I agree with Harold in all respects save one. If you have a badly worn
bench grinder wheel and you want to get it flat again, a star dresser will
do the job much faster than anything else. That's why I keep one in my shop.

Grant

Harold & Susan Vordos wrote:

"Brian Lawson" wrote in message
...

Hey Harold,

I kinda missed where this thread was going. Are you advocating use of
a stick for touch-up after truing with the diamond on my surface
grinder and on my Black Diamond drill sharpener?



Hey Brian,
No, never for machine type grinding, that defeats the purpose of the
diamond. Conditions on a precision machine are far different from offhand
grinding, though. I'm not certain when diamonds became the dressing tool
of choice, but there was a time when precision grinders were dressed with
star dressers. In today's demanding world of precision and fine finishes,
that wouldn't fly.

The point of my post is that dressing wheels with a star dresser is
wasteful, and achieving respectable results can be difficult. A diamond
works very well for truing the wheel, but the superior finish it leaves on
the wheel creates a couple problems that are not in the best interest of
offhand grinding, especially tool bits. Because of the slick nature of a
diamond finished wheel, it takes considerable more pressure to get the wheel
to cut. It also cuts one hell of a lot hotter. Anyone that knows
enough to run a cutter grinder knows that wheels are hand dressed when
sharpening end mills. That prevents over heating of the cut, and the wheel
demands dressing often to maintain the cool cutting condition. The
same principle applies to offhand grinding. By using a dressing stick,
the wheel is slightly roughened, which lowers cutting pressure tremendously,
and heating as well. That is not to say that diamonds don't have a place
on cutter grinders, or on pedestal grinders, but you have to know when to
use one, and when not to. There's nothing wrong with using a diamond to
get a wheel running true, but it should be slightly roughed up with a
dressing stick before using it to grind offhand. If that's not right, then
the shop where I was trained did it wrong for years.


You know, I've got some dressing sticks I picked up with wheel stones
at auctions. At least one white and a few black, but never used any
of them. Sounds like I should learn. Does the stick "colour" mean
anything we should know about, say relative to colour of the wheels?


Fine grained dressing sticks that are white are primarily intended for
dressing diamond wheels. Yeah, I know, that sounds nuts, but diamond wheels
get loaded with particles and get glazed such that they start not cutting
well. By running a fine stone on the diamond, the crud is removed and the
wheel surface restored. You're not really doing anything to the diamond,
and if you do, you're doing it wrong. The dressing operation should do no
more than clean the wheel, and the diamond tends to remove material from the
dressing stick, as it should be. You don't want to remove the matrix bonding
the diamond for obvious reasons. Dressing diamond wheels should not be a
prolonged operation, one should stop the moment the wheel is cleaned.

The dressing stick I used for years for that purpose was black in color, but
a friend recently gave me a new one, which is white. The black one is no
doubt silicon carbide, the white one aluminum oxide. Both will clean a
diamond wheel, and I have no idea why they are made from both abrasives.
In the scheme of things, the aluminum oxide one would certainly be softer,
kinder to diamonds, but the hardness difference between diamonds and silicon
carbide is so great I'm not convinced it makes a significant difference.

If you have in your collection of dressing sticks one that is very coarse,
made of shiny black bits of abrasive, it is most likely a silicon carbide
stick made for dressing aluminum oxide grinding wheels. There would be no
harm in trying it on a grinding wheel on your pedestal grinder, which is
where I highly recommend these items be used. If it is a dressing stick,
the wheel is readily abraded. I suggest you not use a white one on an
aluminum oxide wheel, use only a black one.

It was common practice for us to use dressing sticks to relieve the sides of
wheels when we had face work to do. Even on precision grinders, face work
is generally done with hand dressed wheels, and for the same reasons,
keeping heat down. It was not uncommon to get heat checking on faces of
heat treated tool steels otherwise, so how the wheel was dressed was rather
critical. Face grinding keeps a lot more of the wheel in contact, so more
heat is generated. The rapid heating and subsequent quenching by coolant
was the source of heat checking. Hand dressing is almost mandatory for that
operation. That would be true if the side of the wheel was used to kiss
the face. If the wheel head is turned, a right angle is dressed on the
wheel and grinds both the cylinder and the face with the periphery of the
wheel. By grinding that way, the problem of heating is reduced to
manageable levels.

Hope this helps~

Take care.


You too!

Harold