The Home Machinist!

I've been noticing some remarkable prices on "diamond" cup wheels, well under $10 from some sources. They seem to be intended for angle grinders and/or concrete finishing.

I wondered if one of these might be a useful way to reshape my collection of chipped or broken brazed-carbide tool bits. A coarse diamond wheel might remove carbide more efficiently than a green wheel.

In the pictures, the hubs of some of the cheap diamond wheels look like stamped steel. I'm guessing, given their price and intended purpose, that any roundness, flatness, and concentricity are purely incidental.

Which leads me to the question... how *do* you true up a diamond wheel?

I guess you would figure out a way to mount the wheel with the diamond part running true (if possible) and then machine the mounting surfaces. I can't think how to hold it but a dial indicator would allow you to get it in alignment.

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Don Young

It's possible you could enjoy some success if you have a tool & cutter grinder, but for brazed carbide bits, you're far better served to use a type D6 resinoid bonded diamond wheel. While a cup wheel can remove the material, it isn't well suited for lathe tools, where you (generally) desire straight, flat surfaces.

If you're not familiar with the old wheel designations, this is a wheel that uses a portion of the side for the diamond layer. They are typically 6" in diameter, with a layer (1/16" or 1/8" thick) of diamond on the side, 3/4" broad. The wheel is recessed, leaving only the diamond layer for contact. Such wheels are used on a grinder that has circulating coolant, and, yes, they exceed, by a wide margin, the performance of green silicon carbide wheels.

Here's a picture of a typical wheel and how it's applied. Note that the table is adjustable for grinding desired relief angles.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Those diamond wheels meant for concrete finishers would be totally unsuitable for grinding carbide bits. The diamonds are course and widely spaced. They would beat a bit to death. As far as truing them, there is only one layer of diamonds on them that are electroplated onto a metal surface. They work great for their intended purpose but they would be a disaster for trying to sharpen a carbide bit. there is a reason that a good diamond wheels cost so much. They run true and there is a thick layer of diamonds on the face of the wheel. You can buy cheep diamond wheels. (check lapidary supplies) but they have just a single layer of diamonds and wear away pretty fast.

So, how long would it take to grind 1/4" off a broken carbide bit to get to where I can actually worry about sharpening it? How long will a proper diamond wheel last, doing that sort of thing?

not sure how to put it perspective. my baldor carbide grinder has gone thru 2 diamond wheels in about ten years and 20 of the green wheels and yes i run them wet and don't use them for hogging out cutters.

A great deal depends on the wheel that is chosen. I say that because there are variables that have a profound affect on the expected life of a wheel. One of the variables is the percentage of diamond in the coating, and the other is the depth of the coating. How the wheel is bonded can play a huge role, too, but you are best served using a resinoid wheel for sharpening brazed carbide. I recommend one not choose a metal bonded wheel, as they tend to chip fine edges. I also recommend a wheel in the 200/220 grit range, assuming one would own just one wheel. That is an excellent compromise for both roughing and finishing.

In my one man (commercial) shop, I ran with the same wheel for all 16 years I was in business. The wheel in question was nearing the end of its useful life. It was a 100% concentration wheel, with a 1/8" depth of diamond. In the overall picture, such a wheel is most likely the best investment. It would be safe to say that the normal home shop type would be highly unlikely to consume one of even 1/16" depth in their lifetime.

Wheels that cost in the vicinity of $600 in the late 50's are now commonly available for less than $200. They are an absolute bargain, considering the work they are capable of producing for the cost. They are also grossly superior to the green silicon carbide wheels. They aren't hard enough to cut carbide cleanly, so the resulting edge is never as good. In general, tool life is diminished because of premature edge failure (due to the rough finish) and tend to consume more of the tool in the grinding process. Worst of all, silicon carbide wheels are very destructive of lung tissue. My advice is to avoid their use unless you have no alternatives.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.