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Old 06-23-16, 09:33 AM   #1
noglider 
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bench grinder

I have a bench grinder and wore out one of the wheels. I looked at various grinding wheels on Amazon, and there is a lot of variety. How do I choose? I use it for grinding down metal while working on bikes. There are various materials and various grit levels.
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Old 06-23-16, 09:44 AM   #2
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largely like 'sandpaper' it is all about grit courseness..

carborundum.. to preserve the temper on steels dont let it get too hot. water dip your work regularly.

never put Aluminum against a grinding wheel, use a File.

worn out wheel can be grit size matched if you use a walk in shop to buy it.

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Old 06-23-16, 10:07 AM   #3
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As Bob, I use carborundum, for general purpose grinding. One "fine" wheel, one medium. Course is useless except for shaping large items.

If I had to choose one, I'd go with fine.

Grab a wheel dresser, too, if you don't already own one; the grinding wheel will last longer and be more useful if you periodically true it.
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Old 06-23-16, 10:09 AM   #4
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I did use the grinder on aluminum. Please tell me why that's bad.
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Old 06-23-16, 10:43 AM   #5
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Because the aluminum will 'junk up' the wheel, ruining it's grinding ability. Also, aluminum tends to 'spread' more than grind-kinda like soft butter. A fast grinding wheel will actually melt the surface a bit, which does things like ruining the temper of the alloy, weakening it. Also, aluminum dust is explosive, and aluminum can actually burn if heated to high temperature (as will magnesium). A file at a hardness of 60Rc should be all you need, even for 7075.
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Old 06-23-16, 11:31 AM   #6
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Use a file made for aluminium. If you have to use a file made for steel, load it up with chalk, like sidewalk or blackboard chalk. This will help it from clogging too quickly.
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Old 06-23-16, 11:35 AM   #7
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I use a cheap disc/belt grinder for shaping aluminum, the abrasive paper seems to shed the aluminum and not load up like a wheel does. Or a Dremel tool with a sanding drum for small inside corners.
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Old 06-23-16, 11:40 AM   #8
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# 1) Aluminum can be returned at High speed as a Projectile , causing wounds to the operator ..


A Nicholson Vixen file has widely spaced teeth to make aluminum Chips easy to remove .

It was of course developed for the aircraft manufacturing business , (and Aluminum Boats)
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Old 06-23-16, 12:11 PM   #9
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# 1) Aluminum can be returned at High speed as a Projectile , causing wounds to the operator ..
Gloves, face shield and a leather shop apron work for me.
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Old 06-23-16, 12:12 PM   #10
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Aluminum, also, expands more than steel, so the aluminum that gets embedded in the grinding wheel can cause the wheel to crack and ...you guessed it: asplode!
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Old 06-23-16, 12:39 PM   #11
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Maybe a Bunker would be better .. when the grinding wheel comes apart .

my Father had a career as a Machinist (shipyard, weapons Making) from his return from WW2
until I was Out of the house to go into the Navy during Viet Nam war time,
when he retired .... and had a Home machine shop in the Garage..
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Old 06-23-16, 12:46 PM   #12
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Because the aluminum will 'junk up' the wheel, ruining it's grinding ability. Also, aluminum tends to 'spread' more than grind-kinda like soft butter. A fast grinding wheel will actually melt the surface a bit, which does things like ruining the temper of the alloy, weakening it. Also, aluminum dust is explosive, and aluminum can actually burn if heated to high temperature (as will magnesium). A file at a hardness of 60Rc should be all you need, even for 7075.
So in other words, noglider is probably already dead, exploded from alu dust, and then smothered in a tidal wave of molten alu
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Old 06-23-16, 01:12 PM   #13
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I appreciate the warnings. I will now read up on proper procedures. I injured my eye when I was 21 by using a grindstone without goggles. I blame the boss for not teaching us. I'm lucky the injury wasn't permanent.

I ground down the wheel making a two-part shim. The LBS split a seatpost to make the shim for me but the OD was too high. I clamped the two sides to the seatpost with zip ties and turned it over my grindstone. The result is excellent, especially considering I had never done anything like that.

Now I know I did something dangerous, and I won't do that again.
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Old 06-23-16, 01:17 PM   #14
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FWIW, any place I've ever worked, when they needed to grind aluminum, they either used a Scotchbrite wheel (for minor breaking of edges), or else a belt or disc grinder. There would often be a 2-wheel grinder with one side for 'mild' steel, and the other side for carbide, with an explicit sign saying "do NOT grind aluminum on this grinder"
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Old 06-23-16, 01:54 PM   #15
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The most common wheels for bench grinders are aluminum oxide 60 to 80 grit, which are grey colored and probably what your grinder came with originally. Green silicon carbide wheels can be faster, but are slightly more brittle, so not the best choice for people without a steady rest and decent hand skill.

