Follow up on CBN wheels for flat woodworkers

[ian maybury]

Hi Tom. Just in case - i'm not arguing against CBN wheels, only suggesting that they may need a bit more care in choice of bench grinder they run on for sharpening edge tools than a friable stone. Those Metabo machines look dead nice, and your experience confirms that. I thought of one, but could find one locally or in low speed format..

[Tom M King]

Yeah, I dont' think Metabo makes a slow speed one. I decided to try a regular, full speed one to see what it would do, and it works fine. You just need a good touch, or too much could be taken off so quickly by anyone who is normally heavy handed. If anyone does go this way, develop the touch with cheap chisels first.

[Chris Parks]

You don't need a dial indicator to clock the concentric run out of a wheel. Fix a piece of stiff wire to the grinding rest and use a feeler gauge to set the gap from the end of the wire to the wheel. Turn the wheel by hand and see if it runs out and measure the smallest air gap with feeler gauges.

[Derek Cohen]

Ian, your comment about the "lack od adjustability" is spot on. Friable wheels, whether they are used on the Tormek or a dry grinder, may be trued or adjusted to run parallel to the BGM-100. With the CBN wheel, one has to adjust the BGM-100 to the wheel. Because it is not friable, it must be made perfectly flat and the machine must run true. There are many ways for this system to go wrong. When it comes together it is a delight, effortless, nothing short of amazing. But getting it there is not for the faint-hearted, and for this reason I will only recommend this combination with the above cautions.

The second method of setting up a grinder for flat work is the one advocated by Joel Moskowitz, who published an article in FWW magazine several years ago. This uses a wheel with a radiuses/convex face. I think that this (single point) design wheel does reduce many of the problems above, and it is the one I would use if freehanding (it is what I used when I had a white wheel). However it cannot be used with the BGM-100, which required support across the width of the bevel face.

It seems to me that lathe chisels are far more tolerant of inaccuracies in the grinder wheel. With the exception of a skew chisel, most have rounded bevels. Most lathe chisels are used off a grinder. Heat is not a concern these days because HSS is the norm, and M4 is creeping in. Carbide is available. High grit CBN wheels are now becoming available. These produce a high enough level of polish for turners, but remain inappropriate for flat woodworkers. Further, that there is no need to grind past 180 grit smoothness for flat woodworkers since one will still need to refine the bevel with (say) waterstones. Therefore just grind to a point where you reduce the need for one stone. I was trying to explain this point to a turner on a turning forum, but he did not get it. In short, what works for one group does not necessarily work for the other.

I think that CBN wheels are amazing. But we will need to use them to their strengths, which will require a system that does not rely on friability.

Regards from Perth

Derek

[dan sherman]

Derek,

Any chance you can give us an update? How is the flat wheel doing at grinding chisel and plane blades 9 months later, are they still nice ant strait?

[ken hatch]

Ian, your comment about the "lack od adjustability" is spot on. Friable wheels, whether they are used on the Tormek or a dry grinder, may be trued or adjusted to run parallel to the BGM-100. With the CBN wheel, one has to adjust the BGM-100 to the wheel. Because it is not friable, it must be made perfectly flat and the machine must run true. There are many ways for this system to go wrong. When it comes together it is a delight, effortless, nothing short of amazing. But getting it there is not for the faint-hearted, and for this reason I will only recommend this combination with the above cautions.

The second method of setting up a grinder for flat work is the one advocated by Joel Moskowitz, who published an article in FWW magazine several years ago. This uses a wheel with a radiuses/convex face. I think that this (single point) design wheel does reduce many of the problems above, and it is the one I would use if freehanding (it is what I used when I had a white wheel). However it cannot be used with the BGM-100, which required support across the width of the bevel face.

It seems to me that lathe chisels are far more tolerant of inaccuracies in the grinder wheel. With the exception of a skew chisel, most have rounded bevels. Most lathe chisels are used off a grinder. Heat is not a concern these days because HSS is the norm, and M4 is creeping in. Carbide is available. High grit CBN wheels are now becoming available. These produce a high enough level of polish for turners, but remain inappropriate for flat woodworkers. Further, that there is no need to grind past 180 grit smoothness for flat woodworkers since one will still need to refine the bevel with (say) waterstones. Therefore just grind to a point where you reduce the need for one stone. I was trying to explain this point to a turner on a turning forum, but he did not get it. In short, what works for one group does not necessarily work for the other.

I think that CBN wheels are amazing. But we will need to use them to their strengths, which will require a system that does not rely on friability.

