very much for your reply. As far as I can see, the set up is as follows: the thread inside the graduated thimble engages with the thread in the body with the fixed anvil. So their relationship is fixed. There appears no way to turn the lubber line relative to the thread in the body. The rod that moves within the body is driven by the shoulder against the inside of the graduated thimble - again this relationship is fixed. The hole at the end of the thimble is a sliding fit on the narrow portion of the graduated rod. The threaded washer and dome nut merely adjust the backlash. So unless I am missing the blindingly obvious, I can see no way of setting the mic except altering the position of the moving anvil on the rod - which seems a bit crude!

 

[DJP]

Perhaps there is a missing set up gauge. Some fixed gauge that you use to zero the jaws while honing them. This sounds crude too but the other option is to add it you a museum collection. I have a few old measurement tools that are headed to that destination. Digital read out is so much easier for old eyes as long as there are batteries available.

 

[Blogwitch]

John,

If I could make a suggestion. But first do a check to see how far out it actually is using an external micrometer.

Get a couple of pieces of wood, put them together and drill through them with the same size drill as the tube, just like a split bearing, then shave a tiny amount of wood off each part.

Clamp down on the two pieces in a vice and try turning the fixed jaw. I am sure it must rotate, as all mine do using the little pin spanner. The joint between the jaw and tube must be a very slight interference, and besides, you only ever need to adjust them every blue moon.

John

 

[JohnC]

Thanks John, I will give that a try,
John