Machining rubber

[Voicecoil]

I need to make some parts from some reasonably hard (shore 80A) rubber, just wondering how possible it is to machine it? Anyone ever tried it? It would save a lot of time and money over moulding them.

[JAZZCNC]

A Long time ago I machined some 10mm thick rubber gaskets for a vacuum tanker and it went well enough but I think the thickness helped and it was reasonably hard stuff. Used a single flute cutter and cut in one pass.
If it's thin stuff I think I'd use a board on top to hold down and cut thru both at the same time.

[mekanik]

can you freeze it ?

[Voicecoil]

A Long time ago I machined some 10mm thick rubber gaskets for a vacuum tanker and it went well enough but I think the thickness helped and it was reasonably hard stuff. Used a single flute cutter and cut in one pass.
If it's thin stuff I think I'd use a board on top to hold down and cut thru both at the same time.

Thanks for the info, mine is about 20mm thick and so should be reasonably self-supporting I guess: quite a thickness for a single pass cut though!

[Voicecoil]

can you freeze it ?

That's a good suggestion, however I don't have a fridge in the workshop (it's quite cold enough as it is to not bother about food going off :cold: ), but I guess as long as I'm quick I could stick it in the freezer at home and give it a quick squirt of aerosol freezer when I get in.

[JAZZCNC]

Thanks for the info, mine is about 20mm thick and so should be reasonably self-supporting I guess: quite a thickness for a single pass cut though!

Ye don't think I'd be trying 20mm in a single pass but I seem to remember I was surprised how easy cut. I think it's a little like cutting soft aluminum where taking a big bite works better because it keeps the heat down.

[Robin Hewitt]

I thought rubber was usually ground so I just googled rubber grinding and there it was :fat:

[Voicecoil]

I thought rubber was usually ground so I just googled rubber grinding and there it was :fat:

That's an interesting idea and yes, it seems a lot of rubber parts (particularly softer ones) are ground. I've added a carbide burr onto my APT order, it'll be interesting to see how it goes.

[magicniner]

I cut some polyurethane at 30000rpm with new, razor sharp 3 flute HSS cutters and oil free flood coolant (I've done some with air too), around 1mm DOC per pass, the parts were 10mm wide 1.5mm wall tyres for a steel tape labelling machine, they came out really nicely.
There is no good, useful info out there on machining rubbers and polyurethanes, most of what has been offered is misleading or unhelpful, like "freezing" ;-)

[Voicecoil]

Thanks for the advice. BTW, what diameter cutters were you using please? - it would be useful to get an idea of a workable SFM.

[magicniner]

It was an 1/8" cutter, it was only a small job and I figured a smaller cutter would be less likely to deform the material as it cut, the waste comes off like dense fluff bit the cut surfaces are nice and smooth.
I have some more things I want to do in Polyurethane but I need to build a speed increaser on a BT30 for my new CNC mill first.