For anyone doing plastics and wondering how fast to go, I found this chart:
The plastics are on the second page. You’ll see they give a recommended RPM for the spindle. If you don’t have an adjustable spindle then you can use the math to adjust as needed.
RPM is recommended spindle speed for the size endmill you are using.
Fz is the recommended chip load per flute.
Feed Rate is how fast you push the endmill through the work.
So feedrate = RPM x Fz x No. of Flutes. That equation will get you in the ballpark so you’re not clogging the flutes, and not starving them so that they overheat.
That won’t tell you how deep a cut you can take - I don’t have the math for that one.
Hope this helps a bit - I know I stopped burning up endmills on my mill once I started using the math.