Noob strikes again..this time its a plastic question

[Rickyg]

Looking for advice on machining thin home depot lexan sheets.
I have tried a couple different bits and speeds but no luck. I suspect I am using the wrong type of bit and wondering what is the right one.

What happens is I get a plastic build up on the bit..sort of a ball forms on the bit and then as the bit enters the plastic this ball beats up the plastic edge..well you can imagine the mess I get.

Let me know if anyone can.

cheers

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[awerby]

Lexan (polycarbonate sheet) actually machines pretty well, at least compared to most plastic. It doesn't melt onto the bit the way acrylic, for instance, does. Are you sure it's Lexan and not Lucite? How thick is the material you're trying to cut? Thin material is hard to hold onto; how are you mounting it to the bed? How deep are you cutting per pass? What sort of bit are you using, and how fast are the RPMs and feedrates you've tried? If you cut too slowly, it can cause the sort of problems you've noticed, as the bit will rub more than it cuts.

[Rickyg]

Hmmm you could be right it may be Lucite. I will need to chack next time I am at HD.
the material is about 1/8 inch thick and I am tryign the full 1/8 in the cut. It's held down wiht double sided tape.
Feedrate is about 600mm sorry I can't say aobut the RPM as its a router and not a spindle.
I have tried a chipper bit, a regular router bit..sorry not sure what they are called.
And a 1/8 ombsbrud type bit...no go.
Hope this helps.
I know its me and technique...just need the right direction

[ger21]

If you are using a router, then your rpm is probably about 25,000, which is way too high.

You want to use a single flute tool, like this:
https://www.ebay.com/itm/1-8-1250-si...wAAOSw-olaNZQj

And I'd increase the feedrate to 1500-2000mm/min.

[Rickyg]

aw I wondered if this was the issue.
Slow the router down as much as I can. Up the feed rate as much as I can. Basically don't spend to much time in one place melting the plastic...is this what I should take away.

cheers

[ger21]

Yes, but you also really need a single flute plastic cutting bit.

[Rickyg]

Ok. Order placed. Thank you ever so much.

[dharmic]

I got good results with a 6mm (1/4") two flute cutter in 4.5mm polycarb on the weekend. 1500mm/min feeds for adaptive, 800mm/min for full depth slot cutting, spindle at 8000rpm. Ramped in instead of plunging. Very clean finish, I reckon the trick is to get those RPM down nice and low. Next time I'll wind it down to 6000rpm and see how I go.

[skrubol]

Also, if it's not a hygroscopic plastic, using mist coolant can help a lot.