Thread: The Ultimate Grinder?

Originally Posted by brendan stemp

I'm interested in why you think speed isn't and issue. My thinking is (and I speak with very little authority on this) the slower the speed the less likely I would be to burn the steel.

Brendan, your right about speed being an issue when grinding carbon steel tools. Too much heat will damage it. Not so the case with HSS.
When first I took up turning in 1982, I too was concerned about grinder damage to my HSS tools. Back then, we didn't have the internet, so I wrote a letter to Jerry Glaser (a metallurgist) asking him if heating up the edge will de-temper and do irreparable harm to the edge. I always used regular gray wheels on the grinder...didn't opt for any pink or white friable.
Jerry's reply put me at ease ~ heating up HSS to a red glow will NOT harm the edge. Cooling the edge with water WILL damage it (micro-fracturing).
Now, it's my understanding that there are new type alloys out that you do not want to heat up...I do not know what they are - someone with more knowledge than I should know which alloys they are.

Here's another source to bear this out:


From: "Ed Huntress" <[email protected]> Newsgroups: rec.crafts.metalworking Subject: Re: Flycutter from hell? Date: Thu, 17 May 2001 01:28:40 GMT >>I remember spending several hours (over the course of a few days) grinding an HSS bit downto a .064" wide 'cutoff tool' 3/8" long for a particularly nasty groove that had to be cut.<< Most people are too cautious grinding hss. You can grind it until it starts to glow red. It actually cuts pretty fast when you apply enough pressure. So does the grinding wheel. <g> Ed Huntress

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From: "Ed Huntress" <[email protected]> Newsgroups: rec.crafts.metalworking Subject: Re: Flycutter from hell? Date: Thu, 17 May 2001 15:37:47 GMT >>I have always used water (usually room temperature or so) to cool HSS when grinding tools.<< Never, ever, ever. Change your thinking on this quick. High speed steel is tough stuff, but it can't tolerate that kind of thermal shock. Neither can most other high-alloy tool steels -- and the low-alloy and straight-carbon types (O-1, W-1) can't take the heat to begin with. I use water to cool mild steel when I'm grinding it, and I'll do it on woodworking chisels and plane-iron blades, which I never let get hot enough to show color, anyway. My good ones are never allowed to get too hot to touch. At those low temperatures it's not much of a risk and water dips speed the operation a lot. But you can't grind HSS very well without getting it hot. It can take the heat, right up to a low red glow. What it can't take is thermal shock. >>I hold HSS barehanded and fairly close to the area being ground and I give it a few swishes when I start feeling some warmth.<< That's fine for grinding woodworking chisels, but it's too dainty for grinding high-speed steel. If you can handle it you aren't applying enough pressure to grind it efficiently. HSS requires some pressure, which is hell on grinding wheels but it beats taking an hour to grind a threading bit from a blank. I hold HSS bits with Vise-Grip pliers when I'm grinding them. Sometimes I clamp them in a toolholder and hang onto that. I can grind a threading bit from a 3/8" blank in about five minutes. Ed Huntress </[email protected]></g></[email protected]>

Yep, hot HSS and water don't mix, just asking for flying bits of steel whilst turning. I know ever time demos at any club, the first thing he does is throw the tins of water next to the grinder away. Second offence results in more specific aim when throwing away

Originally Posted by Ed Reiss

Jerry's reply put me at ease ~ heating up HSS to a red glow will NOT harm the edge. Cooling the edge with water WILL damage it (micro-fracturing).

That's my understanding. Couldn't say it any better, and wouldn't attempt to do so, for when it comes to woodturning steel Jerry is the man.

Adding a little colour to HSS just makes it more colourful...

If anything, I would like my grinders to run faster...

I use an 8 inch white Alox wheel on 1725 RPM grinder. I have several carbon steel tools that came with a lathe or bought in a box full of stuff at auction.

A quick one or two second swipe on the grinder will sharpen them and not harm even the thin small spindle gouge.

The thick blunt edge of a scraper will stand more time on the wheel.

Even if over heated a tool will cut for a bit, then need resharpening.