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 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
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.
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
"Karl Townsend" wrote
in message news:ulwOd.4379$ firstname.lastname@example.org...
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.
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.
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!
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
Harold and Susan Vordos wrote:
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
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
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.
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
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.
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.
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
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
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
from what I can tell it is still for sale. I have one, and have ground both HSS
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
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
hand grind the fine touches as needed.
The drill Dr. isn't perfect but gives me a well pointed (centered and maybe
my grinder time is for touch up not heavy grinding a chip.
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
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
tool and the conduction prevents this. Also the typical use involves a flood
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.