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High accuracy angle measurement


Jan 14, 2007
Flushing/Flint, Michigan
Decent optical compartors are not cheap and take up floor space.
Even if you get a 20 or 32x guy cheap you need the 50 or 100x lens and those .. :willy_nilly:price tags.
Optical compartors use collimated light and a semi-telecentic lens to increase the depth of field and allow you to do rounds.
Any decent one will have a adjustable stop on the light source. Many also have a color filter (often green) that helps the imaging lens.
Stop it down, toss in the filter and you need some real serious lighting power at 100x.

Toolmaker scopes don't use up so much floor space, can be found for $1000 and you can stick a camera on them for easier use but you sacrifice resolution compared to a human eyeball. Same as with a compartor, if you move to make measurements using the readouts the stage has to be so dead nuts on.

The sine plate/bar and a 50 millionths DTI is not a bad idea if you can trust the nose flat to be true(90) to the shank. I do like this.

Once you get into this high mag optical or video you get to instantly see the surface finish problems if the part comes off of a lathe.
Also think that in the measuring/making world there is the "rule of ten".
Take your tolerance allowed and divide by ten. Can I repeatably check to that?

I'd file this under a bit hard to check but not the crazy world.
Can the customer actually check it and do they want you as a new vendor? Sometimes the PA sends out jobs and others do not like a change.
Try to tell the customer that their measuring is for shit. :eek:
End game is happy customer no matter what.
Last edited:


Oct 1, 2013
Rochester, NY, USA
Here is my take:
-Best (simplest) way is to use a set of go, no go gauges , looking for light coming through the gap. This does not give you a quantitative measurement though.
-An optical comparator may let you measure directly, some have 1 minute of arc resolution on the rotating screen protractor. 1000x magnification doesn't help much; for a 0.1 inch leg you need a 100" screen.
-Measuring on any x-y device is possible; the tolerance ( 10 minutes of arc) is 0.1666 degrees, which with a leg length of 0.1 inches is 0.00048". A reasonable measuring system will be 4 times more accurate than this (or at least have 4x resolution) at 0.0001", toolmakers scope, cmm, x-y profile projector are all possible.