miter saw speed control, 120vac, ac-only, brush motor

[dseman]

Guys,
I have a Dewalt 12" miter saw that uses a 120vac,single-phase, brush type motor. It turns at 4000rpm, which is fine for wood cutting. I want to reduce the speed to 1700rpm, maintain the torque, and with a blace change, cut metal with it (similar to dry-cut saws). I've tried a router speed control, which worked fine on ac/dc universal motors found in my portable drill, circular saw, and angle-grinder, but it does NOT work with the miter saw. The only thing I could find is that Dewalt says it is ac only, but it does have brushes that can be replaced in the motor cap. How can I control the speed on this thing?
thanks a lot,
Dave
dsemanus@yahoo.com

 

[jbartos]

Suggestion: It is not a problem to reduce the speed of the motor. A variable frequency drive could reduce the speed. The problem is how to cool the motor that will be loaded with the same torque. Maybe a cold-water cooling hose turns around the machine could do it.

 

[dseman]

Jbartos,
Thanks for the reply. Two questions: 1.) I thought VFD would only work with a 3phase motor, this is 1-phase, 120vac. Are you saying that VFD would work here as well? Any idea for manufacturers and cost for this application?

2.) I believe that with a small muffin fan located at the far end housing of the motor I can solve the heat problem of the motor running at 1700rpm instead of the intended 4000rpm. There is a fan mounted directly on the shaft of the motor as it is right now, so the muffin fan would supplement that.

thanks for any future responses!
-dsemanus