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S&S_ShovelHead
03-03-2011, 12:09 AM
I need to make two bushings out of UHMW plastic. I have a 10" X 4.1" peice of UHMW. The peices are to be 4" long, 0.25" is to be 4" OD, 3.75" is to be 3" OD with a bore of 1.9" running through the center. Im using a 10 X 22 lathe, The peice wont fit in my 3 or 4 jaw chuck when using normal jaws, when reversing them It will fit but I can only grip about 1/4" of peice and I can get it to turn strait. Also my steady rest wont fit such a big peice. Any tips of turning & parting these? I have little experience so Im at a loss. Thanks a ton.

Black_Moons
03-03-2011, 12:19 AM
You can use the center in the tailstock to help align it while holding it in the jaws... However UHMW is a nasty plastic, its soft, flows away, slippery.. I don't think you'll be able to really turn it iwth only 1/4" grip. Iv had chunks rip 1" of griped UHMW out of the chuck when I tryed to turn it a few inchs away from the chuck and took a reasonable cut. Left big jaw marks in it too.

madman
03-03-2011, 12:44 AM
Well saw out some soft jaws for youre work holding dilemna. Then weld add weld and so on chuck it up machine it true mount youre part(Harley??) and machine away. Good luck Mike

Westline
03-03-2011, 12:54 AM
I have used this before when I machined big pieces of nylotron.
Get any steel pipe that will fit over the piece ....bore it to have it run true.
Then just cut a slit in one side and use it over the piece in the chuck like a collet. It greatly improves your grip and no jaw marks.

RussZHC
03-03-2011, 01:46 AM
Bore it first (workpiece held stationary on the carriage), then hold it from the inside?
Or bore it first, inserts mandrel, use mandrel to turn to size, then hold it from inside (or leave it on mandrel to part...sacrificing a small fraction of the mandrel surface when you go through the UHMW) ?

S&S_ShovelHead
03-03-2011, 10:28 AM
Bore it first (workpiece held stationary on the carriage), then hold it from the inside?
Or bore it first, inserts mandrel, use mandrel to turn to size, then hold it from inside (or leave it on mandrel to part...sacrificing a small fraction of the mandrel surface when you go through the UHMW) ?

This sounds like my best bet, how do I accurately bore it though? My spindle bore is 1" so would you recommend I bore it to 1" for mandrel then turn to size then finish bore to correct size?

Rosco-P
03-03-2011, 12:12 PM
Turn the OD to size, held in 4 jaw, live center in the tailstock. Part off to length. Bore out on the mill. Sweep the OD to get the part centered for boring.

Carld
03-03-2011, 12:40 PM
Your dimensions don't look right.

Quote: "The peices are to be 4" long, 0.25" is to be 4" OD, 3.75" is to be 3" OD with a bore of 1.9" running through the center."

You say the part is 4" long but what do you mean when you said, "0.25" is to be 4" OD"?

Then you say, "3.75" is to be 3" OD?

I will assume the bore is really to be 1.9" and you will be parting the 10" long piece into the 4" long parts.

How many 4" pieces do you need? Two? That's all your going to get.

If the ends are not square to the length you need to saw them square as possible. Most reversed chuck jaws have a 1/2" step and that should hold the piece.

If so, cut the piece into two 5" long pieces use a block of wood against the end with the tailstock and live center holding it against the chuck. Turn the OD to what ever dimension you want. Face the end then drill a hole and then use a boring bar to finish to size. Use a very sharp HSS to cut the UHMW, it's sensitive to dull tools and will get push off and not cut to size.

Saw the excess off and then chuck up and face the saw cut.

Peter.
03-03-2011, 12:56 PM
If your machine is so small it can't hold that 4" piece in jaws the conventional way is it going to be good enough to hold the 1.9" bore over 4" length? I doubt such a small grip would hold it for boring.

What about clamping it down on the saddle and boring between centers first, then machining the OD features?

S&S_ShovelHead
03-03-2011, 01:20 PM
Your dimensions don't look right.

Quote: "The peices are to be 4" long, 0.25" is to be 4" OD, 3.75" is to be 3" OD with a bore of 1.9" running through the center."

You say the part is 4" long but what do you mean when you said, "0.25" is to be 4" OD"?

Then you say, "3.75" is to be 3" OD?

I will assume the bore is really to be 1.9" and you will be parting the 10" long piece into the 4" long parts.

How many 4" pieces do you need? Two? That's all your going to get.

If the ends are not square to the length you need to saw them square as possible. Most reversed chuck jaws have a 1/2" step and that should hold the piece.

If so, cut the piece into two 5" long pieces use a block of wood against the end with the tailstock and live center holding it against the chuck. Turn the OD to what ever dimension you want. Face the end then drill a hole and then use a boring bar to finish to size. Use a very sharp HSS to cut the UHMW, it's sensitive to dull tools and will get push off and not cut to size.

Saw the excess off and then chuck up and face the saw cut.

0.25" length is 4" O.D. 3.75" Length is 3" O.D.

I need two peices.

RussZHC
03-03-2011, 06:01 PM
From my view I am not certain the size of the bore for mandrel makes much of a difference...go with what works best/easiest to make for you. Confess I was thinking 1.9" right away but your way makes way more sense.

I made the suggestion because, to me, the way to gain support/grip given info you gave was to bore a hole, whether to finished size immediately or not, so to gain another option of workholding/surface.