CNC Engraving plastic some pointers

[Wizpic]

I have a little CNC machine that I use to make PCB'S, I've mastered this now and get great results even double sided ones. I'm now looking into cutting and engraving plastic case's.
Now I've had ago at cutting out a hole for the LCD and turned it up-side down and milled out a small amount so that the LCD sits closer to the front(have considered gluing clear plastic on the inside to help protect the screen). I would like to have ago at engraving text and stuff on the front of them again had a quick go but results where no so good I may have been using the wrong tool this was a .2mm tool that I use for the PCB's.

Q1. What's the best speed rate and router speed to minimize the plastic melting ?
Q2.  best tool for cutting and if it can be done with clean results ?
Q3. what type/best tool or end mill for engraving ?

Has any body else tried it ?
Just after some advise and your methods that you use if you have done it

[pickit2]

speed would depend on your plastic, Perspex likes a high speed cut.
you have to make sure the tool gets the chips out of the way, or it will melt and stick back.
I have 1, 2, 3 & 4 flute end mills, I usually try a few test cuts, before committing final cutting speed.
the last front panel I cut in clear Perspex two layers with Vinyl text sheet, cut on wife's scan & cut.
it would have been good Vinyl on Plastic too. 

[lou]

Years ago I used a hand operated engraver for equipment name tags that were  plastic.  I can not remember the name of the machine, but it used a single straight flute carbide cutter that was about 1/8" in diameter. The tip of the cutter was ground off at an angle so the the cutting lip is off center.  The amount of off center determines the width of the engraving. The speed of the cutter was very high RPMs (I know that not much help).  It seems to me that the chips were cleared by the cutter being a single straight flute.
Can't figure out how to add a photo, just go to eBay and search for carbide engraving bits.