As title, is t possible to machine polyurethan suspension bushes? The type I have are the hard black ones that Luego and GTS and probably other manufacturer use. I need to increase the inside diameter by about 0.5mm, but my efforts so far have just ripped up the surface of the material when I put a boring bar through on the lathe.

Before it's suggested I can't machine down what would normaly be the crush tube. This is for a non-locost application and the material that will be running in the bush is too long to fit into my lathe.

have you tried heating the tube and inserting it they melt easily with a welder so if you can ensure that the core does not wander this is probably as easy as it gets

You can machine the bushes much easier if the bar is frozen first. Just stick it in the freezer over night.

If its ripping sounds like it being turned at the wrong speed?

Ive machined PTFE bar and it was quite nice to machine once i got the speed right.
Oh also when i tried taking quite big cuts it didnt like that either!

Hi Mike

I bought a set of bushes from Lolocost and they varied in the length of the shoulder.

I turned them down so they were all the same and found I needed a tool with quite an angle on it.
A conventional tool meets the workpiece almost square. Did the id's as well. Used a 9/16th drill for
this as, due to the spiral flutes of a drill, the cutting edge meets the work again at an angle.

I hope you follow what I mean.

Paul G

Yeah it will machine ok.

Long while since i have ground any tools to turn plastics though so completely forgotten what the angles should be. I do know however you need plenty of top and side rake, and plenty of primary face and end face clearance. Basically making the cutting tip a sharp point and the edges like a knife edge.

Dont turn it too fast otherwise it will rip. Turn the speed and feed down. Not too slow on the feed though.

Bit of a guide here:

http://www.superflex.co.uk/superflex_universal_round_bar_machining_techniques.html

Hope thats of some help.

That's a good guide, basically freeze it and run your lathe as bloody fast as it will go!!

2000rpm on 1" bar is fast!

Thanks chaps, will have another go tommorow, remaining bushes in the freezer!

quote:

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Originally posted by NS Dev
That's a good guide, basically freeze it and run your lathe as bloody fast as it will go!!

2000rpm on 1" bar is fast!

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Well mine's a little ahead of that but still way off! Mine'll do 1200! (the little 3hp single phase motor struggles to spin the machine up at all in that gear!!)

Hmm, still not had a lot of success. Bushes do not need to be resiliant so will get some nylon to machine I think.

we always used to use Acetal bar for bushes on the rally car, didn't swell when wet like nylon can.

If you have no luck, try using Nylotron. It machines very easily and in not expensive. You can buy it from Engineering and Design Plastics in Cherry Hinton near Cambridge. I think they might send it to you but you would need to check that. They are very helpful and have a wealth of technical knowledge.

John

Phone number for Engineering and Design Plastics is 01223n 249431 HTH