slowing down mag drill rpm

wippin' boy · Feb 5, 2018

I've got a mag drill running about 500 rpms. I bought one of those cheap scr variable voltage speed controls.
I haven't cut open the cord going to the motor yet but I'm assuming it's L1,L2 and maybe ground.
is this going to work?
how slow can I run this without burning it up?

ewlsey · Feb 5, 2018

What's the question exactly? You can use a variac to slow it down. It's the same issues as any other variable speed device. Less RPM is less power. Less RPM is less cooling from the fan.

That said, the newer mag drills from Milwaukee and others have built in solid state variable speed. Probably a triac based circuit. I don't know what range they allow on those.

atomarc · Feb 5, 2018

I'm not sure how your speed control device might work but you sure as heck don't want to drop voltage or whatever to the magnet..right!

Stuart

rons · Feb 6, 2018

wippin' boy said:
I've got a mag drill running about 500 rpms. I bought one of those cheap scr variable voltage speed controls.
I haven't cut open the cord going to the motor yet but I'm assuming it's L1,L2 and maybe ground.
is this going to work?
how slow can I run this without burning it up?

I would not know which "cheap" one you have.
You would be altering the phase angle of a current passing device. Whether it uses back-to-back SCR's or a TRIAC. The question will be how slow can you run the drill and have it not stall. Depends on drill and what material you are drilling through. Plastic or wood, probably around 1/3 to 1/2 speed. With metal don't expect much. I like the idea of using something like that to start a hole or have a soft-start with a wood router to prevent that "kick" when it starts.

9100 · Feb 7, 2018

Depends on the type of motor. If it is shunt wound, you need to keep full voltage on the field and vary only the armature voltage. If it is series wound, as a practical matter you cannot control it that way. You can slow it down, but all you are doing is weakening it and when you put a load on it, it will slow down or stop. As atomarc says, you will have to separate the magnet supply.

I think the best answer I can offer is to get help from someone who really understands motors. You are not likely to get decent results by plugging it into a light dimmer.

Bill

Steve in SoCal · Feb 7, 2018

The big honkin Milwaukee I have has a var-speed for the motor. I know not what you want to know, that said, "most" of the bigger motors are two speed. Is that a possibility?

Steve

Chip Chester · Feb 7, 2018

Is something like this in-line gear reduction unit beefy enough for your use? It will take up some Z.
Hougen Drill Speed Reducer - Ohio Power Tool

wippin' boy · Feb 8, 2018

I'm not going to reduce magnet voltage
the drill motor is the same sort that come with variable speed in higher priced units so I suspect it is the "right kind"
the cheapo device is like this

1W AC 22V 75A SCR Voltage Regulator Speed Controller Dimmer Thermostat | eBay

says it's scr based
looking to slow it down from 260 rpm to something slow enough to just start a smallish tap

a 1500 dollar Unibor will do it but that's out of my price range but I'm am planning to buy a 2 speed drill with similar wattage.

right now I just do it by hand by sticking a drift in the three jaw chuck tightening hole( what would you call that? the pinion hole?). but im getting old and lazy

DDoug · Feb 8, 2018

Have you tried it at 500 rpm ?

Mine pulls down pretty quickly under load, with a large drill bit on it.

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