5 micron tolerance cutting nylex

hi guys

the boss gave me a drawing today and said make 40 of these the part was simple 18mm max diameter with 1 step and a few champers tapped m8 though. then i saw the tolerances +.005mm -0.000. i asked why the tolearance is so tight espesically with nylex (nylon) he said its a press fit. I said can i have a realistic tolerance...... well you know the answer i got. So set up and started making these parts and after a about 20 minutes i had a about 4 in tolerance and at least 12 out of tolerance not by much .001 .002 etc lots of varience for no reason. they ended giving the first 40 the ok so i guess the tolerance had changed?

Anyway i was wondering if it possible to pull this of and keep 100% within tolerance and if so how?

Thanks

ian3846 said:

...espesically with nylex (nylon) he said its a press fit...

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The solution is easy: measure the specimens with undersize IDs and oversize ODs when it is dry out, and the specimens with oversize IDs and undersize ODs when it's raining.

Plastics (At least Delrin) also have a nice tendency to "grow" overnight after being compressed in the collet chuck. Ask me how I know....

Rocketcheese said:

Plastics (At least Delrin) also have a nice tendency to "grow" overnight after being compressed in the collet chuck. Ask me how I know....

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grow.... by how much under what clamping preasure?

I´ve had parts grow over .01 mm overnight in Delrin.
I forgot to turn down the chuck pressure before I ran the parts, and used the same as for running metals.
If I remember correctly that was over 30 bars (450 psi) on the hydraulic gauge. (Don´t know how much actual pressure that represents in the collet on that machine - Index G65)
Not fun!
My boss checked them and throwed them in the bin...