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Topic Review (Newest First)
11-03-2007 10:16 PM
oldred Not sure which dimmer switch you are using but you can't just cut down the voltage on an AC motor like you can with a DC and expect to get any service out of it. They will heat up for other reasons than just the fan running slow and if yours are doing ok then you probably are not using the rheostat type dimmer or you you are not using them very hard. The question here was "how can I slow down my electric grinders" and simply cutting down the voltage is a darn good way-- to burn out the motors that is!
11-03-2007 08:14 PM

An AC electric motor requires the cooling that is generated at the speed it runs normally. This is achieved by simple cooling fins usually pressed onto the main shaft. If a potentiometer or rheostat is hooked up, "in the hot side of the 110V power wire works easily enough," the time the motor runs at a slower speed needs to be short. Over heating could be checked by physically checking the housing with your hand to feel if it is hot. Normally it will create heat, but if it is to hot to hold your hand on it for more than a few seconds, it is over heating. If you smell a sort of chemical odor emanating from the grinder, the amateur coating is burning and that means it is over heating as well. All of the different size bench grinders I have owned and still use, I have outfitted them with a basic dimmer switch for the interior lights from 24V Diesel application and they still work. Although I have the switch bypassed with another wire with an On-OFF switch for use during normal operation.
11-03-2007 05:34 PM
123pugsy I use a hammer drill to spin my 4" wire brushes with a 1/4" shank.
The speed is good at 2700 RPM's.
11-03-2007 05:17 PM
Bryan59EC Have ya thought of this??

Locate an old variable speed polisher/sander and use your wire wheels on that.

I have an old polisher that I did just that to.

Those grinders spin pretty fast and will wake yer hiney right up when it catches the cord . I have also managed to grind divots into various parts of my anatomy----this generally has some sort of painful stoopid idiotlesson attatched to it.

11-03-2007 04:55 PM
Rob Keller
Originally Posted by dinger
A retired machinist friend of mine does this by hitting the on switch, let's it slow down, hits the switch again...on-off, on-off. Makes me crazy watching and listening but seems to get the job done.

Just when you think you've seen everything someone comes up with a new way to abuse tools


I will have to check that out

I used the Router thingy today & it was nice & a PITA too but with that long shank die grinder geese 'O pete it spins up to 25,000RPM s.

When the brushes say up to 4,500.

I will have to get some good brushes for that thing!

11-03-2007 09:44 AM
dinger A retired machinist friend of mine does this by hitting the on switch, let's it slow down, hits the switch again...on-off, on-off. Makes me crazy watching and listening but seems to get the job done.
11-03-2007 12:56 AM
CDJr Rob, I bought a lil 4" GMC variable-speed grinder at Lowes for that same reason. I already had 3 grinders but they were all single speed and I got tired of digging wire out of my legs lol. This thing only cost like $30, so naturally I assumed itd be a disposable, but much to my surprise, it finished the job I wanted it for and Ive put it through its paces many times since then and its never missed a beat. Id hafta say its the best $30 tool Ive ever seen
11-02-2007 09:10 PM
Rob Keller And if it were to work on DC ...

How much DC volts & amps?

Just outta curiosity

11-02-2007 05:43 AM
Huskinhano Electric motor 101. Split phase 120 volt motors are "induction" type motors with the speed controlled only by the frequency of the current. If it has brush type motor, you should be able to vary the speed. I know years ago, they use to sell speed controllers for drills, we had a couple in the shop and worked well. Most hand tool motors with brushes will work on DC also!
11-02-2007 03:25 AM
Rob Keller
Originally Posted by 79C10
have you tried holding your thumb on the grinder wheel to cause speed reduction via friction ???

I hope not.
I was expecting a response like this much earlier

smart arse! {better than a Dumb one}

SCROT Not until Old red here got me a looking {I love "how things work I can get lost there for daze}

New way

Old Red Don't you hate when these guys sneak this new technology in there & forgot to tell us about it?

I an 100% on this .

We all miss ,Doc I was going to post this to Repeaterman but I did not want to exclude others .

It is a Forum

I don't know if he spends a lot of time here

I picked up a Router Speed Control & will give it a shot It has to be better than White Knuckled Grinding.

Hey maybe I'm onto a new "Extreme Sport"
If poker is a sport this could be too.

Thank you all!

So will the "new way switch" work?

11-01-2007 07:36 PM
oldred Ok, this thing is indeed just a simple variable resistor that drops the voltage and therefore not suitable for an AC motor but after a bit of research I find that not all light dimmers are created equal and the rheostat type is considered the "old way" of building them but they are still very common, the one I just cracked open was purchased less than 6 months ago. Seems the "new way" (power saver type) to build them is about the same principle as a motor controller and it would seem that as long as the rating is not exceeded it might work but it would have to be this newer power saver type.

This is the ones I was familiar with (a simple variable resistor or rheostat) and I mistakenly assumed that most were still made this way. I have no idea how common these are compared to the other type but I am sure they are still very common because as I said I bought a couple of them not long ago.
11-01-2007 07:12 PM
302 Z28 AC motor speed controllers operate by varying the frequency not the voltage.

11-01-2007 06:46 PM
123pugsy I have one that you can bust open,preferably with a BFH.
11-01-2007 06:08 PM
Originally Posted by scrot
Doc is rolling over in his grave now.

The light dimmer for an AC circuit is a lot more complicated than a rheostat. Ever heard of an S.C.R., silicon controlled rectifier?
It clips off part of the AC sine wave to reduce the power.
Doc , we need you back!

I guess they come in different types- the el cheapo I have here sure looks like a rheostat inside, I very well could be wrong but there is nothing in it resembling any kind of circuit. There is a round device on the back of the switch that looks to me like a common rheostat but I could be wrong and maybe the circuit is inside I will break open that little plastic case and see what is in it, got my curiosity up now.
11-01-2007 05:51 PM
79C10 have you tried holding your thumb on the grinder wheel to cause speed reduction via friction ???

I hope not.
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