dirty metric fudge

[brian jones 11Participant @brianjones11]

Having seen the cost of metrifying a combo slide £190 for the kit. I thought of a quick cheat which comprised making a suitably scaled label on cad and sticking around the rim of the micrometer head.

now Im sure this must have been done before, so apologies if this is old news.

You measure your rim – 36.7mm and make a label divided into 25/25.4 x 36.7

I made my divs 0-1.25, with the black scale counting up towards the work and also counting up red scale away from the work

I made the dial resettable as well – another story

The reason is that combo slide micrometers are normally used for close finishing cuts. So reset the dial to zero and proceed as desired

I checked the dial for 1mm against a dial gauge and it was spot on

Of course ther is a small gap between start and finish of the scale but its liveable, its not an absolute dial, its relative

I also thought I might make the cross slide with 2x unit scale so that it read diameters instead of radii so 1mm in becomes a 2mm diameter reduction

Is that confusing?

 

apologies for the scale pic is was a trial, I will get a better pic but you get the gist

Edited By brian jones 11 on 06/07/2021 17:14:07

[brian jones 11Participant @brianjones11]

[Pete RimmerParticipant @peterimmer30576]

With 10TPI screws you could make your dials dual-reading. 0.1" pitch is 2.54mm so you could print dial scales with 100 divisions for imperial and 250 for metric then the metric scale would only be off by 0.04mm/turn (1.57 thou). Less than the error in a well worn cross slide screw.

Some Denford lathes do exactly this.

[brian jones 11Participant @brianjones11]

Indeed a good point, but i didnt want to post this for being shot down by hardliners who demand precision

I will post some pix of labels which can be scaled to suit, or anyone with cad can make their own

there are of course cases where a 1.57 thou error is unacceptable eg shaft fitting a bore. if its over it wont fit or else be loose.

personally i prefer to know exactly with my fudge but in the agricultural world …………….

CNC world works at micron level – scary

I am trying out my simple fix for an adjustable micrometer dial (after all a dial gauge has one) but space is very limited and I am trying to keep it simple

Any one else been there pls pitch in

[Nigel Graham 2Participant @nigelgraham2]

I would not call it a fudge.

The important point is that you know its limits of accuracy (or precision – not a synonym but I can never remember which is which!).

[GeorgineerParticipant @georgineer]

Posted by Nigel Graham 2 on 07/07/2021 11:14:02:

… The important point is that you know its limits of accuracy (or precision – not a synonym but I can never remember which is which!).

[Colin WhittakerParticipant @colinwhittaker20544]

At my old company a nuclear logging expert was giving a presentation in South America to an oil company on the accuracy and precision of a downhole measuring instrument. The prentation employed a simultaneous translation into Spanish but was not well received with lots of bored and/or bemused faces.

A post mortem revealed that the simultaneous translator was using the same Spanish expression for both precision and accuracy!

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