×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Machining Delrin to high Flatness and Parallelism

Machining Delrin to high Flatness and Parallelism

Machining Delrin to high Flatness and Parallelism

(OP)
Hello All

I need to machine a plastic piece that is rather thin with high flatness, parallelism and surface finish callouts. I was thinking of lightly thinning some stock high-maintainability Delrin. See the drawing below:

http://imgur.com/igV3fsB

The piece is 190mm X 100mm. Now these tolerances may be unreasonable, but what could be realistically be hit by a CNC milling machine without getting too expensive or complex? Is there a plastic material more suitable to this application than Delrin?

Thanks!
Justin

RE: Machining Delrin to high Flatness and Parallelism

"high-maintainability Delrin" ? Never heard of it.

Ordinary Delrin can be machined as flat as you specify.

Don't expect to measure it half an hour later and get the same numbers.

If you assemble the part between two other parts, and e.g. rely on the flatness for sealing, do the assembly immediately after finishing.

Remember that Delrin is a condensation polymer, and has a thin layer of 'foam' in the middle of its cast form. You probably need to try shaving both sides of 1/4" cast material, or bandsawing the outer faces off 1" cast material.
I don't know which will warp more.

Mike Halloran
Pembroke Pines, FL, USA

RE: Machining Delrin to high Flatness and Parallelism

(OP)
Thanks Mike. Yeah I'm just talking about Delrin Acetal Resin. I assume the tolerance changes will occur due to the part cooling? Do you have any idea by how much the variation could be? The part will not be used in a sealing application, but as a spacer in an automated machine that will need to draw vacuum through it, thus the need for high flatness and parallelism. I don't want to use a metallic material as I need the part to be plastic for inductive sensing purposes.

I believe 3/8" sheet stock will be purchased and then about 2.86mm will have to be removed total, from either side.

RE: Machining Delrin to high Flatness and Parallelism

How about achieving the same effect by getting some metal sheet and then adhering some plastic tape on either side? Contact C S Hyde for PTFE or any other type of tape. Will be way easier to get the right thickness and tolerances and way cheaper too.

Dr. Chris DeArmitt

Plastics consultant to the Fortune 500: www.phantomplastics.com

Webinars on plastics, fillers & impact modification: www.plastictraining.com

RE: Machining Delrin to high Flatness and Parallelism

We have fairly good luck in getting 3/8" - 1/2" PTFE double-disk ground to a precision (+/-.001") flatness/parallelism, but we specify same with the material restrained between metal plates (as that's how it gets used). Oh, and surface finish is probably closer to 32 micro-inch rms, not 16.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources