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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?

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    Hi Steve, you're in the UK I presume from the use of metric in your Q? Assuming you are I would highly recommend getting a basic hand-operated drill stand, the secondhand market is choc full of them in the UK. One of these'll will be handy for any job like this and they can be small enough to be stored out of the way on a shelf when not in use.
    – Graphus
    Commented Dec 4, 2020 at 8:38

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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.

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    Thanks very much for your answer. I would go out and buy a drill press tomorrow but I have nowhere to put it in the workshop except where the morticer is and as the morticer has served as both a morticer and for 95% of my drilling needs I think it the better use of workshop space. Having just said that I wonder if I should look for a portable bench mounted drill press that I could only get out when I needed it?
    – Steve Brooker
    Commented Dec 4, 2020 at 8:00
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    I don't know the specifics of this machine, but I'm going to assume it's run by a typical induction motor. If that's true, using a dimmer is a really bad idea. The free running speed of an induction motor is determined by the frequency of the sine wave, not the voltage. To oversimplify a whole lot (and lie a little bit), using a dimmer would slow the motor while it's loaded by making it less efficient, which will cause the motor to heat up a lot more than it's designed for.
    – Gern Blanston
    Commented Dec 4, 2020 at 14:10
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    @GernBlanston -- can you suggest a google keyword search that would point someone in the right direction to better understand your comment? Among my many questions: Are dimmers all the same in dropping voltage? Are those rotary controls that often get sold as router speed controllers the same sort of thing? Thanks in advance.
    – Aloysius Defenestrate
    Commented Dec 4, 2020 at 18:19
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    youtube.com/watch?v=tXJOtWPPRwE, Here is a good Youtube video that explains. Yes, dimmer switches and most of those speed controllers work off the same principles. The main component that makes the power pulse is a TRIAC for AC Circuits.
    – rjuzzle
    Commented Dec 4, 2020 at 18:41
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    @rjuzzle Great video. And thanks for pointing me to that channel. I was in serious danger of having a productive weekend, but I won't have to worry about that now. :)
    – Gern Blanston
    Commented Dec 4, 2020 at 20:04

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