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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Annealing Delrin Guides

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rgb1:
Annealing and stress relieving are two distinctly different processes, though
people in the plastics industry will oftentimes use them interchangeably.
Most delrin, but not all, will already be stress relieved by the manufacturer......
your supplier should have such information.
To ensure good dimensional stability on low tolerance parts, I use the boiling
water method (5-10 minutes depending on thickness) prior to any machining.


                                                                                         Ron

Artie:
Thank you for the clarification Ron. It's all very interesting to me. One issue is perhaps genericized trademarks, Delrin for example. Homopolymer vs coplymer, selling acetal under the Delrin tradename when it's actually unbranded copolymer acetal, distinctions I was blissfully ignorant of until yesterday. I highly doubt it makes any difference for spring guides but it does complicate Google searches.
So now I know of two people that boil Delrin or acetal. One boils after machining, the other before machining. You comments are knowledge based, the other guy's comment was empircally optimistic, "I don't know why it works but it does." The assumption is he had a problem with broken guides before the boil. I'm gonna try it your way.
Next question, do you use your wife's sauce pan or her pressure cooker?

Vee3:
FWIW, in machining 1000s of acetal parts of all shapes and sizes, I found that the white (natural) stuff was always more brittle than the black. I have no idea why.

Artie:

--- Quote from: Vee3 on February 15, 2019, 11:44:47 PM ---FWIW, in machining 1000s of acetal parts of all shapes and sizes, I found that the white (natural) stuff was always more brittle than the black. I have no idea why.

--- End quote ---

Go figure. I placed an order yesterday.. white

nced:

--- Quote from: Vee3 on February 15, 2019, 11:44:47 PM ---FWIW, in machining 1000s of acetal parts of all shapes and sizes, I found that the white (natural) stuff was always more brittle than the black. I have no idea why.

--- End quote ---
Hummmmm.....according to McMaster Carr it seems that both black and white have the same specs regardless of the color..........


Delrin vs Acetal...........
https://www.iplasticsupply.com/plastic-materials-list/acetal-delrin-celcon-basf-pom-pomalux-sheet-rod/

According to this "applications box" of the above link, there are times that Delrin is actually stress relieved before the final finish cut..........
"This materials is an excellent machining material – a favorite of machinists. Works like a soft brass, and has exceptional dimensional stability. It comes as a stress relieved material, however if you plan to do extensive machining, you may need to stress relieve the parts prior to final pass. Rods are machined well in lathe and mill, sheets are machined or cut in most common machine tools."

Doing some comparisons on the McMaster Carr site and found some interesting stuff.........

Price:
Delrin....1 1/4" diameter......$7.00/ft
Acetal....1 1/4" diameter......$7.62/ft

Tensile Strength:
Delrin....9,000 psi (Good)
Acetal....6,400 psi (good)

Anywhoo, I really never paid much attention to "black vs white" or even "inherent center-line porosity in the Delrin Homo-polymer version" simply because about 10mm of the rod center is drilled out for clearance with the piston latch rod.

A while back I bought some Acetal Homopolymer called (Rod, Acetal, 150, Wht, 1-1/8" Dia x 1 ft. L" (labeled 2XMH2) for $6.90/ft.
This site which claims a tensile strengtht of 11,000psi..........
https://www.grainger.com/product/DELRIN-Rod-2XMH2
The "(Rod, Acetal, 150, Wht, 1-1/8" Dia x 1 ft. L" (labeled 2XMH2)" worked just fine, however so did all the other materials I used.

Here is a pic of my rods.........

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