Variac as router speed control?

Question

I've got a hunch this is probably a bad idea. I bought a Milwaukee 5615 fixed speed router and I need to swing a

3/4" roundover bit (~18,000 rpm, according to Jesada). I'm wondering if I should return this fixed version for the variable speed unit, or if a 2kw variac will do the job? Dave

Lew Hodgett · Accepted Answer

You don't want to go there.I could give you a long explaniation why, but it's late and I'm tired. Sorry.What I suggest is you consider something like a table mounted PC 7518.A 3/4" rounding over bit is nothing to fool around with in a hand held router, IMHO.You are probably going to have to probably make multiple passes anyway, so a table makes it a lot easier and safer.HTHLew

Wilson Lamb · Answer

Well, I just got up.The Variac is a great variable voltage transformer and good for many things...I might want to buy yours.The trouble with the router is that reducing the voltage to the router will reduce the current the motor "can" draw as it loads down in a cut.  With limited current it will sag badly and slow way down...more than you want.The solid state speed controls are entirely different. They control by actually turning the voltage off and on rapidly.  The great thing is that they also incorporate a feedback system that senses motor speed and increases the voltage as required to maintain the speed you want.  Just run your variable speed drill at low speed and take hold of the chuck.  You'll actually feel  and hear the torque pulses change as you apply load!So there you go.  Buy the speed control.  They are cheap ($12 for mine).  Of course having the control built in is great.  I'd do the exchange if I could.Wilson

Juergen Hannappel · Answer

While a variac is great for fan motors, especially if you go threephase, it's not a good idea on cutting tools. Go for the variablespeed unit, it will anyway be cheaper then the variac.

Robatoy · Answer

The 5616, the 2.25 HP VS bigger brother of the 5615 (I own both) is barely adequate for thr 3/4" r bit... depending on material. The variac does nothing for 'speed' as such, it just makes it weak, which is fine for a light bulb. You will seriously affect the 5615's ability to cool itself as well.

Interious · Answer

I kind of figured purpose designed speed controls essentially act like an intelligent constant current source. I thought I would ask about the variac anyway just to rule the option out with certainty.

I think I'm going to get the 5625-20 and put it in a table for this job. My experience is with a wimpy old craftsmen router and small bits. Lots of learning to do.

By the way--I bought a Bosch 3/4" roundover bit at Lowes. Should I return it for a Whiteside, CMT, etc.? MDF is the current medium.

Thanks to all for interesting responses. Dave

Wilson Lamb · Answer

The controller is not a constant current source, it's the opposite. Constant current will give constant torque, so you'd go to max spped with no load and stop as soon as the load torque corresponded to the current set in the controller!  It IS a (nearly) constant SPEED device.  Current can rise to whatever is needed to maintain speed, or until the motor or controller blows.  With the motor locked, such a controller can deliver full voltage to the motor, at high current, frying it quickly.WL

Interious · Answer

Wilson,It's a long time since I've studied current and voltage source theory.I completely take your word for it. Makes sense. Dave

Thomas Bunetta · Answer

I have two Variacs... I wonder what they're worth. I was thinking of sellingthem on Ebay, I got them from an estate sale (an electro-chemical engineer'sestate)Tom

Variac as router speed control?

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