machining tolerances for plastics 2

[FredEvans]

I am looking for machining tolerances to be used when
specifying tolerances on machined plastic components
( teflon,delrin and nylon,poluurethane)

It would be appreciated if anyone could point me in the right direction

Best regards from south africa

fred evans

 

[unclesyd]

Tolerances depend on the machine operator and equipment setup. Tolerances are also dependant on the base material you are working with. There are some engineering plastics that you can get to less than 0.001" and other that will never see anything close to this.
Here two guides on that should get you started with machining plastics. I have always look at setups for Aluminum as a starting point for machining plastics. You need to get specific machining instructions for what ever material you are working with.

http://www.plasticsintl.com/documents/Guidelines for Machining Engineering Plastics.pdf

http://www.curbellplastics.com/technical-resources/pdf/plastics-machining-guidelines.pdf

 

[KENAT]

Well, first off, shouldn't you base your tolerances on function first?

Obviously though manufacturing capability does have to be taken into account.

unclesyds links are nice, I'd also look at talking to your likely vendors/machine shops and talking to the manufacturers of the specific plastics.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[unclesyd]

There a wealth of information on the Connecticut Plastics site. They will show you what can be accomplished.

The site is a little convoluted so look around

http://www.connecticutplastics.com/capabilities-and-parts/process/plastic-turning/