Need help on picking a new spindle for plastic

[dbtoutfit]

I have a Z20 rotozip.

The problem is it's just too fast to mill plastic with out melting.

The Z20 comes with a virable and can not work with a router speed controller. I have even removed the speed controller but when I plug it into the router speed controller the Z20 just pulses, it's not smooth turns.

I am running the machine as fast as it will allow. So speeding up feedrate will not help as I have already done this plus tuned the steppers to their top speed.

I would like to purchase another router the same general size as the rotozip so that I do not loose any gantry travel.

Could someone suggest a good router for milling all that the Z20 can but can also be slowed down to mill plastic?

Thanks