Need advice on bench grinder wheels

[Lloyd-ss]

I respect the fact that selecting the correct grinding wheel is a lot more complex than grabbing one off the shelf at harbor freight.
I need something for roughing steel and stainless, something for shaping HSS tool blanks, sharpening HSS tools and drills, and maybe something for touching up brazed carbide. And hopefully wheels that don't break down too fast.

I need some new wheels and here is what I have, although I don't know EXACTLY what I have.

Wheel #1
8" 1725 rpm with a 1" white wheel with some gray/silver flecks in it. This is my favorite. Fine, dense grained. cuts very nice and doesn't build up too much heat. I use it for shaping the HHS tools and lots of general grinding. I like this wheel but don't know what it is.

Wheel #2
6" 3450 rpm with 1" with dark gray, coarse, open grained wheel. Cuts fast and rough but builds up heat fast. It is fair, I guess, for roughing. Don't know what it is but prbly don't want another one.

Wheel #3
6" 3450 rpm with 3/4" reddish brown fine, open grained. Cuts fast and fairly smooth, not too much heat. I used it a lot until i got the 8" white wheel which I like better on the 1725 rpm grinder.

Any advice would be appreciated.
Thanks, Lloyd

 

[Zeb]

If you need to sharpen carbide in light amounts, you can get a silicon carbide wheel instead of diamond($$). I use one for my gravers.

Your wheels are likely aluminum oxide, but hard to say without reading a label.

Those gray silver flecks on wheel #1 might be stainless or aluminum! Anything that will load on the wheel is a bad idea. They'll expand faster than the wheel when it gets hot and it will grenade. I saw someone do it once and it was an ear opener.

As soon as they start loading up, you can clean them up with a wheel dresser.

 

[Nerd1000]

White wheels are 'soft' (cool cutting, wears down quickly) aluminium oxide wheels for tool steel.or HSS.

Grey wheels are 'hard' (slower wear, more heat) aluminium oxide for deburring and general grinding.

Silicon carbide wheels are green, and their primary function is to spread abrasive grit all through your workshop. Usually you'll find that more material is removed from the wheel than the carbide you're grinding- this is intentional, carbide is almost as hard as the abrasive in the wheel so they have to wear down super fast to avoid the wheel becoming 'glazed' or blunt.

 

[Lloyd-ss]

Thanks for the info guys. It is kinda what I was figuring, but it is good to get some validation.

Zeb, I have never seen a wheel blow up, but I was guilty of filling one up with aluminum years ago. I have a 6" x 1" flap wheel that I keep on a grinder for aluminum and brass. The gray flecks in the white wheel appear to be distributed all the way through the wheel.

Nerd, That color coding you talk about seems to agree with the performance I am seeing. A totally worn out green wheel came on a used grinder I bought. I tried to use it but it was more like dumping sand on the floor.

I will dismount the wheels i have and see if the labels are still readable. Shouldn't have been so lazy, ha ha.
Lloyd

 

[Nerd1000]

As far as HSS grinding goes, I'd get a 46 grit white wheel for roughing and a 60 or 80 grit white wheel for finishing.

For shaping mild steel or stainless I think the ideal is probably a pink coloured wheel (usually a bit harder than a white wheel). You want an 'open' structure if you're grinding softer steels because it helps prevent loading up of the wheel.

There are some other special varieties. Ceramic wheels (usually blue) are supposed to be the bees knees for many jobs. I've never used one, but from what I've read they work by having frangible grains, when the grain gets blunt it tends to break in a way that forms a new sharp edge rather than being ripped out of the surface of the wheel. So they cut like a white wheel but wear down slower. I'm sure you pay for the extra performance.

 

[TonyM]

I use a CBN wheel for finishing. Expensive initially but worth it.

 

[clockworkcheval]

Some of my colleagues have switched to CBN for really all their grinding. Initially expensive but a very long service life. Fits on your regular bench top grinder. I adhere myself to the rule of thumb soft stones (white Alu oxide or green Silicium carbide) for hard materials and hard stones (grey/blue Alu oxide) for softer materials. For very sharp polish grinding and for putting a really sharp cutting edge on inserts I use an Extra Fine Diamond wheel on my Tormek slow (100 revs) wet grinder. Diamond is initially expensive but has an extremely long service life. Beware that diamond is harder then CBN of course, but it cannot withstand high temperatures in combination with carbon steel, so you don't want to use it on your regular high revs bench grinder.

 

[awake]

The key parameter that I look for is the hardness of the wheel. Counter-intuitively, the harder the steel, the softer the wheel needed to grind it. For HSS or tool steel, I look for an H or I. (The typical grinding wheel that comes on the typical bench grinder is something like an X in hardness.)

I would caution against relying solely on color. While there is a tendency among some manufacturers to make certain types of stones white or pink or so on, they don't have to - the color is added artificially.* I have bought stones of the same grade, grit, abrasive and so on, and have gotten grey, blue, and pink stones. All have worked equally well.

*The possible exception is silicone carbide wheels - I've only ever seen them in green. But then again, I have very limited experience with them, so perhaps they too come in different colors ...

 

[Lloyd-ss]

Thanks everyone!. I now remember reading much of this information years ago and realizing there was a lot more to it than I had realized. I picked up this 16" x 5/8" O.D. grinding wheel years ago at a liquidation store. For $10 it seemed too good to pass up, but here it sits, collecting dust. It still rings clear as a bell and has no chips on the edges.
It's probably a dumb idea, but I could install this on the 8" 1725 rpm grinder for finish work. Trying to decipher the codes, looks like an 80 grit, J hardness, F density, 2266 max rpm. (Definitely Maybe) It would be easy to try, and I am always game for weird experiments. If it worked, it would need to be dressed very seldom, and I really dislike that messy job.
Should I try it? Thoughts?
Lloyd

 

[clockworkcheval]

No harm in trying. I would definitively use a diamond dressing rod to sharpen it up on a regular basis. I'm not so sure about the finishing qualities of an 80 grit wheel; my Extra Fine Diamond wheel is 1200 grit.

 

[Nerd1000]

The key parameter that I look for is the hardness of the wheel. Counter-intuitively, the harder the steel, the softer the wheel needed to grind it. For HSS or tool steel, I look for an H or I. (The typical grinding wheel that comes on the typical bench grinder is something like an X in hardness.)

I would caution against relying solely on color. While there is a tendency among some manufacturers to make certain types of stones white or pink or so on, they don't have to - the color is added artificially.* I have bought stones of the same grade, grit, abrasive and so on, and have gotten grey, blue, and pink stones. All have worked equally well.

*The possible exception is silicone carbide wheels - I've only ever seen them in green. But then again, I have very limited experience with them, so perhaps they too come in different colors ...

SiC itself is a sort of grey colour (well at least the grit used for rock polishing is) so I think green wheels are artificially dyed as well.

You're quite right about the colour coding, it's really just a rule of thumb or guideline rather than a hard rule. That being said, all the white wheels I've come across have been 'soft' wheels of some sort. YMMV for the other colours.