Cal Meier wrote: "I receive advertisements talking about "low speed" grinders
for sharpening tools.  When I check, the
speed is commonly listed at roundly 1750 rpm.  What is a good "low speed" to
sharpen at using an 8" wheel.  Any thoughts or strong opinions would be
appreciated."


One of my main sharpening tools is a 4-1/2" handcranked wheel, geared up by a
power of ten, medium-coarse with a pretty tight bond. I believe my usual
cranking speed gives the wheel an RPM of 500 to 800 RPM, which translates into
225 to 450 RPM for an 8" wheel. At the upper end of this range there is real
danger of burning the edge if I maintain the speed; at the lower end I am pretty
safe, even if I don't pay much attention to cooling the edge with water.
I don't know how much this pragmatic result would be altered by using lightly-
bonded sharper white or pink wheels, which can take higher RPM.

For grinding edges, 1750 RPM is ridiculously high; since you must cool the steel
so often, I think you actually spend more elapsed time to grind an edge. I've
known people who tried using a power cord with a rheostat with ordinary bench
grinders to bring down the RPM, and sometimes it works but sometimes you just
get "too fast" going suddenly to "stopped" as you turn the rheostat down.
On the other hand I wonder about the speed of the Tormek, which seems way too
slow, considering that it is running in a water bath. The T-4, at 8" diameter,
is running at only 120 RPM; the T8, at 10" and 90 RPM, must have an even smaller
surface speed in feet per second (which, of course, is the real point at issue).
Maybe they expect the Tormek to be used right down to the edge, not for the
primary bevel. I've never used a Tormek, so I hesitate to judge it. But I sure
don't plan to plonk down seven hundred bucks for a badly-thought-through wheel
that needs a different jig for every tool.
What tempts me is variable-speed grinders; but I've never priced them. I have a
Makita horizontal wheel, which I'm devoted to, but that is a motorized hone (for
use on secondary bevels and backs), not a grinding wheel.
Well, there's the thoughts and strong opinions. Probably someone else has said
it all by now; I'm trying to catch up on my incoming queue.

Tom Conroy
Berkeley