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 .

Later,

Charlie

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.

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.

Anneal the material either In 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

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:

Too late for that now what he needs is straighten in a jig and hold it there while annealing...

Cheaper and easier to toss them and do it right. To each his own.

Doesn't that rather depend on who is paying for the material and how he costs his own time?

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

Remove 333 from email address to reply.

Just buy annealed material in the first place.

Nope sorry.

Maybe I have missed something, but plastic raw stock I have yet to see sold as having any specific annealing.

"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.

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.

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 s*it 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.

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

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

Remove 333 from email address to reply.

Known as in line annealed. Maybe everybody uses the process these days but your finished part says that isn't the case. They didn't used to, I can tell you that and as energy costs continue to climb extruders and molders will push the limits on these sorts of post processes. Acetal resins are extruded at about 360 degrees and properly supported out of the extruder while being allowed to cool evenly is as good a heat cycle as there is. Those heat lamps aren't what you'd see at your local Home Depot.

I haven't looked at Delrin lately ( about ten years) but the Acrylic tube I buy for a part has been annealed and it isn't sold that way. The certs., however, have the heat cycle in them and the specs. for the grade I use require it during processing.

No, it isn't, the sunk cost doesn't come into it. If you are retired and don't have much cash, but your time is free then it is worth spending any amount of time trying to recover it. If you put a small value on your time then, as you say, you also have to estimate the chance that you can't fix it. You have to compare the cost of *new* material (not the time/material already spent) with the time which you might waste on an unsuccessful recovery.

Well I agree with you. You should not consider the costs so far. However in this case if you can not get annealed material, you are going to have the same expense to anneal the new material as you will have to anneal the old material. I would try annealing the parts already made. The original message did not mention how true the parts have to be. So we are all guessing without enough information. If they have to be super straight, then starting over with annealed material is likely the right choice. But there is a lot to be said for knowing the tolerances and proceeding accordingly.

Dan