Warning: Check the hardness of steel before grinding with a CBN wheel

[Joe Kaufman]

I purchased a Harbor Freight toolset several years ago, what they call their “8 Piece High Speed Steel Professional Wood Turning Set” (maroon handles). I’ve used 6 of them in one form or another regrinding on a CBN Wheel. Two set in the box unused, one a 3/8 gouge. I decided to try the bottom bowl gouge grind concept on the 3/8 gouge. It ended up that that gouge had missed the heat treating process and it was dead soft. I now have two smears of soft steel imbedded in the CBN wheel. I have been able to remove a little by picking at it with the point of a small carbide drill. Nothing else I’ve tried has much effect. It’s not that I didn’t know better than to grind soft steel, but I didn’t suspect or inspect. Anything new, check hardness with a file.

[Thom Sturgill]

I have heard that you can simply grind a tool with hard steel and it will remove the soft steel deposit. Have you tried that?

I bought a similar set when I started turning seven years ago. After grinding about 3/4" off the 3/8" spindle gouge it became unable to take an edge. Zone hardening had only hardened the very tip. I no longer recommend HF turning tools to new turners for that reason. Trying to learn to sharpen on junk is counter-productive.

[Joe Kaufman]

This happened a couple of months ago and I have since sharpened a lot of Doug Thompson's tools. The soft steel is still visible on the surface of the wheel and
I can feel a slight unevenness in the grinding in that area, not the feeling that the smear is higher that the grit.


I just checked and as you say, the HF tools are only hardened for a couple of inches at the surface at best, and the length varies from tool to tool. It would be difficult to remember to check and also to determine when it is approaching soft enough to smear. Guess I will have to give Doug some more money as the 1" skew I use is HF.

[Thom Sturgill]

You will be pleased with the improvement in cutting. My Thompson skew (sharpened ala Alan Lacer) is my7 goto skew. A round skew I made from a Thompson blank is my goto for miniatures.

[Reed Gray]

If you have a good hard scraper, like one of Doug's of Dave's, several sharpenings will take the soft stuff off. You can feel the bumps when the wheel loads up. I tried some aluminum tubing just to see what it did....

robo hippy

[Bob Bergstrom]

Possibly try flipping the wheel to the oppoisite side of the grinder to change the rotational direction. Then grind with the hardest steel tool you have. That may loosen the particles.

[Peter Blair]

Thanks for this thread Joe. I have a set and wonder if anyone can suggest a good way to test the hardness. Can I try to file them starting at the end and working toward the handle stopping when I can notch the tool with the file?

[allen thunem]

i use a rubber cleaner like what is used to clean sanding belts on a belt sander works great in cleaning up the cbn wheels

[Joe Kaufman]

Who knows what the chemical composition of the Harbor Freight "HHS" really is. Likewise the hardening procedure. I would say that it is safe to assume that it does not conform to M2 HHS specs., especially considering the price, which was about $29 for the 8 pc set 9-10 years ago. It's like the steel is fused to the plating on the surface of the wheel. Yes you can wear it down to the outer surface of the CBN Particles by aggressive grinding with hardened steel but it is still filling the voids between the CBN particles. The file test is only a surface test and not indicative of the hardness below the surface or in the center between surfaces. This is just a warning and something to consider based on my experience. IMO, it's just not worth the chance of loading up a CBN Wheel. Regular grinding wheels are fine for it.

[Jeffrey J Smith]

You might look at Dave Schweitzer's site www.d-waytools.com (http://www.d-waytools.com) - he's got information on what works for cleaning, what different metals do to the wheels, etc. Not sure where you bought your wheels, but he's a great source of information on just about anything turning related. He'd probably talk your ear off even if you bought your wheels somewhere else. A great resource and a true gentleman.

[Bob Bergstrom]

We had a club member that had about 2" of flute left on a Benjamin's Best bowl gouge. He kept asking me to sharpen it for him. I finally tried turning with it and noticed it got dulled very quickly. There was no teper left.

[Joe Kaufman]

Got it from Dave a couple of years ago. Been considering an 80 grit anyway so will talk to him.

Thanks.

[Steve Carroll]

To remove the buildup, maybe a dressing stick like these?

http://www.e-grindwheel.com/DressingStick.html

[George Troy Hurlburt]

I'm old fashion glad I don't have a CBN wheel, you are not the only who have experienced problems using them.

[Reed Gray]

The first CBN grinding wheels I had were a matrix type, in which the abrasive was mixed with some some compound, and then bonded to an aluminum hub in a layer about 3/16 inch thick. I used a very hard aluminum oxide stick to clean them. They are similar to what Woodcraft carried for a while but they were a diamond abrasive wheel. They do not work for an electroplated type wheel which is what all of the steel ones are. Taking a scraper to the wheel and sharpening it for several times will do the trick. I don't know of any other way to do it.

robo hippy

[Peter Blair]

That's really too bad George as will never experience the ease with which it make for my sharpening. Never having to worry about changing angles for whatever tool I sharpen. It is great too combined with a Robo Rest for sharpening those really small bits that I use in all my hollowing tools.

[George Troy Hurlburt]

You are right Peter. I may invest in the CBN wheels someday. But right now I have 3 grinding machines for woodturning tools with Oneway setup,Ellsworth,Jordan,Veratis,Kelton,Woodcut and others I forgot the name of. If that doesn't work I'm big trouble.

[Thom Sturgill]

You are right Peter. I may invest in the CBN wheels someday. But right now I have 3 grinding machines for woodturning tools with Oneway setup,Ellsworth,Jordan,Veratis,Kelton,Woodcut and others I forgot the name of. If that doesn't work I'm big trouble.

But the important issue, in my mind, is what kind of steel are you using? Common HSS used by turners is M2 (At least on better tools). M2 will sharpen OK on a matrix wheel but keeping it dressed properly drastically shortens the life of the wheel. M42 like Dave of D-Way Tools uses I'm not sure, but the high Vanadium steels like Doug Thompson uses creates lots of microscopic carbides that the AO wheel can not cut. It can only knock them out of the steel matrix. CBN can cut them and results in a sharper, longer lasting edge. I suspect this is true of the Cobalt in the M42 formula too and it does have more Vanadium than M2.

Cindy Drozda, who has been selling her own line of tools for years and recently switched to using blanks made by Doug for her, has a lengthy Blog post on the subject where she says she consulted some metalurgists about the issue.