How do I straighten Delrin?

How much is it bowed? Beyond just machining all four sides, did you ensure the part came from the center of the material? If you take . 030" from one side and .300" from the other, it will curl just like steel or aluminum.
Later,
Charlie
Reply to
Charlie Gary
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machine by equal amounts off each side.
Material = 1 1/2" dia x 15" long.
centre drill one end.
set up horizontal dividing head and centre on universal mill with table set to correct angle.
hold material with 12" protruding, centred end supported by centre obviously.
machine a nominal amount off one side, say to 1" from centre, roll DH through 180 deg and mill second side. Repeat step cuts until required sizes are met.
roll through 90 deg and do same with 1 1/4" sides.
machine off the unwanted centre.
Reply to
tpow
It's a thermoplastic, so it will soften before it melts (somewhere > 150 C). You might try laying them on a flat plate in an oven at 100 C, they might relax under their own weight, or you might need to go a bit warmer, or you might need to weight them down. They will go very floppy near the melting point and may move in other directions.
Reply to
newshound
I machined two tapered guide strips fron Delrin plastic. they taper
fron 3/4 inch down to 1/8 inch. the ends now bow up. I did machine
all four sides to get them to size first. How do I get rid of the
bow? heat?
1-1/4 wide tapered over 10 inches. 15" OAL.
Thank You,
Randy
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Reply to
Randy
Anneal the material either in air or oil.
This is grade dependent but DupIn Air: "The annealing of Delrin is best conducted in air-circulating ovens capable of maintaining a uniform temperature contollable within 5 degrees F plus or minus." "In air, one hour at 320F is required to reach the same degree of annealing as is achieved in 30 minutes in oil at 320F because the heat transfer takes place more sl;owly in air than in oil."
They also recomend that you cool the material slowly.
Recomended oils ( if you want to do it in oil) for the process include: Esso Primoil 355 Chevron White Oil N. 15 Plough NUJOL
This is all in the Dupont Delrin acetal resin design hanbook printed in 1967.
Reply to
John R. Carroll
Probably should have annealed before cutting, but you still can do it now. Anneal in oil if you can.
plastic material cut from rod has an awful lot of stress from the extrude process.
ca
Randy wrote:
Reply to
clay
Cheaper and easier to toss them and do it right. To each his own.
Reply to
John R. Carroll
Doesn't that rather depend on who is paying for the material and how he costs his own time?
Reply to
newshound
If I anneal it now will it straighten or bow in any direction it feels like?
It was a McMaster-Carr piece, looked like it was saw cut from plate.
sounds like I need to buy way oversize, anneal then cut.
Thank You, Randy
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Reply to
Randy
Just buy annealed material in the first place.
Reply to
John R. Carroll
Maybe I have missed something, but plastic raw stock I have yet to see sold as having any specific annealing.
Reply to
Richard J Kinch
"newshound" wrote in news:6h1ti3Fi4clrU1 @mid.individual.net:
Otherwise known as "sunk cost fallacy". So no, if you're a rational decision maker the amount spent so far should not be considered.
The money you've already spent is lost. You can calculate your cost to make the parts properly and if you are sure you can come up with a fool proof way to fix the parts then you can compare the two costs.
Right now fixing the part seems far from certain and has an unknown cost. It seems likely a repair attempt will just increase your loss. So a do- over is the best decision.
Reply to
D Murphy
From Carr perhaps but if you buy from a reputable plastics house that knows what they are doing they will either have it or aquire and resell it.
Like steels, or about any other material, plastics are almost always available annealesd. Especially sheet, tube or bar.
Reply to
John R. Carroll
I've always had a talent for this Dan and except for my language skills, this was my most valuable instinct as an officer back when I was a kid. Got called in on a Mattel project in the 90's, looked the tools over and the first words out of my mouth the next day with the brass were "We are throwing the tooling out and starting over". They nearly shit a brick but when all was said and done, they saw the wisdom and the shop that had built the original tooling was owned by one of their former VP's and his son so it was especially tense as we wnt forward.
You'd be surprised ( or maybe not ) at the stuff I've walked into and just thrown out and started over. Entire multi cavity molds in a machine, machine tool bases, automation equipment or machining fixtures - you name it.
It's amazing what California real estate appreciation and the home mortgage industry have produced when combined with a button pusher. I'm sure you have seen the phenomenon at first hand yourself.
Reply to
John R. Carroll
There is a book " Making great decisions in business and Life " by Henderson and Hooper that is worth getting out of the library and reading. It covers the sunk cost fallacy.
Dan
Reply to
dcaster
I can't find it either. Checked McMaster-Carr and found nothing.
Jon Banquer San Diego, CA
Reply to
jon_banquer
I'll keep checking, but my local plastics guy says annealed is kind of a myth. The extruders will add heat lamps where the material leaves the die to slow its cooling and they will mark that as annealed.
There is one other plastics supplier in town I'll call them.
Thank You, Randy
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Reply to
Randy
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.
Reply to
Richard J Kinch
I believe you are refering to the "measure twice cut once reality". LOL
Reply to
John R. Carroll
"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.
Reply to
D Murphy

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