Hot Rod Forum banner

How can I slow down my Electric grinders?

16K views 29 replies 16 participants last post by  oldred 
#1 ·
I was wondering if there is a way to slow down my electric grinders.

maybe a rheostats?{if I got the right word}

I use the grinders with wire wheels to clean up grease and rusty stuff & some times they are just spinning WAY too fast.

Can this be done safely?
Can this hurt the tool?
Running it too slow or something?






:thumbup:
 
#6 ·
Rob Keller said:
What Happened?




:thumbup:

It was a couple of years ago so my memory is a bit fuzzy, but I know it didn't work on my router so I tried it on an electric drill or something else just for the heck of it. Well of course with my luck it worked on a tool with a built in speed control on the switch and not on the tool I needed it for.
 
#8 ·
On an AC motor it is not as simple as cutting down the voltage and if you do that it will cause the motor to overheat. A DC motor will run fine on lower voltage and that is why DC is used when a variable speed motor is called for on most machinery. An AC motor speed controller, although fairly simple, is quite a bit more than just a light dimmer which is nothing more than a rheostat and a light dimmer should never be used to control the speed on an AC motor, it can cause damage to the motor. I have one of those HF motor controllers and although it will reduce speed it also reduces the power a LOT.
 
#10 ·
I have used a router speed control with my 2 and a half horse power router for years...never had a problem with it...yes the motor is AC. I did not use a HF controller though...I got mine at Sears. I have never tried to slow down a grinder with it...but I don't see why it would not work for that.
 
#11 ·
Henry Highrise said:
I have used a router speed control with my 2 and a half horse power router for years...never had a problem with it...yes the motor is AC. I did not use a HF controller though...I got mine at Sears. I have never tried to slow down a grinder with it...but I don't see why it would not work for that.

Nothing wrong with that, it is for an AC motor and should work with most tools as long as they don't exceed the rated current on the speed controller.

The Harbor Freight speed controller is for AC use also and will work with most AC motors but if you open up either one of these controllers you find that it is a heck of a lot more than just a simple rheostat. Using a light dimmer (which appears to be a rheostat) would be no different than using an extension cord that is too long which will cause a voltage drop and can damage an AC motor.
 
#13 ·
fitzwell said:
Foot control off a sewing machine?

I think those things use a DC motor, I think anyway? :confused:

That little outfit from HF works pretty good and I use mine a lot, well I did anyway until I closed a door on it and broke the dang thing. :mad: I think they are on sale right now for about 10 or 12 bucks so I am going to get another one, they will handle some pretty big stuff and I found mine to be especially useful for my electric die grinder.
 
#14 ·
Doc :pimp: 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? :confused:
It clips off part of the AC sine wave to reduce the power.
Doc :pimp: , we need you back!
 
#17 ·
scrot said:
Doc :pimp: 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? :confused:
It clips off part of the AC sine wave to reduce the power.
Doc :pimp: , 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 :confused: I will break open that little plastic case and see what is in it, got my curiosity up now.
 
#20 ·
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 :evil: 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.

http://home.howstuffworks.com/dimmer-switch1.htm
 
#21 ·
79C10 said:
have you tried holding your thumb on the grinder wheel to cause speed reduction via friction ??? :thumbup: :evil: :p

I hope not. :pain: :nono:
I was expecting a response like this much earlier :D

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 :pimp: 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 :confused:

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?






:thumbup:
 
#22 ·
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!
 
#24 ·
Rob, I bought a lil 4½" 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 ;)
 
#25 ·
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.
 
#26 ·
dinger said:
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

LOL :rolleyes:


CDJr
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!





Rob :thumbup:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top