Using Metalworking Tools on Plastic

"Paul Hovnanian P.E." fired this volley in news:WOydnV3Q8MyHBF_TnZ2dnUVZ snipped-for-privacy@posted.isomediainc:

and often a zero or slightly negative rake to prevent hogging and self- feeding.

Lloyd

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In that case, I would look into using a table saw. For cuts that shallow, heating should not be a problem. Accuracy should be enough. WAY faster than any metalworking approach.

Bob

I'm not a machinist by any measure, but I found that on a tiny lathe with UMHW, just using the back of a 1/4" HSS cutter blank slighly sharpened to the 15 degree angle they come at worked the best for what I was doing. This left left a perfect finish on the plastic and the chip or whatever.

sharp pointed cutting surfaces left grooves and tended to pull the material into the cutter. I made some tools that were curved, like a spoon and they still didn't work at nice as the end of a blank. I was just turning some rods down in diameter and facing off the ends.

Certainly not enough to justify using Teflon.

That -- or bend the contacts so they bow up in the middle of their length.

O.K. Very different from what I was interpreting your text as saying. Be sure to view this with a fixed pitch font (like Courier) to keep the drawing from being distorted

/ / / / / / // / / / ///   +---------------+ / ///   |               |/ ///    |             | ///    |             | ///    |             |///   |               |/   +---------------+

As I was drawing it, the (now added) diagonal lines would go along the 4.5" length, the 3/4" width would be the horizontal dimension, and the 1/4" would be the vertical dimension -- giving only room for a single strip on each side.

Obviously not what you intended to say.

You may want to make something too thick and finish with the mill (or a metalworking shaper if you had one).

A Woodruff key cutter is normally used to make a cut in the side of a shaft which is like a ')' in profile, into which a Woodruff key (like a slice off the edge of a coin) is placed, and part of it projects above the shaft to engage a groove in the pulley or gear on the shaft to prevent them slipping around the shaft.

However -- the cutter is *not* right for cutting the grooves in the direction you want. It does not have a long enough shank to reach along your shaft in the 4-1/2" dimension. I was assuming that the groove was parallel to the 4-1/2" dimension, in which case a Woodruff key cutter could do a nice job on either side of a piece of plastic clamped down to the table -- *not* in a vise.

Too good for your task, unless you need the low friction features of it. You aren't working with high frequencies, and certainly not with high voltages (2 kV to maybe 60 kV. :-)

Nylon should be fine for what you are doing.

Good Luck, DoN.

How about using pieces of 'phosphor bronze finger stock' or 'pogo pins'?

Well, if the contacts were to be secured by only one end, then I'd just let them bounce like a diving board, resulting in less metal fatigue. But, the wiping action I'm incorporating must allow for both directions across the contacts, which is why both ends of each contact has to be secured.

The *structure* the contact blocks will be permanently attached to will be wood, which must come together tightly and locked into place. Something like rubber will account for any expansion/contraction of the structure under conditions of varying humidity.

Ok. The 3-D image makes things clearer.

I'm not averse to hand tools. :-) (Which is preferable considering my present living environment). :-)

Ok. But I'll keep those in mind when I have to make a keyway in something like a motor shaft.

Yes. And Delrin has always been good enough for those low friction needs or for when dimensional stability is needed.

Thanks a lot.

Darren Harris Staten Island, New York.