# How can I slow down RPM on my bench grinder ?



## joecaption (Nov 30, 2011)

Running a file over a wire wheel is a very bad idea. It's going to dull the file.
Use navel jelly, a hand file card or if there's lots of them there a way to do it with a battery charger.
Trying to slow it down is going to reduce the torque and HP.
I've used 3600 RPM wire wheels for removing rust for over 50 years and it's never been an issue.

http://www.bing.com/videos/search?q...=removing+rust+with+battery+charger&FORM=VDRE


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## SeniorSitizen (Sep 10, 2012)

Both wire brush and speed control on that motor are bad ideas. Try *The Works *acid toilet bowl cleaner on a test area 24 hours to remove rust. If it doesn't do the job for you the toilets always seem to need cleaning.


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## taylorjm (Apr 11, 2013)

Look at speed controllers for routers. I've seen those around. My grinder, also from sears has a speed controller built in, and I love it.

http://www.harborfreight.com/router-speed-control-43060.html


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## Cedrus (Feb 25, 2011)

Thanks for the replies. I was not clear in that I have a wire wheel for the files and was not going to use a grinding wheel.

I will look at The Works. I have used hydrochloric acid (for pools) and it did some good but they rusted again in a day for so. Guess I should have sprayed with.........??


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## joecaption (Nov 30, 2011)

There is no wire wheel for files, no manufacture of files would ever suggested using one.
Could have cleaned them off and just sprayed them with WD 40 to protect them.
The WD stands for water displacement


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## BigJim (Sep 2, 2008)

Cedrus said:


> Thanks for the replies. I was not clear in that I have a wire wheel for the files and was not going to use a grinding wheel.
> 
> I will look at The Works. I have used hydrochloric acid (for pools) and it did some good but they rusted again in a day for so. Guess I should have sprayed with.........??


My brother-in-law used the acid on files, then dipped in Arm and Hammer and water to neutralize then into oil then dried, it worked really good.


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## hotrod351 (Jun 15, 2012)

using a dimmer or other method to slow it down by decreasing voltage more than likely burn up the motor. i have a two speed baldor motor for buffing jewelery but its designed that way.


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## Albe (Mar 2, 2012)

BigJim said:


> My brother-in-law used the acid on files, then dipped in Arm and Hammer and water to neutralize then into oil then dried, it worked really good.


muriatic acid (is only diluted hydrochloric acid) used for cleaning masonry joints, etc works well. I'm only mention it because it may be cheaper than pool store acid and is readily available at most any box store (home depot, lowes etc) for like $12 a gallon? if i remember correctly. I second the neutralization in baking soda and then oil. 

As for a motor controller (which isn't the best of ideas I suppose) I would think a big enough rheostat would work (like an old wall dimmer). 

good luck!

Al C


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## More Power! (Aug 2, 2011)

lifestooshort81 said:


> As for a motor controller (which isn't the best of ideas I suppose) I would think a big enough rheostat would work (like an old wall dimmer).


Nope. Bad for the motor, bad for what you're working on. You have to reduce the voltage so far, to appreciably slow the motor, that there's insufficient current supply available for it to maintain speed under load. Or the unloaded speed has to be way too high. The way it's done properly is by PWM: Pulse Width Modulation. The motor is slowed by reducing the duration of full voltage, not by reducing the voltage. This way, when the motor's loaded, the current demand can still be met. 

(The explanation above is neither rigorous nor even 100% accurate, but it's close enough.) 

Jim


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## Thurman (Feb 9, 2009)

The key word here is "grinder"!!! You should never slow down a grinder. I'm not going to look up what size grinder this is and it doesn't matter. ALL grinders, from the smallest you could find at Wal-Mart, Sears, etc. to the best you could order are designed to run at a certain speed based on the diameter of the grinding wheel being used on THAT grinder. This is based on SFPM (Surface Feet Per Minute). Let's just say a 10" grinding wheel. In one revolution the outer edge of that wheel travels approximately 31.4 feet. Multiply that by the RPM's of the grinder and you will have the approximate SFPM. Now IF you go playing around with the RPM of the grinder you go changing the SFPM of the grinding wheel. Add too much SFPM to the grinding wheel and they will explode. In my 38 years of industrial maintenance I have seen this happen, not by my doing though. Slow the RPM of a grinder down and you will get build up of the material being ground into the wheel which will cause heat build up and another reason of grinder wheel explosion. Have you ever wondered why a buffing wheel doesn't work so well on a bench or pedestal grinder? Buffing wheels need more RPM's than a grinder can give. BUT--grinding wheels should NEVER be used on a buffer. That's why most buffer machines have shaft diameters that will not match up to most grinding wheels and vise/versa. As far as cleaning files--nothing beats a good file card and elbow grease. I have some files that I have had for over 30 years. I still use them, they cut well, they have no rust, and I keep them clean with a file card.


