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Angle Plates - How are they made?

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sparky961:
When performing the final grinding operation on an angle plate, how does one ensure squareness to a crazy degree of accuracy? What about without another angle plate to use as a fixture?

Lew_Merrick_PE:
Sparky -- I am assuming that this question involves a surface grinder.  Am I correct in this?

If so, there are a lot of variables surrounding the clamping of the angle that are dependent on other things, but the basis would be to use something like unto jack screws to support the to-be-ground surface and making adjustments until your "base" is true to the table using a knife-edge or die-maker's square before (& after) clamping.

Such angle plates are usually made in pairs such that you can blue-check the fit between them and scrape in the final form.

vtsteam:
I'm wondering if the fixturing method used for non-crazy accuracy with two raw angle plate castings, using a lathe, might just work for crazy, as well?

Here's how:

On the lathe for non-crazy, you take one as-cast raw angle plate, flatten (not square) the faces with a file enough to mount it so it won't rock on the faceplate. It doesn't have to be square yet, just flat.

Then bolt it on to the faceplate with a shim under it until the extending face IS square to the faceplate, checking with a true square.

Then you take your second raw angle iron casting, flatten the faces as before, and mount it to the first angle iron leg, which you made square to the faceplate. It now has a raw face that is somewhat parallel with the faceplate, and you proceed to turn that off flat, which makes it truly parallel to the faceplate and square to the other leg of its angle plate.

Then you take apart the rig, and mount the newly squared angle plate to the faceplate, and mount the second (still untrued) faceplate to it, and face it's extended leg true. Now both angle plates are square (non-crazy).

A similar process may be possible fo you using a flat but not absolutely true angle plate (or even angle iron) with shim -- checked with your true square, to yield a vertical surface to your surface plate for mounting your second and important piece to be squared.

chipenter:
Harold Hall used cylindrical squares http://www.homews.co.uk/page309a.html in his artical on angle plate from castings .

sparky961:
Thanks for the tips.  I was, indeed, asking about doing this on a surface grinder.  I believe that's the only way you could get close to the finish you see on commercial examples, not to mention the only practical way if the plate is hardened.

It seems the general consensus is that you need something square to begin with.  Be it a machine, a square setup by shims or other adjustment, or a proven master.  I thought there might be some "magic" method that zeros out any errors that may creep in.  I was trying to think of a way to use two of them in a way that would do this with theoretical perfection; kind of like when you lap 3 plates together in turn and end up with a dead-flat surface.  Unfortunately everything I could come up with so far just kept the two equal, rather than exactly 90 degrees.

I like the idea of using cylindrical squares for the reference.  I'll have to also look into how to accurately make one (or two) or those now.  I'm thinking if you didn't do it quite right you'd be relying on the perpendicularity of the lathe.  Taper is easy enough to eliminate but how to ensure the end face isn't concave/convex?  I suppose if you hollow out the bottom a bit it would only be sitting on a small circular ring of contact area.  Whether or not that face was dead flat would matter little at that point.

So, I'm left believing for now that you can only make an angle plate as perpendicular as you can make (and more importantly "measure") your setup.

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