Finish on soft plastics

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.

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

These are the cutters I buy for cutting plastics, not tried or even thought about HSS tbh.


http://www.cutwel.co.uk/routing/rout...-63-850-series

Limited to 1 nozzle for air blast but can get another from work, will try that next time.

Cheers for the help and suggestions [emoji106]

If the surface defect is imperceptible to the touch have you considered flame polishing?
I use a waft of the old blowtorch flame on clear acrylic surfaces to improve finish and render machining marks almost invisible.

Not that I have had experience with nylon but I did read somewhere that some people but the nylon in a fridge or freezer to cool it then machine it. Just saying:whistle:

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Originally Posted by Clive S

Not that I have had experience with nylon but I did read somewhere that some people but the nylon in a fridge or freezer to cool it then machine it. Just saying:whistle:

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The colder it is the better it machines as it's harder when cold and chips shear off and clear the work better, if you have the extraction to safely do it alcohol mist with good air flow can be a boon for keeping heat sensitive materials cool

I bought a buffer to polish clear and solid coloured acrylics when needed, can't use the buffer on nylon though I tried [emoji23]

Yeah I've red that cool the plastic before cutting it

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Originally Posted by Clive S

Not that I have had experience with nylon but I did read somewhere that some people but the nylon in a fridge or freezer to cool it then machine it. Just saying:whistle:

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That's a very good idea. The only issue is that it will shrink in the freezer and expand when it is at room temperature, so if accuracy is important at room temperature then that must be taken into consideration.

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Originally Posted by Dean jeffery

The photos do make things look worse than appear, the cut lines can't be felt with the nail when run on the edge.

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I see shadows along those lines and that means the surface is not even. If it can be felt with your nails or not is another thing and depends on your own personal finger sensitivity.

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Originally Posted by Dean jeffery

More parts per sheet, some small parts are made from that same sheet, less tools to stock, less tool changers.

But I could get away with a 3mm cutter on that part without an extra tool change, I've done a finish pass on some 10mm acrylic with the same 2mm cutter to give a clean cut in the past.

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Yes, more parts but also greater risk for tool deflection if you are using 2mm cutters.

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Originally Posted by Dean jeffery

Only really any good doing full clean up passes on new cutters or soft material other wise you still get cut lines.

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But we are discussing soft material here... aren't we?

Also, the full pass cleaning I normally make is just shaving off about 0.1mm. That gives very good results, even if the cutter is not brand new.