Molded Tolerances

[sluggo]

Greetings;

(Part 1)
I'm looking for an RMA equivalent for plastic molded components indicating what tolerances are reasonable for given dimensions and geometries. I know the Society of Plastics Industry, Inc publishes something by material. Does anything else exist?

(Part 2)
Specifically, I'm molding a round piston stop that has an o-ring groove roughly 1.800" diameter. We're seeing roughly .015" variation (1.805 to 1.820)(out of roundness) with a .200" wall. Should I be expecting to do much better. The material is a glass filled 6/6 Nylon.

Thanks and God bless
Mike

 

[insideman]

Part 2:

Is the part symmetrically gated? I suspect a non-symmetric flow may be causing your problem.

Pat

http://www.aquasite.com/skonkworks

 

[miner00]

You also might want to look at the operating conditions. Nylon 6/6 has relatively high water absorption and as a result, dimensions can change quite a bit due to temperature and humidity. Nylon 6/10 seems to perform a little better. This might not apply since your part is not expanding uniformly, but I usually find it prudent to explore all of the options.

 

I've invented a kitchen garlic tool to be made of transparent thermo plastics such as ABS, polycarbonate, or acrylic. My main concern is that the material needs to be dish washer safe, quite durable and will not suddenly break apart creating a hazard if swallowed.

Since I'm not a plastics expert I'd appreciate any advice on the suitable material to use. Thank you.