Lathe Machining of Delrin

[RaisedByWolves]

I always thought if you ran in reverse it would put the material back on.

That only works if you sprinkle the chips over the tool bit.

 

[Parlo]

Also I was pleasantly suprised- the best cutting I had on it was with a parting tool (new chinese carbide insert) and heavy sideways cuts. It streamed off like ribbon in manageable sizes. Still a complete mess, but a lot easier. If I remember right, it was cutting at about a 7tpi rate while i was hogging it down to size.

It looks like you were turning Nylon or UHMW polyethylene. Delrin machines well using standard tooling and chips much more easily than Nylon type plastics.

 

[stobl]

Oops. Specifically It's UHMWPE since I use it a lot for boat related bushings

 

[Charles scozzari]

It looks like you were turning Nylon. Delrin machines well using standard tooling and chips much more easily than Nylon type plastics.

If you are aggressive with Nylon the cutter will bite and destroy the work.

 

[Parlo]

If you are aggressive with Nylon the cutter will bite and destroy the work.

I think this applies to all materials.

 

[RJSakowski]

I think the jaw length of a 8" chuck is an advantage holding Delrin, But I never had any difficulty using my Atlas 618s 5" 3 jaw chuck either

Nor haveI, even using a 3" chuck on the 6x18 but running with 11" or more of stickout is asking for trouble. It appears that the issue has been isolated to steady rest misalignment. The OP stated that the problem occurs before any machining is started.

An off center steady rest will result in a wobble on every revolution which will cause the stock to work its way out of the chuck. I haven't seen this phenomenon occur on solid rod but I have definitely seen it on PVC or ABS tubing. The wobble technique is also one that I use to get sticking shafts out of a hole.

If as suspected, the steady is misaligned and is pulling the part out. Run the lathe in reverse with an inverted tool & it should drive the rod towards the chuck.

That would only be true if the steady rest was twisted,causing the rollers to travel a helical path. If there is radial misalignment, the direction of rotation won't matter.

 

[Parlo]

That would only be true if the steady rest was twisted,causing the rollers to travel a helical path. If there is radial misalignment, the direction of rotation won't matter.

It also depends on whether the helical path is right or left handed. If it is pulling out in forward rotation then it would do the opposite in the other direction.
If it were radial misalignment, it would not be pulling out of the chuck. So it seems clear that the steady is twisted. This variable is often not considered as important as it should be & not generally checked.

 

[RJSakowski]

It also depends on whether the helical path is right or left handed. If it is pulling out in forward rotation then it would do the opposite in the other direction.
If it were radial misalignment, it would not be pulling out of the chuck. So it seems clear that the steady is twisted. This variable is often not considered as important as it should be & not generally checked.

On the contrary, the radial misalignment is what causes the pullout. As an example , if the misalignment is .05" towards the front, the rod will be twisted in the chuck towards the front which causes the end of the rod facing the touching the chuck face to lift slightly. As the spindle rotates, the end of the stock will be precessing, lifting a little more with each revolution until it eventually works its way out of the chuck jaws.

 

[Parlo]

On the contrary, the radial misalignment is what causes the pullout. As an example , if the misalignment is .05" towards the front, the rod will be twisted in the chuck towards the front which causes the end of the rod facing the touching the chuck face to lift slightly. As the spindle rotates, the end of the stock will be precessing, lifting a little more with each revolution until it eventually works its way out of the chuck jaws.

Yes, you are correct. I wrongly assumed the rod was correctly indicated true to the steady and lathe centreline so the only option left was that the steady was not square to the lathe centreline.