Cutting plastic for first time, perhaps I am going wrong a tip or two be great thanks

[phill05]

I have to cut some 10mm to 10.8mm grooves at a depth of 39mmin HDPE. I am thinking of the following:
10mm 4 tip carbide end mill 50mm long
4000 rpm which is my max spindle speed x and y federate 1800mmper minute 2500mm max for my mill
300mm federate in the z cutting at 3.9mm per pass 10 passes.

I have just been cutting Nylon 6 and found 1 or 2 flute upcut works best it throws the chips out great no need for airline just use vac to clean up.

Phill