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Thread: Follow up on CBN wheels for flat woodworkers

  1. #1
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    Follow up on CBN wheels for flat woodworkers

    A short while ago I posted a warning about purchasing the radiused CBN wheels for grinding flat blades (bench planes and bench chisels) as I had been experiencing difficulties obtaining a straight grind. I posted this as I felt a responsibility having written such glowing praise about the CBN wheels I built into a grinding centre.

    It is relevant to note that the CBN wheel have been around a long time (several years at least) and have a superb reputation among turners. They were, however, little know among flat woodworkers .... mainly because they offer the capability of grinding the steels that are more commonly used by turners than flat woodworkers (such as HSS). In other words, they were designed with turners in mind.

    The performance of the 180 grit wheel I purchased from D-Way absolutely blew me away, and I wanted to share this with all that they could also work on flat blades.

    There are different shape CBN wheels available. I purchased ones with a radius as I was impressed with their potential for lathe chisels, which I also use. There are also available straight wheels (similar to standard grinder wheels). In retrospect, that is what I should have bought instead.

    There is nothing wrong with the radiused wheels for grinding lathe chisels. They are perfect for that purpose. However, they are not designed for flat grinding of plane blades, where the wheel area is narrower than the plane blade. A straight wheel would be better suited for this purpose.

    I am still 100% behind the CBN wheel. They have that much potential in my opinion. So much so, I am am replacing the radius wheels with straight wheels.

    The service and backup I have had from Dave at D-Way has been superb. Not only has he answered my emails, but we discussed the nature of the set up I have by telephone.

    Regards from Perth

    Derek

  2. #2
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    Derek I very much appreciate this.
    It is still not clear - is the slight concave center is purposeful for rounded turning tools, a different manufacture tolerance between the wheel shapes, simply a by product of the rounded corners... ?

  3. #3
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    Hi Matthew

    Some have reported a slight concave, like mine, and others have not found this. I don't know what to conclude. I have had a report from the factory to say that the section between the radii is ground flat. The radii are ground after the faces are ground flat, and it could be that on some wheels this pushes the steel up a little - I am hypothesising here. Please do not take this as fact. The point is, however, that the radiused wheels are fine for turners and that the straight wheels are probably better suited to flat woodworkers. I trust this assumption enough to get two replacement wheels, both straight.

    Regards from Perth

    Derek

  4. #4
    Thanks for the update Derek. This puts me off the fence again. i would really like a radiused edge for things like moulding plane irons and stuff like that.

  5. #5
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    Quote Originally Posted by Derek Cohen View Post
    Hi Matthew

    Some have reported a slight concave, like mine, and others have not found this. I don't know what to conclude. I have had a report from the factory to say that the section between the radii is ground flat. The radii are ground after the faces are ground flat, and it could be that on some wheels this pushes the steel up a little - I am hypothesising here. Please do not take this as fact. The point is, however, that the radiused wheels are fine for turners and that the straight wheels are probably better suited to flat woodworkers. I trust this assumption enough to get two replacement wheels, both straight.

    Regards from Perth

    Derek
    I also thought that the grinding of the rounded corners might be what causes the aluminium to bent slightly, as aluminium is know the twist when welded and such. I truly hope you are right with your assumption that the flat version will indeed be flat, because that is a lot of money to spend for a not perfect grinding wheel. do you know if they offer any guarantee for flatness? I would hesitate to spent over 200$ to get one over here once my white wheel is used up if they do not offer any guarantee.

  6. #6
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    I'll repeat what I said on the other thread. My 180 grit radiused edge wheel from D-way is still dead flat, where it should be, after 15 months use. If I go back over there today, I'll get a picture. Just based on the differences between Derek's and my results with the same wheel from the same place, I don't think the dishing problem is simply a result of the radiused edges.

  7. #7
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    Quote Originally Posted by Derek Cohen View Post
    There is nothing wrong with the radiused wheels for grinding lathe chisels. They are perfect for that purpose. However, they are not designed for flat grinding of plane blades, where the wheel area is narrower than the plane blade. A straight wheel would be better suited for this purpose.
    Hey Derek, Its interesting that the corner radius is creating problems for you with regard to grinding the blades. In most cases, the blade is wider than the wheel. You need to move the blade across the wheel uniformly to get a straight edge. I don't see why having a radius on the corner of the wheel would change that, in fact, I was thinking the corner radius would actually be beneficial to easing the blade across the wheel and not having the propensity to dig in on a corner. Much like the reason you might round over the corners on your plane blade, to keep the corner edges from digging in. I would be interested in more of your reasoning for advocating the straight wheel vs the radiused wheel

  8. #8
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    Hi Pat

    What needs to be recalled is that my grinding set up uses the Tormek BGM-100 tool rests. These move the blade in a line parallel with the tool rest. If the wheel has hills and valleys, and the blade runs along this, the blade will end up with an irregular edge. This does not apply if one free hands the blade, as I mentioned in my previous report. In fact, a curved wheel face is recommended by Joel Moskowitz in his FWW article, and it is what I used when freehanding on a white Norton wheel. If one uses the BGM-100, however, the wheel face needs to be flat and straight - as the Tormek wheel is required to be flat and straight when grinding a blade.

    Regards from Perth

    Derek

  9. #9
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    I have two CBN wheels a 180 from D-Way and a 220 from WoodTurners Wonders. I have not used either wheel heavily but have reground bevels on both. To date both wheels look flush across the top, using my engineers square to visually check them.

    I do find that the fine wheel tends to heat up faster. I still use it and the heat created has not caused a problem but the difference is noticeable.

