Checking a 45 degree square?

Gallery, Projects and General > How do I??

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Fergus OMore:
Both sine bar and Jo blocks are Imperial. Again, all my measuring tackle is Imperial.

Of course, I can work in Metric but my tools are also Imperial- apart from the Unimat clone. Just old fashioned, I guess.

Fergus OMore:

--- Quote from: loply on May 27, 2015, 09:34:45 AM ---This is what I mean:

--- End quote ---
If you make Two, you become parallel!

vtsteam:
Loply you don't need an indicator. An adjustable hard point will do. You just need contact both ways.

Besides, do you have an indicator that measures the 10 microns which is your goal?

The real question that has been missed all along, is not how to measure or get an angle, which you can do with many methods discussed and others as well, but how to rub and scrape it to that angle using contact methods, rather than measurement methods, which are the inevitable step in any mathematical determination of angle.

Sure, everyone knows Pythgoras theorem and owns a calculator, but once you've done the math how do you translate that without measuring? Sine bars and machined holes and pins are all measured somewhere along the production process -- whethere it is of the mill table calibration, mill tool size, mill movement, etc, and NONE of those are to my knowledge done to a 10 micron tolerance.

The whole essential of traditional hand scraping is a method which does not depend on measurement, but upon indicators of contact. We use math to do approximate work, and discard math in favor of contact and a contact indicator (blueing) to do extremely precise work.

I've already given a contact method which will, with a contact indictor, allow a person interested in a practical method, to scrape, and see non-contact areas. It will work as is.

I'm sure it could be improved upon (as most things can) with slight modifications to get work done more efficiently, though not necessarily more accurately. But most of what I'm reading here ignores the tolerance stated and the methods necessary to reach it. No system of measurement with a lower tolerance anywhere along the line of production will guarantee the tolerance required by the OP.

DMIOM:

--- Quote from: loply on May 27, 2015, 09:31:37 AM ---Dave - that's boggling my mind a bit! I'm still a bit unsure how I would know which way the error was, I'm sure it's possible I'm just getting confused :hammer:

Having said that - I think I've just come up with a way of doing it which only requires one 45 degree part and the master square-

If I set up an indicator on the master square such that it's tip is about 10mm off the surface of the square, pointing downwards, and bring the 45 degree and butt it up against the master square such that the indicator reads off it's height (say about 10mm 'in' to the 45), note the indicator reading, then turn the 45 around and do the same on the other side. If it's not 45 the reading will be different, if it is 45 the reading should be the same.

It would then just be a case of scraping off whatever the error was from the 'high' side, and re-flatening the thing.

--- End quote ---

Rich - your indicator method doesn't (IMHO) make use of the full length - you're trying to make an ultra accurate measurement over a short span.

Have made another sketch to show how you would tell if one corner was too fat or too acute (the examples have 43&47 degree angles to make the differences visible)

Dave

Fergus OMore:
Steve's interesting observation etc raises the question of just how thick this thing is going to be.

Can you clear this up and tell us what tooling you have already for establishing your claims of accuracy.

Cheers

Norman

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