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After my variable speed router broke yesterday I needed a fast and inexpensive solution to slow down the speed of my routers. I wired a 600W dimmer switch to a receptacle and a plug and now I can slow down the speed of any router form 0-Max.

Craig, you are up and at 'em early today, Good morning.

Being an electrician, makes me wonder at the math behind this setup? Without getting off my duff to check the amperage consumed by a router, I'm guessing it'd be much higher than 600 watts.

I'll try to revisit this after checking the amp requirements. Glad it's working, just don't want you to burn your router up or your shop. Have a good one.

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Bruce, thanks for pointing that out, I should have clarified. Since I am only running low amprage routers 5amps 115volts a 600 watt dimmer works. 5amp X 115v = 545watts, unless there is something else I'm not understanding. For routers with higher amps you'd need a dimmer with higher wattage. A lower wattage dimmer works on higher amp routers but you would run the risk of burning the motor out quicker.

Craig, this is the first time I even heard of a low amperage router.

Here is a standard Heavy duty router, my PC 690, it runs at 11 amps with 120 volts, hence, 1,320 Watts or Voltamps.

Just checking, because it didn't compute in my electrician brain.

This is a similar equation to heating blankets. Some of those run at 875 watts 120 volts. So even those require a heavy duty dimmer, or 1,000 watts. Some folk use a router speed control and they are cheap, but I've never had one.

I've rarely ordered from Harbor Freight, but if I do I'm gonna try one of those router speed controls. Well, just trying to keep you or others from burning things up. Off to work...

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You electrician types can probably better explain this than I can, but it is my understanding that a modern dimmer switch is not a true rheostat, but that it trims the amplitude of the current -- or something like that? This way, the dimmer switch is not having to act as a heat sink, or so I've been told.

I hadn't really thought about the effect on a power tool as far as current goes. I have a dimmer switch setup the same as ctholden describes. Originally I assembled it to control the temperature of an electrical element (a charcoal starter) that I used for my bending pipe. But I also have used it to regulate the speed of a router. Didn't use it for more than a few minutes at a time like this, so I guess I dodged the bullet.   Even so, though, if a router has a variable speed control, how is this accomplished without increasing amperage?

Best,

Michael

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Live to Play, Play to Live

A better way to speed control tools and to control heat blankets, etc is a
Variac. You can find them on Ebay for $50 or so or at your local electronics
surplus store for less if you're willing to make your own box for it.
-C

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Freeborn Guitars
and home of BeauGuard©

The 1000 watt dimmer is considered commercial and are not cheap. $25 or so. They are used primarily to control incandescent lighting and heat up. The thousand watt variety has a finned aluminum coverplate with a knob in the center. So they are actually burning the power that otherwise goes to the lamp, causing it to dim.

I remember my Mom using her old Singer sewing machine, and that footswitch always intrigued me. I bet they'd work to control a router too, but not steady like a real variable speed switched tool.

Now that I think about it, I saw a young violin maker from Montana, using a Singer foot control on his Dremel tool. Wonder what the amps are on those, not much I'd bet because the motor on a sewing machine is quite small.

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[QUOTE=Bruce Dickey]
This is a similar equation to heating blankets. Some of those run at 875 watts 120 volts. So even those require a heavy duty dimmer, or 1,000 watts. Some folk use a router speed control and they are cheap, but I've never had one.[/QUOTE]

Hey Bruce! I use the router speed control with my blankeee...but this thread got me thinking...could that same control be used to slow down a buffer, like for using a radius dish on one side?

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Larry, that's a good question, which is beyond my knowledge. Time for a good ol' electrical engineer to step into this conversation. Wirenut_2

Until I started doing electrical when I was twenty, I had no idea how much there was to this stuff. On my first house I put in a relay system 24 volt on one side, 120v on the other. You could stand at one of four rotary switches and turn 12 lights on and off at once or individually, all through the house. The beauty of switches was it was run on tiny bell wire. You could have ten switches to one light if you wanted.

Then came the misunderstood 3 way circuit, which can be wired at least four ways. I know a fifth way, but it doesn't meet code. And then there are all the other areas which I know little about, expecially three phase and huge commercial systems, and electronics. Sheesh. You need an expert in each field.

Best to stay with what you "know you Know", you know?Bruce Dickey38832.4843287037

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I don't think you can use it on certain motors IE capacitor start?

Just for fun, I tried my router speed contoller (AKA heating blanket controller)on my drill press. The controller got quite hot. (maybe under rated)

Use stuff correctly!

