Gerd,
Again I apologize for typing in English. If I try German, it costs me so much time and using a "Worterbuch" for nearly every word.
You have done much for this commutnity with your program and this hopefully a a manner to thank you !
Lots of topics already in Woldig's answer.
The keywords in milling acrylic are AVOIDING HEAT !! (Bis

)
There are2 types (which cannot be distinguised from each other on sight (for me):
1. Extruded
2. Casted.
The melting point of extruded is about 100 degrees, from casted 130 degrees.
So if milling casted acryl, there are nearly no melting problems. Problem is thats it's fare more expensive.
For small quantities this is not a factor (and even consider it strongly for greater quantities !!!).
If you want to mill extruded there are the following possibilities:
1. Cool with water. Add 1-2 drop(s) of detergent to do the dishes, to make the water stay where it should be. To avoid a mesh with the water I put on my MDF underplate a piece of plastic. On this plastic a piece of (1mm or so) cardboard and above this the acrylic material.
The has the advantage that you can freely spray the water..., mill into the cardboard a little bit and nevertheless keep your MDF underplate free of water. Spirits in stead of water is another possibility.
2. The chip which is milled off removes the heat for a great deal so remove them as much as possible with a brush.
3. Since a mill which isn't nearly moving generates only heat and no chips..., a relative "fast" speed over the material is necessary. With our weak mill this means 10-15 mm/sec. The depth should be adepted to that speed, so start with e.g. 0,2 mm per round. Increase as your experience grows. So speed through the material presedes over depth !
Intrigueing that Woldig can mill e.g. 3 mm in 1 procedure ? Did I understand that well ? Od course if someone can mill all material depth in once it's preferable. Any info Woldig ?
4. The best way to remove chips is a mill with one (!) flute. Also of course less heat here. Sharp and HSS.
5. Motorspeed as low as possible. Most here use the Kress 850 or 1000, so 10000 r.p.m. is (alas) the minimum. In fact it should be less be happily we use small mills (2 or 3 mm diameter) the with smaller mills the spindle speed can be higher then with increasing diameters.
6. Cooling with a constant air flow. I see this in my "acrylic-shop" and that does ALL even with extreme speeds and depths ! A (small) compressor is necessary.
7. In shops for plasics etc. you can buy polish (if necessary).
8. Glueing goes i.m.e. the best with dichloromethane. With a syringe and a needle you can put a this over the surface and put the parts toegther. Within a minute is is fitted and no dirty glueing effects can be seen on clear acryl. MIND !it's toxis so do it outdoor. It's also very, very volatile so do plan your work otherwise it's away before you are ready...

. Somewhat slower with Chloroforme. All warnings the same. Apotheke.
9. Do a search on
www.cnczone.com. See also:
http://www.deskproto.com/gallery/perfume.htmHope this helps a little bit,
Hessel