    I have two tool rests: 1) the typical LV rest with the sliding blade holder 2) Stuart Batty rest from Woodworker's Emporium (the curved sided rest)
    Last edited by Mike Holbrook; 03-05-2015 at 9:39 AM.

  10. #10
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    Derek I am wondering if deflection of the Tormek tool holding bar could in some way be contributing to the issue you are finding? I used different tool rests on my CBN wheels because it seemed to me that when applying the higher pressure to grind a radius/bevel in a wide plane blade on my wide Tormek wheel I might have been deflecting my BGM-100 tool bar enough to cause an issue. I should probably mention that I have an old Tormek and the older rest jigs. I believe Derek and David did some strenuous testing soon after getting their wheels in order to determine how much heat these wheels produced in hard use, which might be the variable producing a different result in Derek's case. In my experience finer abrasives can cause more heat and I believe Derek's wheel had a finer abrasive than David's.

    Another possible issue could be the wheel not turning precisely on the arbor. I am having a hard time figuring out if my wheels are rotating properly. I believe both CBN wheel "manufacturers" I dealt with mentioned this issue and methods of preventing it. My understanding was that some of the arbors that come on grinders may not be perfect or retain burrs from manufacturing...I bought a washer set from WoodTurners Wonders (I think). The washers are suppose to help dial out wobble by rotating them in opposite directions. So far, I am having trouble figuring out how to tell when/if I am improving the wheels wobble. I am no geometry/physics whiz but I think these much wider/hollowed/heavy wheels compound any wobble/pressure/heat issues vs smaller solid "stone" wheels. Tormek uses an even wider wheel, but they rotate it at a much slower speed.

    Another thing I wonder about is the alloy used to make these wheels. I think the last wheel I bought is aluminum. I suspect "other" wheels may contain aluminum or other metals that might deflect under heat and pressure. I know the weight of these wheels can be hard on some grinders and the manufacturers apparently are experimenting with alloys, wheel sizes etc. to deal with all the weight. Until a sizable manufacturer, aka Lee Valley, decides to invest a sizable amount of time & money in research we may be feeling our way in the dark. I am also thinking about calling someone who forges woodworking tools, Barr Tools maybe, to see if they can offer any insight into heat and pressure with these types of metals. Maybe one of our posters can help?

    I am just trying not to do too much grinding too fast on my wheels until I am comfortable with weight/heat/wobble factors and how they may or may not affect: my wheels, my grinder and the tools being ground.
    Last edited by Mike Holbrook; 03-05-2015 at 12:13 PM.

  11. #11
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    Hi Mike

    The Tormek tool rest is quite substantial and very difficult to deflect. It occurred to me and I tried to make it do so. It would not. Using the tool rest on the Tormek is different to using it on the CBN wheel. On the Tormek one tends to use a great deal of downforce (I do), but the CBN wheel only requires a very light touch. So where would the defection come from?

    Keep in mind that my initial experience with the 180 grit CBN wheel was very positive, with a perfectly straight grind. So what happened? I bumped the set up and through it out. I could never get it back again. I suspect that I got lucky the first time by working on a sight angle - I was using the set up directly from the white wheels that the CBN replaced. The problems began when I tried to set it up square.

    Again, it is possible to freehand on this CBN more successfully than when using the BGM-100 tool rest.

    Regards from Perth

    Derek

  12. #12
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    I use the Veritas grinding stand, and guide most of the time, so I don't think the stand is the issue. The Veritas stand is very rigid as well. The other difference I noted is that I only use O1 tools. I wonder if the harder steel tools make a difference in wear. At this point, there is not enough evidence to say exactly what caused the problem, if it existed to start with, or if it presented after an amount of use. I'm sure I've used mine way more than any hobbyist woodworker would use one in a year, but again only with soft steel tools.

  13. #13
    Derek,

    Just wondering if this experience will affect the way you go about recommending tools and gear in the future. I imagine a fair number of people went out and bought a radiused wheel and a Tormek guide based on your (very enthusiastic) recommendation. If they now buy a flat wheel, they are in for close to 400 bucks. That's more than I would spend on grinding gear in a couple lifetimes. When this subject came up a few months ago, I got a fair amount of grief from a number of people for expressing skepticism about these wheels, but I think skepticism was warranted.

    Perhaps it would be a good idea to wait 6 months or so before issuing endorsements, to see if the items pass at least a minimal test of durability. I know I have certainly purchased tools and been very enthusiastic about them initially, only to be disappointed later.

    On the specific topic of CBN wheels, I'll paraphrase what I said in earlier threads. A traditional grey or white wheel, or Norton 3X, can be ground to any profile you want. That flexibility is very useful, and it also means you're not at the mercy of the manufacturer's standards for flat, straight, or perpendicular. The cutting surface can be renewed almost indefinitely, whereas the durability of cbn wheels still seems to be an unknown quantity. And even the relatively expensive white or 3X wheels are a quarter of the price of the cbn wheels.
    "For me, chairs and chairmaking are a means to an end. My real goal is to spend my days in a quiet, dustless shop doing hand work on an object that is beautiful, useful and fun to make." --Peter Galbert

  14. #14
    Quote Originally Posted by Kees Heiden View Post
    Thanks for the update Derek. This puts me off the fence again. i would really like a radiused edge for things like moulding plane irons and stuff like that.
    Just get a soft wheel. You can dress it to whatever radius you want.
    "For me, chairs and chairmaking are a means to an end. My real goal is to spend my days in a quiet, dustless shop doing hand work on an object that is beautiful, useful and fun to make." --Peter Galbert

  15. #15
    Yes that's what I do now with a 3X wheel. It's a messy wheel though, creating a lot of dust. I hoped the CBN wheel would be an answer to that, but I understand your concern too.

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