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## PaliBob (Jun 11, 2008)

Thurman said:


> . . . . and I keep them clean with a file card.[/QUOTE





Thurman said:


> ]
> For anybody who is not familiar with a file card, this is what they look like:


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## PaliBob (Jun 11, 2008)

To restore a number of heavily rusted files I would use a three step process:
1) Dunk them in a Hydrochloric acid e.g. LCR. For really heavy rust, wear rubber gloves + eye protection and scrub with a wire bristle brush.
www.youtube.com/watch?v=tjf7gmTBXOs
2) Wash and dry thoroughly then brush with a File Card. The steel brushes on the File Card will clean any remaining crud out of the grooves in the file.
3) Finish with a spray of WD-40 and blot out any excess
• I get my WD-40 in a Gallon can then transfer it to a plastic WD-40 brand 1 qt plastic spray bottle. That size has been discontinued. Now Amazon just carries the pint size. It does still have the adjustable stream or spray nozzle.


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## Cedrus (Feb 25, 2011)

Thanks again....I have given up the idea of slowing down the wire brush/grinder and will use the file card brush ideas as some have suggested.

Glad I asked. You probably saved a finger from damage and perhaps motor damage also.


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## PaliBob (Jun 11, 2008)

PaliBob said:


> . . . Dunk them in a Hydrochloric acid e.g. LCR.. . . .


 LCR is a Brand name that has a lot of competition that may be just as good or better.
Here is an LCR Ad: They also come in much smaller sizes.


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## yuri (Nov 29, 2008)

Slowing down motors also causes problems as they are designed with a cooling fan which needs to spin at full rpm to move enough air to cool the motor. Slow it down and the motor overheats and bearings fail quickly.


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## Toller (Jan 2, 2013)

Thurman said:


> ALL grinders, from the smallest you could find at Wal-Mart, Sears, etc. to the best you could order are designed to run at a certain speed based on the diameter of the grinding wheel being used on THAT grinder.


 Up to now I have been very happy with my 1800rpm 8" grinder. But now I know it doesn't work. Or is it all the 3600rpm 8" grinders that don't work?

I have used a wire wheel to take rust off a file; it might be suboptimal but it is fast, does the job, and leaves the file working just fine. The soft wire on a wheel should not appreciatively dull a hardened file. (maybe it is the 1800rpm...)


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## PaliBob (Jun 11, 2008)

Toller said:


> I have used a wire wheel to take rust off a file; it might be suboptimal but it is fast, does the job, and leaves the file* working just fine.* The *soft* wire on a wheel should not appreciatively dull a hardened file. (maybe it is the 1800rpm...)


When files lose their sharpness they are worn out.
There is no good reason to make them wear out faster.
I would not call a wire wheel *soft*.

If I held the blade edge of a very sharp knife against a rotating wire wheel it is going to degrade the sharpness of that blade.
Same for a file.
.


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## Toller (Jan 2, 2013)

PaliBob said:


> I would not call a wire wheel *soft*.
> 
> If I held the blade edge of a very sharp knife against a rotating wire wheel it is going to degrade the sharpness of that blade.
> Same for a file.


The wire has to be soft; if it was hard it would go to pieces very quickly. Soft will wear out, but at least you don't get shrapnel of wire bits. Well, fewer anyhow.

Sure it degrades the file, but doing anything to file (using it, or getting rust on it) will degrade it. Putting acid on it sure isn't good for it. The acid will preferentially attack thin parts first, like the sharp edge.


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## jeffnc (Apr 1, 2011)

joecaption said:


> The WD stands for water displacement


That's correct, and not many people know that. There are better lubricants out there, because that's not really what WD-40 was designed to do. Sorry to get off the subject, but it's true


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