[QUOTE=L. Presnall]I use the router speed control with my blankeee...but this thread got me thinking...could that same control be used to slow down a buffer, like for using a radius dish on one side?[/QUOTE]

On a universal motor (one with brushes), yes; on an induction motor like is probably on your hugongus buffer, no. You want a Variac (variable voltage transformer) for that.

Ah! Thanks Jay! I knew it was too good to be true! Here's why I wanted to know...I wouldn't consider this at regular buffer speeds!

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Dimmers from the home depot and such are made using chopper circuits - it chops the line voltage into a series of on-off segments - put a typical volt meter on the output of a dimmer and it always reads 115v, yet the light or in most of our cases the blanket, is getting less voltage. Its being chopped so fast that the meter circuitry cant keep up, and all it will see is 115.

Is it possible you arent using a true router, but a lam trimmer ??? Way less current, most are 2.5-3 amps, thats only 450 watts or so.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Larry, you need a jackshaft for that big ol' sanding dish. A jackshaft allows you to gear down your speed while upping your torque, not that you need more torque, just a slower machine to sand with.

I thought of doing just what you did Larry for one reason, to allow the dust to remove itself from the premises without filling the cavities of the sand paper. It may be a non-issue, since I've not built mine yet.Bruce Dickey38832.7208333333

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A variac will not control the speed of an induction motor. The synchronous speed of an induction motor = alternations per minute (7200 at 60 Hz)/ number of poles. 2 pole=3600 RPM ,4 pole= 1800 RPM , 6 pole=1200 RPM, 8 pole=900 RPM However induction motors must have a certain amount of slip to allow current to be induced into the rotor winding. So the motor actually runs a bit slower than its synchronous speed.
The only way to control speed on an induction motor is to control frequency. Drives are available, but they are not cheap basically the drive rectifies the AC power into DC power then chops it into pulses at whatever frequency is required then filters the electrical spikes into a decent waveform.
Special induction motors with wound rotors are available and their speed can be controlled by a rheostat in the rotor circuit. Once again special and expensive.
Universal motors ( think drill or router) can be controlled by a variac or dimmer as long as the controling device has a current rating greater than the full load current of the motor being controlled.
I hope this helps.

Al


A Peebels38832.7814814815

[QUOTE=A Peebels]
Universal motors ( think drill or router) can be controlled by a variac or dimmer as long as the controling device has a current rating greater than the full load current of the motor being controlled.
[/QUOTE]

So, if I understand you correctly (and to try and put it into terms that I can understand), if, for example, I have a 10 amp router that I'm controlling with a 15 amp dimmer, I've got 5 amps of buffer, so to speak, and I don't have to worry about overloading the router's motor?

Best,

Michael

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Live to Play, Play to Live

Bruce, this is actually from Kathy Wingert's site...I wanted to try it, but I'm afraid...

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You got it. Except the dimmer is the component that would fail first.

AlA Peebels38832.7891319444

[QUOTE=Bruce Dickey] Larry, you need a jackshaft for that big ol' sanding dish.[/QUOTE]
O.K., I give, what's a jackshaft? Sounds like something I got from my last employer.

[QUOTE=Terry Stowell] I don't think you can use it on certain motors IE capacitor start?[/QUOTE]
The catalog listings I've seen for those outboard speed controlers do say that they can't be used with soft-start routers.

Careful, I seem to remember that 'soft start" P/C cannot use variable speed

The Jackshaft is a belt-driven speed reducing shaft.

Say your motor is going 1700 RPM and you put a normal pulley set up on it 2 inches to 4 inches, then your speed is cut. Insert a Jackshaft and effectively do it again, it drops the output rpms again.

We use this on the big sanding dishes to drop the speed to around 100 rpm, which makes it safer to use and gives it more torque.

If you want to see one, here it is.



For any newbies who haven't found the Jigs and Tools section of the OLF, go here:

OLF jigs and tools section

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Bruce, thanks very much. Do you (or anyone else) know of a book or other tutorial that explains a formula for doing this type of thing? I've got no experience with mechanics and I'd like to learn more.

formula - its pretty simple ratios - take the rpm of the motor, say 1800, and on the motor is a 3 inch pulley. If you now drive a 6 inch pulley, the speed ofthe shaft with the 6 inch pulley is 3/6, or 900. If you use the jackshaft, or intermediate pulley (s), just do the same ratios to find your final rpm.

So for the picture above it would look something like this :

1800 rpm - 3 inch on motor to 12 inch on jackshaft, thus jackshaft spindle is turing 450 rpm. Looks like about 1.5 inch then on the JS to about 4 inch on the shaft driving the bowl - so 450 x 1.5/4 = 168.75 RPM.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Tony,

Got it. Thank you! I can sleep now.