Can I use a diamond wheel for cutting tile to sharpen my carbide toolbits?

diamond is the choice for sharpening carbide. If you're talking about brazed bits, keep in mind that the soft steel underneath EATS diamond. I have two wheels on my baldor, the green wheel is set to 8 degrees for ruffing and then the diamond wheel is set to 5 degrees for finish sharpen of the carbide.

Karl

The problem with using that type wheel is the limited surface available for doing your grinding, and is likely to yield poor results under normal circumstances. The typical diamond wheel that's applied for sharpening carbide lathe tools has the diamond on the side, in a broad area, usually about 3/4" wide.

Pay attention to the caution already offered on grinding steel. Diamond is destroyed by steel when applied at high speed----it actually is dissolved into the steel, cutting its useful life very short by dulling it until it doesn't cut well. Relieving it on an aluminum oxide wheel at a greater angle is the typical method of avoiding contact with a diamond wheel. Using a green wheel presents the same problems that diamond does---it, too, is soluble in steel. It's silicon carbide.

Unlike HSS, free hand grinding of carbide is not in your best interest. It's done best with an adjustable tool rest, so you can set the proper relief angles.

Harold

Harold,

I've gotten fair life out of the green wheel for ruffing brazed carbide bits on the the Baldor grinder. But I'm sure I'll have to replace it sometime. I've not seen aluminum oxide Baldor wheels, are they made? Will aluminum oxide cut carbide at all? I always thought carbide just bounces off.

I've always used the green wheel cause I don't know any better.

Karl

I've wanted to try that with my MK-101 wet tile cutter. I think side- loading a circular saw blade might be a problem. But they certainly make a smooth cut on the hardest stone, so I would think the carbide is a possibility.

I trust you're talking about the steel backed wheels, on which you use the face to grind, not the periphery. Yes, they're available, but are not cheap. If you intend to stay with the green wheels for carbide (I don't recommend it, and if you once try diamond you won't either) it's easy enough to go to an aluminum oxide wheel on a different spindle to grind the steel back to avoid contact. You'd do that with a diamond wheel, exactly the same way. That's what I've always done with diamond wheels, or when I had no choice but to use the green wheels.

Will aluminum

You've pretty much got it. Aluminum oxide is a lot softer than silicon carbide, but grinds steel far better because it *doesn't* dissolve into the steel the way silicon carbide does. Carbide is slowly ground by aluminum oxide, but at the expense of dulling the grain prematurely, much the same way steel does silicon carbide, but for different reasons.

In the scheme of things, it doesn't make a big difference, Karl. If you are the typical home shop type that occasionally sharpens some brazed carbide, the worst case scenario is you'll buy one extra wheel in your life time because you waste a little when you grind steel. Because green wheels are bonded softly, they are quite friable and break down quickly, which is the chief reason they work as well as they do when grinding carbide. Keep in mind that the silicon carbide is *not* any softer, just the bond. If they didn't break down, the dulling would quickly bring the grinding to a halt. When you grind on steel, although it's quite soft, the grains dull very quickly and are shed, exposing new, sharp grains. That's where you experience the loss. As I said, for casual use, no big deal. The only real issue would be a health one, which is silicosis. Breathing the dust is not a good idea, and you make plenty of it when you shed the wheel.

Harold

I have one of those MK saws sure beats lugging in a heavy wet saw. Not long ago I customized it to cut 16" tile , was just .5-.7" short. It took awhile to figure out how to do it and at the same time bitchen at the designer. Harold uses diamond , all I know is that I won't cut steel with any of my blades. I find the oldest beat up one to customize trowels (seems to be about the only thing that will go through them) cause they go down hill fast when I go back to tile.

I had to laugh at myself the time I made a segmented blade out of one with another ! Still have that one. Never did try sharpening metal cutting tools with them cause even rebar screws them up around me. Matter of fact the price at least doubles if I see metal sparks while cutting concrete just to calm me down when I buy new ones. My father-in-law thinks it's cool to cut steel with them and I just cringe and shut up.

The fact that diamond dissolves into steel, destroying the diamond, is well known, and published in literature from Norton. Research on the subject was conducted back in the early 50's, as I recall. Running diamond on steel at elevated temperature, such as high speed grinding, is death on diamonds. You're smart to avoid doing so.

And now you know why!

Harold

You _can_ cut steel with diamond. You just have to run it so slow that it doesn't heat up. The down side of this is that it's slow :-(

Mark Rand RTFM

Didn't I say that?

Harold

I think we need to think about this a little.

Diamond cutting tools are steel based and cut steel HSS and carbide drills and mills. Perhaps there is transference, but not all that much ?

Mart>

The cutting part of diamond tools is diamond (natural industrial diamond or vapor-deposited diamond coatings, or, in a couple of rare cases, vapor-deposited diamond stripped from a substrate and diced into thin braze-in tips), or diamond bonded in a press-and-sinter operation with one of several binders (PCD tips). There is no steel involved in the actual cutting tip.

As someone said, diamond combines chemically with steel or iron much quicker at high temperatures. It's a very expensive way to carburize a piece of steel.

