My bench grinder came with two wheels. One is gray and the other white, but both are labeled “60 grit – medium – aluminum oxide.”
I don’t get it–how can the same compound be two different colors? And shouldn’t one be coarser than the other?
What kind of wheels are less apt to overheat the metal being ground?
Janet
Edited 12/28/2002 11:16:36 PM ET by DWREAD
Replies
Leonard Lee's book, the Complete Guide to Sharpening, available from Taunton Press, has a very thorough explanation of grinding wheels. Besides the grit size, two other important variables are the hardness of the bond, which affects how fast the wheel wears, and the density, or the amount of empty space built into the structure of the wheel. The white stone is probably both softer and more open than the gray one, and is less likely to overheat your tools.
Edited 12/29/2002 12:26:00 AM ET by Uncle Dunc
I did read that section in Lee's book before posting my question, but couldn't use his information because my wheels aren't coded. The only information is what I mentioned. The two wheels are identical except for color. They even weigh the same.
Somebody wrote, "As usual, we recommend replacing the supplied wheels with wheels made of"--but of course I can't remember either the composition they recommended or who wrote it.
Janet
Janet
"With wheels of aluminum oxide". The white one is softer than the gray and will wear quicker. On the other hand it will have less tendency to overheat the metal. Use the white to sharpen and the gray for general grinding.
If you want to go to a higher grit white, that is your option.
sarge..jt
I can understand being suspicious of the unmarked wheels. Maybe you'd be happier converting them to paperweights and getting new ones. With the information from Lee's book you should be able to order exactly what you want, and they're not that expensive. My 3 year old MSC ( http://www.mscdirect.com ) catalog shows Norton 6" x 1/2" aluminum oxide wheels for less than $10. There are lots of sources. A Google search for
"bench grinder" "aluminum oxide"
returned more than 500 hits.
BTW, what kind of grinder is it? If you got the new Delta variable speed, you got a 60 grit white alum oxide. On the other side is a 60 grit silicon carbide in gray. Your gray is then mis-labeled. I have never seen the alum ox in anything other than white. Could be, but I doubt it...
sarge..jt
It's a Delta GR250, which is the 23-655 relabeled to identify it as their low-end Shopmaster line. Both of my wheels have the same manufacturing code, so you must be right about the grey being mislabeled. Thanks!
Janet
I can't comment about what wheels are shipped with any grinder, but there are lots of gray aluminum oxide grinding wheels. It would surprise me if an economy grinder came with a SiC wheel because they cost quite a bit more than AlO. I would also expect a SiC wheel of the same size to be heavier and the individual abrasive grains to be noticeably shinier. Another distinguishing characteristic is that the SiC wheel will grind carbide a lot better than AlO, all else being equal.
The grey wheel doesn't look shinier. Without more information, I would be better off buying new wheels. According to Leonard Lee, "The stones that come with the standard bench grinder can be put to better use as patio stones than for grinding chisles and plane blades"! He recommends an A80-H8V (aluminum oxide, 80-grit, soft grade, open structure, vitrified) as "the best all-purpose stone for dry grinding in a woodworking shop."
I don't need more patio stones, but could these mystery stones be used for wet grinding? Lee commented that "it is nearly impossible to get hand-powered wet grinders any more," which got me wondering how hard it would be to make one from scratch.
Janet
U D
I know the new Delta has a grey silicon carbide 60 grit and an alum oxide 60 grit along with variable speed. I agree that an economy grinder would probaly not have the more expensive white stone. I have never seen the alum oxide other than white. Then again, I haven't paid temendous attention to that aspect either as that issue was settled long ago for me. I will check it out. Looks like I need to update a tad.
Thanks for the info and have a good day...
sarge..jt
Grinding wheels could be a moot point for me, too. After reading about sharpening using plate glass and sandpaper, I ordered fancy-schmancy sandpaper: 3M Microfinishing film in five different grits.
In hindsight it wasn't a practical purchase, as I have no planes--I don't do fine woodworking; mainly home repair, rigging for craftwork, and learning basic techniques. The prospect of learning the "scary sharp" method was just too enticing....
Janet
Edited 12/30/2002 3:54:39 PM ET by DWREAD
Is it dangerous to grind on the side of the wheel? The literature that came with the grinder warned not to try it.
Veritas has a sharpening jig that uses the side of the wheel. I ordered it anyway, on the assumptions that (a) the process isn't inherently dangerous as long as the wheel is in good condition, and (b) the warnings were insurance against product liability lawsuits.
What kind of safety equipment do you wear when using a grinder?
Janet
Janet
Grinding on the side of a wheel can weaken the stone for these reasons:
1 a lot of wear can undercut the outer circumference of the stone
2 lateral pressure also weakens it ,making it liable to crack.
However I still sharpen skew chisels on the side but very gently and toss out the stone if it shows signs of wear . I would not recommend ever dressing the side
As for protection, goggles (a dust mask if you are exposed to dry silica)and remember you'll need body armour or a body bag if the stone bursts on a high speed wheel !
Jako.
When you start the grinder, stand out of the plane of the wheel until it gets up to speed, and avoid standing in line with it whenever you can.
The grinder is used to get any nicks, etc. removed from the edge. The real edge comes after from methods as you mentioned. I use Japanese water stones. They're messy, but I loved to play in the mud when I was a kid. <G> Excellent results from them. The other methods work great also.
Have fun playing and learning....
sarge..jt
Janet
Ditto Uncle Dunc on his explanation. The white stone is softer. Might add most grinders run at too high a rpm. Baldor and now Delta (possibly others) offer a slower speed grinder. The problem with high speed is, it's very easy to overheat the metal in what you're sharpening. Once you do, it will never yeild a fine edge as the metal has lost it's temper and prone to be brittle.
Evening...
sarge..jt
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