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Paul Alciatore
06-03-2010, 03:31 AM
I am making a special clamp to help me grind some spacers. I don't really need an exact size, but want the two ends parallel. The spacers are 1" diameter and have a 9/16" center hole. They range in length from 1/8" to 1".

I want an internal clamp in the bore and it needs to be less than 1/8" high to keep it clear of the wheel. My design is two pieces that have a taper between them. The outer ring is split to expand and grip when the inner piece is tightened down to the table with a 10-32 CS screw. I will make the inner ring from steel, probably whatever is in my scrap bin. I do not plan to harden it.

But I am wondering what would be best for the outer, expanding ring, steel or perhaps brass? Or what? The two rings must slide against each other so different metals seem a good idea. But what would grip the bore of the spacer better?

winchman
06-03-2010, 09:24 AM
Why not do it the easy way? Chuck up a round bar, turn the OD, drill/turn the ID, and part off the spacers. The faces will be parallel, and all the pieces will have the same ID and OD.

Ian B
06-03-2010, 10:35 AM
Paul,

If you want different materials, make the inner ring from bronze, and the outer split ring from steel. I'd think, though, that there'll be so little relative movement that plain old steel on steel would last long enough, especially with a dab of moly grease on the mating faces.

You mention grinding - I'll therefore presume the spacers will be steel. Why not hold them with a magnetic chuck? If the internal clamp is just there to stop the spacer getting spat off the end of the table, then a simple round pin would do the trick (or am I missing something?).

Ian

Paul Alciatore
06-04-2010, 02:43 AM
I am basically turning, drilling, and parting off now, but I am trying to get a better surface finish than I can get in the lathe. Perhaps it is overkill, but I am trying.

Bronze for the inner? Hmmm? Well, I planned on steel for strength there as it will take the force directly from the screw. Besides, I have already made it now. The outer ring would have to grip against the steel of the spacers. I'm not so much worried about the friction at the junction of the two rings, as you say a little moly should surfice. But the question in my mind really is would dis-similar metals provide a better grip than steel on steel.

As for the magnetic table, yea, I wish. Sorry, I don't have one. I'm doing a bit of cobbling here and going for tenths or better. It may work and it may not.

doctor demo
06-04-2010, 03:19 AM
Paul, is there any reason that the i.d. of the spacer can't be threaded?
Then just screw it on an apropriate length stud.

Steve

strokersix
06-04-2010, 09:23 AM
Would a split mandrel help you? Use an NPT plug in the middle to spread the split.

wierdscience
06-04-2010, 10:00 AM
What about two different hardnesses of the same material?

Paul Alciatore
06-04-2010, 11:41 AM
Paul, is there any reason that the i.d. of the spacer can't be threaded?
Then just screw it on an apropriate length stud.

Steve

Interesting thought. No, no reason at all.

Paul Alciatore
06-04-2010, 11:49 AM
Would a split mandrel help you? Use an NPT plug in the middle to spread the split.

Well, the smallest spacer is 1/8" so I am looking for a clamp that is less than that in height. I considered both internal and external clamping but thought internal would be simpler. Basically I need a clamp that is 9/16" in diameter and only about 1/10" high above the table.

Paul Alciatore
06-04-2010, 11:52 AM
What about two different hardnesses of the same material?

So I should just use a different alloy of steel? I can do that!