How to run a fixed speed Mortiser at a slower speed?

Question

I have had a Multico PM12 for over twenty years and it has faithfully served me both for mortising and as a drill press. My workshop is not big enough to fit in both.
Very recently I needed to use a 45mm diameter Forstner bit to cut 12mm deep recessed holes into solid oak. I tried this in the mortiser and this works OK for a few seconds (say 2mm depth) but after that it gets too hot and burns the sides of the hole being cut. I can cut them very slowly letting the bit cool down but with 24 to cut it takes ages. If I cut for too long, cleaning up the burn marks is very time consuming and difficult, but a drum sander in a electric drill does help.
This burning is obviously because the mortiser speed is around 2500 rpm which is ten times too fast for such a large diameter bit (250 rpm max for 45mm Forstner bit in hardwood).
Does anyone have any experience of using an AC frequency reduction device to slow such a machine down. If so can they recommend a make and model. How slowly would I be able to run the motor and what would the current increase to?

rjuzzle · Answer

I'm not sure if the wood working SE is the place to post this question, but ill give you my experience. The best way to deal with this is hands down get your hands on a drill press. That being said there are motor controllers that you can buy that can change the speed of your motor using Pulse Width Modulation (PWM).
The problem you may run into though, is once you start dropping speed, you start reducing the amount of torque you'll get. Drill presses with their pulleys maintain certain torques at given RPM's due to the pulleys.
Dimmer switches are another way you can play around with motor speed but I would highly discourage that, the slightest bit of load will need to be balanced out by changing the dimmer, causing a lot of multitasking which will lead to injury.
Personally I would try to get ahold of someone to with a drill press, even if it costs you a couple beers.

How to run a fixed speed Mortiser at a slower speed?

One Answer

Add your own answers!

Ask a Question