Sharpening tool steel

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?
Dick
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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.
-- Ed Huntress
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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.
Randal
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wrote:
<snip>

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-)
-- Ed Huntress
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On Fri, 25 Jan 2008 23:18:09 -0500, "Ed Huntress"
<snip>

<snip> =========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.
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wrote:

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.
-- Ed Huntress
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On Sat, 26 Jan 2008 02:37:54 -0500, "Ed Huntress"
<snip>

<snip> =======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 http://www.mini-lathe.com/Mini_lathe/Tool_grinding/tool_grinding.htm
OBTW -- off topic some economics/financial videos you may enjoy http://media.goleft.tv/medias/thdepressgl.m4v http://media.goleft.tv/medias/ROF_ADLIB_Economy.m4v http://mp4.dw-world.de/mp4/me/2008_01_22_22_30_studigast.mp4
Note the convergence of the viewpoints of the progressives/liberals and conservatives against the reactionaries/neo-cons.
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On Sat, 26 Jan 2008 11:58:13 -0600, F. George McDuffee

I do all my roughing on a belt sander
Gunner
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On Sat, 26 Jan 2008 10:29:56 -0800, Gunner

======================Which opens up an even cheaper option for the typical home/hobby machine shop.
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. http://www.use-enco.com/CGI/INSRIT?PMAKA85-9233&PMPXNO1881&PARTPG=INLMK32 http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO50121&PMT4NO6655511 for info on zirconium oxide abrasives click on http://www.leco.cz/download/Prospekty_EN/Matalografie/Zirconium%20Oxide%20Disks%20&%20Belts%20 (203-955).pdf http://www.nortonconsumer.com/Data/Element/Node/ProductLine/product_line_edit.asp?ele_ch_id=L0000000000000002562
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On Sat, 26 Jan 2008 14:44:59 -0600, F. George McDuffee

I buy all my belts from barbkat.
Gunner
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