The reason you don't grind aluminum is that it melts and fuses in to the wheel clogging it, which makes it run hotter making the entire process progressively worse. Steel can also load a wheel, if you don't use good technique, which is to let the grinder do it's job so the hot material leaves as sparks.

If you want to do good work, buy yourself a diamond dresser, and use it often to keep the wheel open and square, so it runs cooler, and will give you flat ground edges.
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Old 06-23-16, 02:21 PM   #16
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If you want to do good work, buy yourself a diamond dresser, and use it often to keep the wheel open and square, so it runs cooler, and will give you flat ground edges.
That's good advice. It's not just that the face of the wheel is flat and square. The dresser, also, cleans away the embedded metal, and presents a fresh cutting face to the work, making grinding faster, cooler, and more fun.

Dress early! Dress often!
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Old 06-23-16, 02:22 PM   #17
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If you want to do good work, buy yourself a diamond dresser, and use it often to keep the wheel open and square, so it runs cooler, and will give you flat ground edges.
Wow, you brought back a memory. In winter of 1980/1981, I worked in a bike shop in Cambridge, Massachusetts, and we would sharpen ice skates. We used some kind of diamond point to dress the wheel and leave it with a rounded shape. That shape is right for skates because we made a round groove in the skates' blades.

I'll get the dresser along with my new wheel.

I'm learning a lot here!
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Old 06-23-16, 04:52 PM   #18
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That's good advice. It's not just that the face of the wheel is flat and square. The dresser, also, cleans away the embedded metal, and presents a fresh cutting face to the work, making grinding faster, cooler, and more fun.
!
What I meant when I said it keeps the wheel open and square.

Here's a trick for using a diamond dresser on a bench wheel. Buy a small hose clamp or shaft collar to fit the shank of the dresser. Set the tool rest at or slightly above the centerline, and pull it back from the face about 1/2". Place the collar on the dresser and use it as a gauge to set depth and run It along the tool rest to make your passes. Tap the rest in a hair for each pass, until the wheel is clean and open.

BTW - this method only produces good results if you're no a klutz and never swung the tool rest into the moving wheel, leaving a notch.

Also, typically grinding wheels are only good until worn to 2/3rds of the original diameter. Smaller wheels have slower surface speeds and will not grind as effectively.
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Old 06-23-16, 05:41 PM   #19
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I use an aluminum oxide wheel on one side and a fine wire wheel on the other. I get more use out of the wire wheel.

I get much more use out of an old Delta 4" belt 6" disk sander. it has a table and miter gauge for precise shaping. Unfortunately, it's worn out and they don't make them anymore.

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Old 06-23-16, 07:54 PM   #20
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the aluminum will 'junk up' the wheel, ruining it's grinding ability.
As will brass. And there is a real risk that such a clogged wheel will suffer thermal stress, which can cause it to fracture, sending shrapnel out at high speed. A wheel dresser can remove the clogged surface are expose a fresh surface:

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Old 06-23-16, 10:19 PM   #21
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I'm learning a lot here!
Me too. I'm guilty of having used my bench grinder on aluminum parts, but had no idea it could be dangerous! Just knew that grinding discs and bits got a lot less useful once loaded up with aluminum filings.
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Old 06-23-16, 10:30 PM   #22
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FWIW - it is OK to do a limited amount of grinding of aluminum or brass. It's less than ideal but manageable. The key is to let the grit do it's job with light feeds and keeping the work cool. As with steel, loaded wheels will run hotter, so keep the wheel open (dressed), and the work cool.

When finished, redress the wheel so it'll be ready for it's usual job in steel.
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Old 06-24-16, 07:27 AM   #23
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For deburring edges, cleaning off rust or oxidization, or even shaping aluminum to some extent, you can't beat a 'convolute' wheel. I have a fine grinding wheel and a 3M convolute wheel on my grinder at all times. It yields a consistent brushed finish on even hard metals like stainless steel as well.
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Old 06-24-16, 07:52 AM   #24
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On the topic of bench grinders...I've always felt that using it in the proxcimity of where I store and work on my bikes is probably not the wisest thing to do. All those metal flakes getting on the drivetrain, maybe working into wheel bearings... Makes me shudder. I still do it, but at least I try to take precautions to limit it.

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Old 06-24-16, 08:07 AM   #25
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Another thought....depending on the state of the wheel....getting a dresser may be all you need to make it usable again.
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