Regards from Perth

Derek

Derek,

Ain't that the truth.

I fiddled and fiddles to get the BGM-100 adjusted parallel on my low speed 8" grinder. It works but with the 10' Tormek CBN wheel it was off with old on with the new and go to work. Not a cheap solution but if you have a Tormek I think a good solution. I may change my mind after use but I wish I had known about the Tormek CBN wheel when I started down this road.

ken

[John K Jordan]

is the slight concave center is purposeful for rounded turning tools

I primarily sharpen lathe tools and have two CBN wheels, one with rounded corners. Both are flat otherwise. I think a wheel that wasn't flat in the middle would not be desirable for lathe tools, for example, it would make it difficult to sharpen a skew. Concavity in the center must be a goof in the productions.

JKJ

[Derek Cohen]

Derek,

Any chance you can give us an update? How is the flat wheel doing at grinding chisel and plane blades 9 months later, are they still nice ant strait?

Hi Dan

Flat. No issues as all. Highly recommended.

Regards from Perth

Derek

[dan sherman]

Hi Dan

Flat. No issues as all. Highly recommended.

Regards from Perth

Derek

Thanks for the update, I'm getting ready to pull the trigger on one for my new grinder, and it's good to hear that it's still flat.

[Don Orr]

Very interesting information-thanks for all the input. I may have to look more seriously at these wheels. I have been hesitant due to something I read in several places about softer metals loading up CBN wheels. As mostly a turner, I use a lot of HSS tools but also play with hand tools a lot. I was lead to believe CBN was originally designed for harder, tougher HSS instead of softer mild or tool steels. I do know one should never grind very soft non-ferrous metals on CBN due to loading, but is there any real concern with the tool steels commonly found in hand tool blades. It seems that you have had no issues in this regard. Can you please share any insights on this? Question is for anyone using these wheels on these steels. Thanks.

[John K Jordan]

Hi Don,

I have two CBN wheels now (one on the Tormek) and just ordered a third from Ken Rizza. I have used these wheels on both HSS and high carbon steel for turning and otherwise and have seen no loading with the standard tool steels. From what I've read elsewhere hardened steels in general should be no problem.

Reed Grey addresses this nicely:

"The advice on what you can and can not grind on CBN wheels differs a bit from manufacturer to manufacturer, but general advise is not to grind non hardened steel or other softer, non magnetic materials on them. Main reason is that they can load up and the wheel might be damaged. I have ground my bench chisels on them, and they work fine, with no loading at all. .... To me, this means, save the old grinding wheels if you want to grind away some soft steel or other things. You might get away with it a time or two, but for anything but the lightest touch ups, keep it restricted to hardened steels, not soft carbon..."
http://www.robohippy.net/featured-article/

BTW, I just noticed the other day that Ken is now carrying flat CBN hand hones in a great size: 2.75"x8". He orders these with a choice of two grits, one on either side. I ordered one yesterday with 300/600 to try it out. This might be just the thing for some of my carving tools. If it works out I might get some finer grits.
http://woodturnerswonders.com/collec...ucts/hand-hone

JKJ

[dan sherman]

I'd echo what Reed said, CBN turning inserts (for metal working) are recommended for materials over 45 HRC. High carbon steels like 1085 & 1095, are well over that in their hardened state.

[Kees Heiden]

HSS steel is not harder then good old high carbon steel. Practical values for both are in the 60 - 62 HRc range. HSS wears a lot slower because of all the alloys and it keeps its hardness at much higher working temperatures. I also don't think the common HSS steels like M2 and M4 are much tougher when toughness is defined as how well the steel survives impact damage usually tested with a kerf test.

Edit, no indeed according to Crucibel steels. M2 and M4 are less tough then A2 for example.

chooseimpacttough.gif

[Patrick Chase]

HSS steel is not harder then good old high carbon steel. Practical values for both are in the 60 - 62 HRc range. dSS wears a lot slower because of all the alloys and it keeps its hardness at much higher working temperatures.

Some of the more modern PM high speed steels can be taken to much higher hardness than that. Crucible claims Rc >70 for CPM Rex 121. The HAP-40 in my PM-HSS chisels is hardened to Rc 66 or so.

For that matter, the M4 datum in the Chapy C-Notch comparison you posted likely corresponds to a hardness of Rc 63.5.

[Kees Heiden]

I believe you immediately, but in the context of "CBN wheels are for hard and tough HSS turners chisels" I think we can easilly take the M2 or M4 example, and compare it to A2. If I am not entirely out of mind then I think O1 is even a little tougher then A2 at the same hardness.