How do I straighten Delrin?

Not to be confused with the "sunk cost fallacy fallacy", where you avoid choices that would lead to sunk costs, because you have a hard time not committing the sunk cost fallacy. I can't as much as cut a rough workpiece off a bar of raw stock without feeling it.

I believe you are refering to the "measure twice cut once reality". LOL

On Tue, 19 Aug 2008 15:01:29 -0500, Randy penned the following well considered thoughts to the readers of rec.crafts.metalworking:

I don't know where you are .... you could use some 1:1 help. Some of the responses yo have received are nuts. Email, if interested....

"John R. Carroll" wrote in news:cO2rk.20346$ snipped-for-privacy@flpi144.ffdc.sbc.com:

I've seen people just keep plowing ahead with a tool that doesn't work or a fixture that is junk. They act like the machine tool is a slot machine. Maybe this time when I push the button it will work.

Yup.

Randy wrote in news: snipped-for-privacy@4ax.com:

It could also be that your machining process put the stress into the material. Dull tools, improper geometry, and too much heat (speeds too high) can all cause stress to build in the work.

I was using a just resharpened end mill. I need to find the SFM for delrin I was 524 SFM. 1000 rpm. Workpeice did not get warm.

Most likely I need to slow it down a bit. Got new materail that the supplier annealed for me, started way over size I now have 2 blocks to size and straight. 2 hours of skim cuts and flipping them over.

Thank You, Randy

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Randy wrote in news: snipped-for-privacy@4ax.com:

I show face milling with a carbide inserted cutter recommended at 650 SFM for a 0.040" DOC, 600 SFM for a 0.150" DOC and 550 SFM for a 0.300" DOC. Feed around 0.005"-0.009" per tooth.

So if you are using carbide you're probably in the ball park. For HSS you'd want to 300-400 SFM with roughly the same feed rates.

I'm using HSS, my carbide face mills do not have a real sharp cutting edge. Thank You, Randy

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Randy wrote in news: snipped-for-privacy@4ax.com:

Randy,

This is probably one of those cases where taking light cuts at light feed rates will make matters worse. Delrin has low thermal conductivity and a high coefficient of expansion. The chip won't carry much of the heat away from the work. I would run closer to 300 SFM take a decent DOC if the set up is rigid and feed closer to 0.010" IPT than 0.005". Use a cold gun if you have one or coolant of it's allowed.

Dan, Thanks for all your help. I actually did this on my manual mill so feed per tooth is an unknown. Second set of bars turned out really good. Cutting the taper I started with 2 cuts at .150 DOC then finished at .075 DOC. No cold gun but I did use an air nozzle to cool it a bit and keep chips clear.

Thank You, Randy

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Randy wrote in news: snipped-for-privacy@4ax.com:

I'm glad it worked out for you.