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can i modify a bench grinder to turn slower?


jmkeuning
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It's a low-end Delta.

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if the motor us below 1HP (very likely) you MAY be able to control the speed with a router speed control --

 

my experience with this kind of rig is that, the lower the speed, the less consistant the speed will become -- that is, it won't hold a steady (for instance) 100RPM, but will vary between 90 and 110RPM, in a jerky manner.

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I don't know the answer. I think I remember reading that variable speed control will work with motors with brushes; Brushless motors vsc won't work, at least that's how I remember it and my memory isn't all that good.

 

I use a converted Dremel Shoe Buffer for my pen buffing - the kind you used to see in hotel rooms. I had a local machinist convert the spindles to accept 4" buffing wheels. This is low speed and low power and easy to use for buffing. The only down side is that it won't hold up to long periods of use - say buffing more than four to six pens - without over heating. But that works for me. These buffers are sometimes found at garage sales, flea markets, etc.

 

 

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My reaction would be to fit a belt pulley instead of the wheel, then take a V belt to a secondary shaft with a larger pulley wheel. The gear ratio would then be:-

diameter small pulley/diameter large pulley.

 

However, I have a few bits of steel for shafts and a few bearings lying about the place.

 

If you are using it to grind, don't lower peripheral speeds lead to enhanced probability of wheel glazing?

 

Regards

 

Richard.

 

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My reaction would be to fit a belt pulley instead of the wheel, then take a V belt to a secondary shaft with a larger pulley wheel. The gear ratio would then be:-

diameter small pulley/diameter large pulley.

 

However, I have a few bits of steel for shafts and a few bearings lying about the place.

 

If you are using it to grind, don't lower peripheral speeds lead to enhanced probability of wheel glazing?

 

Regards

 

Richard.

 

Depending on the material being ground, yes, it could lead to glazing.

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Might be easier to get a variable speed Dremel outfit with a foot peddle "accelerator" set up.

Edited by Bearcat

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Most bench grinders will work with a variable rheostat control; there are several commercial products that fit the bill. Here's a recent ebay listing for one.

 

Should be twenty bucks or under. I picked mine up at a flea market for $5.00 used.

I'm Andy H and I approved this message.

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Why don't you explain why you're trying to reduce the speed first? As you say it's a cheap grinder, I have an idea why you might want to -- but there are better ways to accomplish what you're trying to do... PM me if you like, as there's no guarantee I'll find my way back here...

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By running the motor through a rheostat you will reducing the voltage to the motor. In order to make up for the reduced voltage, the motor will demand more amperage. This will cause the motor to run hotter. The correct way to do this is with a VFD (variable frequency drive). This will change the 60 cycle frequency that the motor runs on (50 cycles if you're in Europe) and make the motor a variable speed motor without changing the voltage or the amperage. The VFDs aren't as expensive as they used to be, but probably more than you want to spend on a low end bench grinder.

 

 

At Your Service,

Clydesdave

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That's why I use the variable rheostat Clydesdave, bench grinders are basically "disposable" products, and it is rare that I need to run one constantly for more than a few minutes at a time. I've been doing this for years for grinders as well as for Dremel tools (where the variable rheostat is built right in) and some lapidary equipment and never had a problem. If I were running a production line I'd go for the correct tool, but for the average workshop this seems more than adequate..

 

Andy

I'm Andy H and I approved this message.

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Andy,

 

I'm sure you're right. I should have thought to point out what you have just said. For the cost of a VFD you can burn up several grinders, and that would take years at that.

 

Speaking of burning up:

 

My shop runs on 480 Volts (three phase of course). Recently the roof leaked and filled a big band saw I have with water. I was very careful checking everything out before I turned it on, but I did turn it on. It shut of the power to three buildings on campus. :embarrassed_smile: 480 volts @ 250 amps. No breakers tripped, but the sub station behind the shop did. KABLOOEY!!!!

 

I hate electricity!

 

 

At Your Service,

Clydesdave

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Hi,

 

most of the cheap bench grinders do not use a motor of the brush type. They use an induction motor instead.

Information can be found on the internet to understand how this works ; thik link explains most of the related principles.

However, the rotation speed of these units is clearly related (more or less proportional) to the frequency of the AC input. This means you will not change the speed by using resistors, since they only reduce the supplied voltage.

 

All the best,

Antonio

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Andy,

 

My shop runs on 480 Volts (three phase of course). Recently the roof leaked and filled a big band saw I have with water. I was very careful checking everything out before I turned it on, but I did turn it on. It shut of the power to three buildings on campus. :embarrassed_smile: 480 volts @ 250 amps. No breakers tripped, but the sub station behind the shop did. KABLOOEY!!!!

 

I hate electricity!

 

Ouch! I can imagine the "Who me?" looks I would have made!

 

I'm Andy H and I approved this message.

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I don't know about the conversion. I use my drill press for just about everything. It has 4 speeds via moving the drive belt to different size pulleys. It works well for buffing.

 

Regards,

 

danny

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Danny, I've done that too, but sometimes I find it easier to grip a workpiece when the wheel is rotating in the vertical position. I also have a variable speed lapidary wheel that can be set at any angle between horizontal and vertical, which is very nice for some uses.

I'm Andy H and I approved this message.

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Well, the OP didn't PM me, so I don't know why he wanted to slow it down. My suspicion was that it was to easy to burn the things he was grinding (i.e., get them too hot). One way to fix this is to get rid of the absolutely crummy grinding wheels they put on the cheap grinders and buy some better, more friable ones. This can make a huge difference. The other obvious method is to put smaller diameter wheels on to reduce the surface speed, but this of course can reduce the cutting speed.

 

The best approach, IMHO, is to buy a quality industrial Baldor grinder that turns around 1500 rpm. You only cry once when you buy it and it will probably last you the rest of your life. I'm still using one that was my grandfather's and probably dates from the 40's if not earlier.

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I want it slower so that I can a] polish pens, and b] grind nibs.

Fool: One who subverts convention or orthodoxy or varies from social conformity in order to reveal spiritual or moral truth.

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