Lathe Machining of Delrin

[mmcmdl]

Obviously the steady rest is out of line.

Agreed . Long shaft work is fun but takes some time and operations to setup correctly . I machined and ground large Worthington Pump shafts for years . Had to hand center drill one end , mount in lathe on that center , machine a spot on the shaft for a steady rest , mount and fit the steady rest to shaft while still in center , remove tailstock and re-tool center . The steady rest could then be removed when neccessary . After heat treating , many times after putting them between centers on the cylindrical grinder , I had to re-lap the centers to pull the warpage back in so the shafts would clean up . We always left .030 minimum on these large shafts for heat treating .

Once the shafts were good and the taper was pulled out of the grinder , these were gravy runs . Weeks and weeks of watching the grinder do it's job , until I got down to the shi* house or the Penthouse pass . I miss those days .

 

[Weldingrod1]

On the subject of turning plastics, a 6 jaw works a LOT better for "thin" wall stuff. For plastics a 1/4" is a thin wall
I've sucked lots of plastic parts out of the chuck... I usually forget to swap to the annoyingly heavy 6 jaw.

Sent from my SM-S911U using Tapatalk

 

[btvarner]

Wow! Amazing responses, great suggestions! I stepped away and watched the game last night. Took time to digest answers + I wanted to try the suggestions before responding. I have solved the problem.

Causes:
1) Pilot Error. Study Rest was not concentric with the chuck.
2) Too fast RPM
3) Chuck Jaws Too Slick

Details:
1) I rarely use the study rest & forgot/bypassed the setup process. The last time I used this rest, the diameter of the workpiece was (sort of) the same diameter. Delrin size was 2” x 12” round. I placed the material in the chuck, installed the study rest about 3” from the end, wrongly assuming the bottom two roller guides were concentric with the chuck. Touched the Delrin with the top guide & dial indicated from there. Of course, I got a good reading & believed everything was good to go. The whip (Which I could not see with the eye) helped cause the material to work its way out of the chuck.
2) RPM was at 1250.
3) Although I have never had any issues with ferrous material, the jaws are apparently too slick.

Solution:
1) Used correct setup procedure. With such a long piece of Delrin I used the bottom of the study rest to support the very end of the material, while I dial indicated the runout near the chuck. Adjusting the 2 bottom guides during measurement until the indicator near the chuck read true. Then carefully moved the study rest as close to the chuck as possible & readjusted the 3 roller guides to just touching the Delrin. Moved the study rest to about 3” from the end of the Delrin & secured.
2) Reduced RPM to under 500
3) Wrapped 150 grit sheet rock screen between jaws and Delrin.

Doing the above resulted in the stock staying in place while spinning (No live center). Using a live center along with the study rest during turning & facing operations functioned fine.

I still feel like this 3-jaw does not hold the Delrin well enough. I believe I will in the future make a split sleeve to place under the jaws.

Again thanks to everyone for their help!

 

[tobnpr]

I still feel like this 3-jaw does not hold the Delrin well enough.

I suspect the root of your issue is that your jaws are bell-mouthed...I would check them, or as you say- new chuck.

 

[RJSakowski]

It is not reasonable to expect a 12" bar of 2" diameter Delrin to remain securely clamped in a three jaw chuck with less than an inch of jaw grip. Delrin is compliant and would easily yield to adverse force.

 

[RJSakowski]

An obvious solution is to use a shorter piece of Delrin. I was faced with this situation as well. My solution to the waste of all the cutoffs was to use a sacrificial piece of Delrin and weld my short piece of stock to it with a soldering iron. When you finish your part, you just part it off and clean up the weld area, ready for the next part.

 

[Charles scozzari]

An obvious solution is to use a shorter piece of Delrin. I was faced with this situation as well. My solution to the waste of all the cutoffs was to use a sacrificial piece of Delrin and weld my short piece of stock to it with a soldering iron. When you finish your part, you just part it off and clean up the weld area, ready for the next part.

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

 

[Parlo]

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.

 

[D.sebens]

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.

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

 

[stobl]

Something isn't right.

I just made a few front caster bushings for my old zero turn. Started with a 12" long piece, and didnt have issues. However, i found a better process to crank them out faster, so i ended up cutting off the 1.5" chunks and holding them much closer to the chuck.

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.







and yes, ignore the complete mess in the background. In the middle of a complete reorganization of my little space and had to make these parts.