Finish on soft plastics

[Dean jeffery]

2mm thick black nylon seems to be hard to find, unless from direct plastics.

Customers are happy with a shit finish I'm not, and wanted to improve the quality of product.

[m_c]

What we're trying to highlight, is that that finish is down to cutter/work piece deflection. The fact it's only noticeable in certain materials, doesn't make it a problem with the material.
If you zoom in on that last pic, the problem is still there, it's just not as obvious.

Different cutters and materials will create different cutting forces and resonances, so what can be barely noticeable with one material and cutter combination, can become glaringly obvious by just changing either the material or cutter. And if you have any flex/backlash in the system, any issue can get amplified.

[magicniner]

The material is so soft that it's what you're doing with it and not the material causing the problem, have you tried disposable HSS 2 flute endmills (Carbide isn't as sharp unless you grind it razor sharp yourself and then it's a crap-shoot on anything but plastic so you have to reserve the tools for plastics), with lots of air from several directions to shift the chips and adequately cool the tool and material in all cutting directions?
Another alternative is the above plus a shallower cut using a ramped profile path.
Something as simple as ambient temperature differences can change what happens when you're cutting temperature sensitive materials and your basic set up isn't adequately controlling all the required environmental variables.
This stuff quite literally is Rocket Science ;-)

- Nick