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Long arm off height gauge = crude repeat o meter?

lucky7

Titanium
Joined
Sep 6, 2008
Location
Canada
Theoretical question- if a guy knew his height gauge had a very good bottom for flatness without rock, could he get similar info with a long stiff arm extended in front of it and a dti with ‘enough’ sensitivity on its end as you’d get with a Rahn repeat o meter?

L7
 
Why not make a repeat-o-meter clone? The r-o-m sets on three discrete points, and measures a 4th point. Any deviation of those 4 points shows up on the indicator. You have to do some moving around to figure out which point is actually causing the deviation. I think the r-o-m is less likely to be influenced by local slopes in the plate than a solid contact surface.

Now all you need is a 10 microinch resolution on an indicator.
 
One of these days I will make a repeat-o-meter clone. But I'm going to do something like this (from Robin Renzetti)

ULTRA PRECISION REPEAT O METER - YouTube

This is simpler to make than the original, and uses an LVDT-based electronic sensor. I happen to have one of these in the cupboard - a Mahr Millimar - which I will use for that.

A similar device is a shop-made spherometer, again made using an LVDT-based sensor (this is from Tom Lipton, Oxtool). You can see that in action here, starting at 16:48 in:

Making Flat lapping plates 3 - YouTube

There's a lot of cool stuff on YouTube these days.
 
It would work just the same.
I would set the arm up so that the dti is the same distance out as the base is long so you don't have to worry about a exaggerated reading and use a parallel block (scrapers block) to even out the surface a bit
 
Why not make a repeat-o-meter clone? The r-o-m sets on three discrete points, and measures a 4th point. Any deviation of those 4 points shows up on the indicator. You have to do some moving around to figure out which point is actually causing the deviation. I think the r-o-m is less likely to be influenced by local slopes in the plate than a solid contact surface.

Now all you need is a 10 microinch resolution on an indicator.

I have a mitutoyo 1um drop indicator. :)
 
I have a 0.0002mm indicator from Aktiebolag CE Johansson
But the needle is so thin you hardly notice it when it passes
Never had the need to use it so probably not functional any more

Peter
 
I notice the link Street provides only sells 20 microinch indicators, where a 10 microinch indicator is required for plates under about 16 sq*ft. The specification requires at least 5 graduations within the r-o-m tolerance.
 








 
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