It works Ok for cool lapping, badly for turning or milling, and it's a big loser in grinding. Still, it has its uses for cutting ferrous metals. You just have to be aware that you're in for an expensive proposition because of the chemical action.

A couple of years ago I talked to a scientist at GE materials and I was surprised to hear him say that cubic boron nitride (CBN, or PCBN) also combines with steel at high temperatures, but at a much slower rate than diamond. Chemistry is one of my weak areas so I can't comment but to pass on what I read or hear.

Anyway, CBN lives as a tool material because of the problem of diamond combining with ferrous metals in common metalcutting operations, simply adding to the carbon content of the metal being cut.

-- Ed Huntress

They may do that, but are they recommended for the application? Dunno. I've never used diamond turning or milling tools. If so, do they recommend specific speeds, to keep the temperature down? That's the critical point.

I'm not convinced I'm the right person to answer the degree of transfer, but for diamonds that rely on sharp corners to do their work, it takes very little to change them appreciably. Iron has an affinity for carbon, and it isn't proud where it gets it. Up to the point of saturation, so long as the temperature permits transfer, it will absorb it. That tells me that prolonged contact at high temperature, iron could literally absorb a complete diamond.

It's not a heat thing alone, nor is it an iron thing. Diamonds will withstand soldering (re-tipping prongs, for example) with no ill affects, and they can withstand a constant dressing of aluminum oxide or silicon carbide wheels, even large ones such as are found on centerless grinders. They are often 24" in diameter and 8" or more wide. Heat isn't a problem, but combined with iron, it quickly becomes one. That's about the extent of what I know, and from experience, I know that contacting diamond wheels with iron (steel) is a mistake. The typical diamond wheel feels as if it's been greased once steel has been applied. Sorry I'm not more help.

Harold

So you can't grind HSS on a green wheel?

Not with great success. The green wheel will break down very rapidly due to dulling of the abrasive by dissolution. Being softly bonded, it readily sloughs off to expose new bits of abrasive, which, in turn, dull quickly. By contrast, you can use an aluminum oxide wheel that is softer, but bonded much harder, and grind without any loss of wheel because the aluminum oxide doesn't dissolve into the steel. It stays sharp much longer, so it has no need to slough off, thus a harder bonded wheel. That's the reason tool and cutter grinder wheels (where cutting tools are made from HSS) are made from aluminum oxide instead of silicon carbide.

It pays to match the grinding media to the work at hand. You not only get a better quality job, but the wheels hold up much better and work faster.

Harold

I would like some input on Drill-Doctor using a diamond wheel to sharpen

HSS drill bits. It works OK.

I can only assume that the wheel runs under a critical surface speed to avoid the temperature at which the diamond begins to dissolve.

I'm not familiar with the Drill Doctor, although I have heard of it. Personally, unless I had carbide drills, such as masonry drills, to sharpen, I'd opt for a better grinder, one that gets the job done in a timely fashion. I'd also learn the art of hand grinding drills. That can and will serve you for ever. I practice what I preach. I can hand sharpen flat bottom and split point drills, along with conventional points, and I own a Darex.

Harold

Remember the diamond is mounted on a steel or is it Nickel - hum - ring. The ring is a heat conductor to the main shaft that is cooled. The diamond is the most efficient conductor of heat - Sapphire is next. So the diamond that gets hot is rapidly cooled as it is turned at very high speed. In general, cooling is best at all times, but there hasn't been a scram issue on replacements for the unit from what I can tell it is still for sale. I have one, and have ground both HSS and simple steel (if there is one) and even ground a carbide tip drill. My spare wheel bought at the time of sale is still in the machinist chest where it was saved. I don't use it often, I use it as a pre-grinder or drill saver. Releaf behind the grinding edge is not relieved. I save the drill - might split grind it and then hand grind the fine touches as needed.

The drill Dr. isn't perfect but gives me a well pointed (centered and maybe split) so my grinder time is for touch up not heavy grinding a chip.

Martin

Diamond is typically grinding and sawing. Sapphire is and Diamond I believe used in exotic sharp edge cutting of plastics and glass. Typically both fracture under load if not supported.

Since the diamond is best in conduction - your hand on the far side of a thin diamond window would feel almost all of the heat on the other side - so when the tool tip gets hot, it conducts to the base metal - steel and flows off - cooling the diamond.

Continuous heat addition (at one spot ) (as with a flame or arc) would, but a turning tool and the conduction prevents this. Also the typical use involves a flood of water based coolant.

Martin

tool tip gets hot,

I'm not sure what you're saying here, Martin, but diamond turning and milling cutters are not used on ferrous metals except in very rare situations. They just don't last, for the reasons Howard has explained.

In production, diamond is use primarily on high-silicon aluminum. Other uses include composites, plastics, glass, and other non-ferrous metals.

The development that made polycrystalline synthetic diamond a near-necessity in production was the use of very high-silicon (hypereutectic) aluminum casting alloys in automotive applications. Another one of the early users was Mercury Marine, who used it for machining their hypereutectic outboard motor blocks. OMC soon followed suit.

-- Ed Huntress