Hello All. I have one of the 129.99 on sale H/F dual wheel tool grinders
with green wheels for sharpening carbide lathe tooling. I have read on this
forum a number of times that these wheels nor diamond wheels should be used
for sharpening tool steel tooling. I normally use carbide tooling but am
thinking of switching to tool steel as it can be ground so much sharper and
almost all of my cutting is wood or phenolics which needs a sharp edge. Any
way, the question is, what would be the best stones to put onto this grinder
to form and sharpen tool steel?
The favorite of many people is Norton's white wheels, which are soft-bonded
aluminum oxide. 60 grit is preferred because it cuts much cooler than finer
grits and you're only supposed to use a wheel for shaping, anyway. Most of
us go farther than that, grinding lathe tools almost to completion and only
taking a few finishing passes on a hand stone.
If you do woodwork and you want something that is also semi-safe for
rough-grinding your plane irons and chisels, the white wheel is the way to
go. But high-speed steel -- the real stuff, not the Chinese "M50
equivalent" -- is tempered at 1050 deg. F or higher and actually can be
ground until it glows very dull red. Try that with your plane irons and
they'll be ruined forever, of course. But don't worry if you draw some
color -- straw, peacock or even dark blue -- with real HSS.
For that reason I use finer and harder wheels for grinding my lathe bits:
ordinary blue-gray Norton aluminum oxide. Stay away from Chinese-made Norton
wheels. They have a reputation for glazing badly. There are other good
brands; check around the Web to see what heavy users are using today. And
you really can grind HSS on your green wheels. Some people prefer them but
most stick to aluminum oxide because it leaves a better finish and it cuts
cooler, and it doesn't load or glaze as easily. Just don't use green wheels
on any other type of steel.
Yes! When HSS was used for production turning, machinists would grind the
stuff very aggressively. I don't hold HSS in my fingers. I either keep it in
the tool shank or I grab it with Vise Grips. The latter is *not* to be
recommended unless you're wearing full face protection and a bulletproof
vest. But it sure works. d8-)
I should have been more explicit on this point.
If you have the tool in some sort of holder [so you can hold onto
it] and have ground it until color starts to appear, its too hot
to dip, especially if you use cold tap water.
You don't want to let the tool get hot enough that it "hisses"
when you dip it in the water, and the water should be room temp.
If you have it in a holder of some sort where you can get it to
the point of color change, its too hot to dip. Its very [too]
easy to do this when you have a thin/fine edge for example a high
rake high relief tool. the heat conductivity of HSS is not good
and rapid local heat build-up while grinding is a problem.
One thing you can do in the home shop is to keep a spray bottle
[e.g. used 409 spray bottle] of water handy and mist the wheel
face from time to time. Not so much water that you make a big
mess, but enough to evaporate and keep things cool as you grind.
You can prevent [much of the] rust if you will add a little water
soluble water pump lube to the spray water -- 98 cents at pep
boys or wal mart.
Also if you want to get fancy, you can use fine grit wet-or-dry
finishing paper around a larger tool bit [to keep it flat] as a
lap or hone to put mirror finish on the tool if you would like.
I don't know how much good this does in normal use, but several
model makers I know swear this is the best way to sharpen tools
to machine plastics.
That probably protects it but that's an awfully slow way to grind tool bits.
If you're just redressing an edge I'm sure it's fine. But shaping a bit,
particularly in the initial grinding of a new blank, I'd think that would
take all afternoon.
Some years ago we had a lengthy discussion about this point and I did some
research, talking to engineers at Crucible, Carpenter, Fette, and one other
I can't remember and I got some funny reactions. They were mostly younger
than me and some of them didn't really know how to grind HSS. But I also
reached a couple of old-timers who were very emphatic that you can, and
often should, grind HSS aggressively to shape it. You do have to dress a
couple of thousanths off of the edge after you do that, cutting slowly,
because HSS will develop microcracks if you even look at it crosseyed and
you have to hone them out after shaping the tool. Also, as you say, the
extreme edge may get burned because of the poor thermal conductivity. But
that's only the very edge. You won't hurt the parent metal by going at it
pretty hard. This is very different from grinding other kinds of hardened
steel, which typically are tempered at 300 - 500 deg. F, and which will be
ruined if you overheat them.
One thing I noticed when I used to grind a fair amount of HSS is exactly the
point that John Martin made, which is that HSS grinds very slowly when you
do it gently -- in my experience, it simultaneously beats up your grinding
wheel, if you're using a soft or medium aluminum oxide wheel -- but that it
seems to hit a threshhold where it suddenly cuts fast. I reach for that
point where it just starts to cut fast when I'm shaping a tool bit.
HSS is a peculiar material with three different hardening mechanisms: a
conventional martensite conversion, which seems to play little or no role in
the performance of the cutting edge but which adds strength to the shank of
the cutter; solution hardening from the high-temperature dissolved
components of the alloy (tungsten, molybdenum, vanadium); and precipitation
hardening from carbides. The two-step tempering used for HSS produces a
conventional martensite, which can't stand any more heat than ordinary
hardened steels, and a solution- and precipitation-hardened phase that will
take very high temperatures without losing strength.
When you grind HSS slowly you're fighting a lot of carbides in a hard
matrix. It's hell on grinding wheels. When you heat it up the martensite
"matrix" softens, I think, and that's why there's a sweet spot at which it
grinds a lot easier. (That's my theory, anyway. It does seem to behave as if
that's the case.) When I say "matrix" it shouldn't be taken to mean that HSS
is just like cemented carbide tools. Most of the material in HSS is the
"cement," or the matrix, which in this case is the steel. The carbides make
up a low percentage of the overall material, unlike the case with carbide
tools. But it's enough to help harden the steel and to add a lot of wear
resistance, whether the tool is cutting steel or grooving the heck out of
your grinding wheel.
My conclusion from talking to experts and from my own experience is that you
should rough HSS very aggressively and then finish the tool gently. I won't
quibble with what you say about water-dipping if you keep the tool quite
cool in the finishing step, but I never dip it at any stage, having been
cautioned against it and also having seen some old photomicrographs of the
cracks that result in HSS from thermal shock.
Indeed, which is why I suggested roughing on a belt sander.
Hand grinding is requires application of the Goldilocks rule of
"not too hot/hard, not too cold/easy, but just right."
for some more info see
OBTW -- off topic
some economics/financial videos you may enjoy
Note the convergence of the viewpoints of the
progressives/liberals and conservatives against the
If you can find one, buy the blue Norton SG (seeded gel)wheels instead of
the normal white ALOX wheels. They cut cooler and don't require dressing
nearly as much as the white ones. They are expensive, but it in IMHO.
Which opens up an even cheaper option for the typical home/hobby
Use your belt sander to rough, and then go ahead and finish using
the green rocks [silicone carbide] that came on the grinder. To
be sure the wheel wear will be slightly greater, but for the
volume of the typical home shop this won't a consideration, and
you avoid buying a c.30$US +S/H white rock for a long time, and
use up the green rocks.
As mentioned I like the blue zirconium oxide belts for tool
roughing as these seem to cut quicker and cooler.
For anyone that is interested most mill supplies should stock but
for an example click on.
?PMPXNO=1650121&PMT4NO=36655511for info on zirconium oxide abrasives click on