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I recently went shopping to replace a cheap electric bench grinder that came with my property gave up the ghost. I noticed that all the bench grinders I looked at have 2 sharpening wheels.

I have also watched a video where the person replaced the a sharpening wheel with a polishing wheel.

Is there a particular reason I should know of as to why grinders have 2 grinding wheels rather then 1 grinding wheel and one polishing wheel? Is it a bad idea to [permanently] replace one of the grinding wheels?

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    Cheap coarse and fine grinding wheels are cheaper than polishing wheels.
    – Solar Mike
    Nov 29, 2020 at 9:58
  • got a cheap bench grinder here with one grinding wheel and one wet stone, the stone is on a worm drive so runs much slower than the wheel. I've also seen wire wheels on bench grinders.... there's so many options.
    – Jasen
    Nov 29, 2020 at 10:14
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    My bench grinder came with two grinding wheels. I purchased it twenty five years ago. Shortly after I replaced one with a wire wheel brush. Still working fine. Nov 29, 2020 at 13:42
  • I have 2 grinders 1 with a fine stone and a buffing/ polishing and a second larger with a corse stone and wire wheel like platinum goose mine are probably 30+ years old.
    – Ed Beal
    Nov 29, 2020 at 18:18

1 Answer 1

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Grinding wheels and buffing/polishing wheels you buy at the home improvement store have different max Surface Feet Per Minute needs. For buffing you generally need to get it up to 7500 SFPM otherwise you are going to be standing there all day long. Grinding wheels on the other hand generally require a lot slower speeds for many applications. For example if all you are doing is knocking a burr off a bolt you can use a coarse wheel at the highest speed no problem. If however you are using a fine grained grinding wheel to surface finish and add luster then you want to run it a lot slower. Wire wheeling (generally used for rust removal) is also safer at slower speeds as cheap wire wheels tend to throw wires at higher speeds.

Buffing and wire brushing also often requires the entire wheel to be exposed while it is dangerous to fully expose grinding wheels and stand in the plane of the wheel since if the wheel fragments at high speed you may be seriously injured.

I have noticed for example the trend at the Cheap Chinese Tool sellers to reduce inventory and stock of larger grinders in favor of smaller lower priced grinders. This is because the average casual tool user sees the RPM figure on the small grinder and thinks that's all that matters The CCT on the other hand is more worried about an idiot buying a big hefty motor and attaching a large abrasive wheel to it and having it frag him. These smaller grinders the CCT's sell are generally terribly slow and inefficient to use due to their safer and lower SFPM speeds but it's very difficult to exceed maximum safe SFPM speeds with them by the backyard mekanik crowd (who probably isn't even wearing safety glasses much less a face shield...)

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  • Newer wheels also have a shatter shield that helps stop the chunks at the top of the opening, a family friend co worker was seriously injured years back when someone ground aluminum and plugged the stone he was grinding steel and lost a testicle when the stone exploded, aluminum and brass need to be ground on a belt sander that won’t plug up and explode.
    – Ed Beal
    Nov 29, 2020 at 18:24
  • The correct silicon carbide grinding wheel can be used to safely grind aluminum. I would post the name and link of an example but that's not allowed here. Note that aluminum and other metal dust can be hazardous to breathe. Nov 29, 2020 at 18:41

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