[Darth Yoda]

Hi guys. I'm turning some 2.5 inch delrin at 800 rpm and getting decent finishes with a coated carbide tool. I get an 8 minute run time with a .006 feed and am trying to reduce it if possible. I did a bit of googling and got different answers (surprise) so here I am.

According to Plastics International the speed should be "950-1950 ft/min".
NYTEF Plastics reports "450-600 sfpm" rough and "600-800 sfpm" finish.
Both number are under the turning sections so it's not a mill vs. turning comparison. I feel the gap is way to wide to be correct unless I'm missing something.

Assuming my math is correct, 2,5 X 3.14 =7.85 inches / 12 =.654 ft. So 800 rpm should be 523 ft/min which tells me to go higher in rpms. BUT if I go to PI suggested speeds it will go to 2217rpm.
The median speeds for PI is 1450. So 1450 divided by .654=2217 rpm.
NY has 800 divided by .654= 1223 rpm or half of PI's 2217 rpm.

Which should I go with short of a number of one=off runs as a trial or is that the best route to take?

What are your speeds and feeds?
Man!My head hurts...............

[Geof]

I run Delrin as fast as I run 6061 or sometimes faster so I would go for the higher speed, 2200rpm or even more, you could also boost your feed at least for roughing. I suggest you also try using the highly polished uncoated micrograin carbide inserts made for aluminum, they give an excellent finish on Delrin.

[Curlychip]

There are a variety of ways to reduce cycle time. One is surface speed, another is depth of cut and a third is feed rate. Altering one or all of these can shorten your cycle time. An uncoated positive insert (mentioned by Geof) is a good way to go. Is this with a manual lathe? Are you able to use coolant? Is 2.5 your finished diameter? On a side note....your math calculations almost made my head explode! Try SFM / d X 3.82 Works like champ and is easy to remember.

[Darth Yoda]

Thanks for the replies guys. The 2.5 dia is rough stock. The dia's vary with 2.14 being most common followed by 1.809 then other smaller parts.

These are being cut on a HwaCheon 31 cnc. Coolant can be used but so far isn't needed. I've already tweaked the program to optimize depth of cuts and such. It's actually a tube with holding ridges on the outside.
I'll remember and use your formula for sure!! Thanks!!