Checking a 45 degree square?

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DMIOM:
Rich,

Given you've already got an accurate 90 degree master square, I think you could make an assessment by adding just a flat base plate, 'something' with one known good straight edge, and a short length of known parallel bar - and no need for any scribing or interpretation thereof:

(i) Lightly clamp your straight edge to the plate. (ii) lay your new one against the straight edge (iii) lightly clamp the parallel against the upper edge of your new one, (iv) ease the new one out and re-lay it against the top side of the parallel, (v) compare this against your known good 90 degree master square.

Sketch below .....

Dave

loply:
DMIOM, I see how that would prove that the two 45s add up to 90, but you wouldn't know if you had a 44 and a 46 though? Or am I missing something?

I thought about using Pythagoras but I can't see a way to accurately measure the length of the thing, plus the slightest bit of damage to the edge of the triangle would make it hard to measure.

I'm trying to understand the method for using rings/bearings but I'm not getting it... Could someone explain? Do you mean to put two discs of different sizes side by side (like oO), having made the sizes of them such that an object laying over them would be at exactly 45 degrees? That seems like a plausible method?

Fergus OMore:

--- Quote from: awemawson on May 27, 2015, 05:38:09 AM ---Can one not precisely check or set angles by turning (and / or grinding) precisely sized disks and abutting them? Three such disks firmly in contact with each other can have straight edges tangentially touching two disks and forming an easily calculated precise angle between them?

--- End quote ---

As stated, you get 3 x 60degrees not 45. Mind you, I was wrong this AM :Doh:

You can ,Andrew, work a set of tool makers buttons but of different sizes- I think

Cheers

N

loply:
Just to clarify one other point, to be comparable with the accuracy I managed to get on my scraped parallel and master square ideally I'd want to get the 45 degree surface to be accurate to within about +-5 microns (ie 0.005mm) of where it should be, I mean the 'top' of it won't be any more than that from where it should be, if you see what I mean. I don't know what angular accuracy that translates to, but I'd probably make the thing about 6 inches tall...

loply:
I guess the attached image is what I was thinking.

By turning the two cylinders to size (and presumably finishing really carefully with some fine sandpaper) I could do the maths and end up with a parallel or suchlike lying across them at 45 degrees, I could then indicate off that to assess the one I was making/testing.

Kind of just like a sine bar really, but since I don't have a sine bar or a set of gauge blocks it saves having to buy them :clap:

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