Why CBN, or other coated steel wheels are not as good as a a matrix grind wheel......

Discussion in 'Woodturning Discussion Forum' started by odie, Apr 19, 2014.

  1. robo hippy

    robo hippy

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    You can do a negative angle with the robo rest. If you push the rest past the last stop, and slip the pin through so that it rests on the frame of the rest and not through the tubes, you get about 75 to 80 degrees negative, which is in the range of scraper angles. It may be a bit less on the Oneway compatible version, but I don't have one of those set up in my shop. I will play around with it next week some time. Today, I have to get my sun flower jungle mostly planted.

    robo hippy
     
  2. Richard Findley

    Richard Findley

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    I've been reading this with interest. I've been tempted with a CBN for a while now but not sure I can justify the expense.

    The grinder I use is an 8" slow runner which is fitted with its original 120g white wheel. This is now about 5 years old and has only lost about an inch of diameter. The whole set up cost me about £135 which is about 230 dollars. A new CBN wheel (just checked the D-Way site as it seems most popular) would be 185 dollars plus shipping to the UK. A new White would cost me about £40 (70 dollars)

    Everyone I have spoken to raves about CBN, apart from one friend of mine who thinks that, although it gives a really nice edge, it doesn't seem to last long. He is the only one, but I trust his judgement as a professional turner with a scientific background.

    I know of one pro that says his CBN is beginning to show signs of wear after a couple of years of use.

    Just can't decide. Will be in Phoenix so look forward to joining discussions on the topic. Might also like to see that Robo rest too if you're in a booth RH!

    Cheers

    Richard
     
  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I just checked the OptiGrind web site in the UK and you might possibly get a better price than ordering from D-Way over here. A nice feature of their CBN wheels is abrasive on the side.

    Here is what they had to say about diamond abrasive wheels:
    Diamond is chemically pure carbon. When it is used as a grinding grit it works extremely well with tungsten carbide or glass. With steel, this is a different matter: At comparatively low temperatures the diamond (carbon) forms carbides with some of the ingredients you have in every steel, nickel, chromium. That means the diamond is gone, your diamond grinding wheel is destroyed.
     
  4. robo hippy

    robo hippy

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    Richard,
    I do have a booth there, and will be right next to Doug Thompson. Now isn't that a dangerous set up!!!!

    robo hippy
     
  5. Sergio Villa

    Sergio Villa

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    I do not dispute your quotes of course, but Eli Avisera as you mentioned honed his skews. Honing primarily is done to remove the burr and secondarily to remove other imperfections left by the wheel and thus polish the edge. If you look at a skew just sharpened with a CBN wheel you can notice an heavy burr that can be felt also with a finger. It may vary with the speed of the grinder etc but the burr is there and visible. That burr interferes with the edge and dulls it while using the tool and then is removed by the turning wood but at this point the edge is no longer perfect. It still cuts but is not perfect. In spindle turning, with a perfect edge the skew can easily leave a surface that does not need sanding. The burr interferes with this.

    The edge left by the CBN wheel is identical to the one left by a similar grit composite wheel. The difference is in the less heat produced and faster grinding.
     
  6. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Not in my limited experience using a 180 grit D-Way CBN wheel. In fact I would say that the edge quality was almost as good as one from the Tormek. There was no discernible burr. Do you have the skew lying flat on a tool rest so that there is no bevel pressure against the wheel or are you using something like the Wolverine to sharpen a skew. There will be a big difference because the greater grinding pressure from using a Wolverine jig would definitely result in a burr. I would still hone the edge after sharpening on a CBN wheel, just as I would hone the edge after using the Tormek wheel.
     
  7. Sergio Villa

    Sergio Villa

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    Bill, I (try to) sharpen the skew like Eli Avisera does it: I use the platform to rest my hand an go down and up with the tool making the edges round and not concave. No pressure at all, just the weight of the tool. The CBN wheels leaves a burr in any tool in fact scrapers are often ground on CBN wheels, see Robo.

    Any rotating grinding wheel that touches a metal surface leaves on it a burr, irrespective of the direction of rotation. The burr is not an accumulation of metal particles but is due to the pressure of the rotating wheel touching the metal,heat and pressure greatly influence this process but the formation of a burr is inevitable.

    Industry spends enormous amount of money in removing burrs from machining activity. You know this.

    The edge is related to the grit. The Tormek wheel set on a fine grit is equivalent approximately to a 1000 grit stone, it is lubricated and cooled with water and run at 90 rpm and in spite of this it leaves inevitably a burr. In fact, the burr left by the Tormek on a scraper leaves on the wood a much finer surface than the burr left by the CBN wheel.
     
  8. robo hippy

    robo hippy

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    Well, I can raise a burr with any wheel I have ever used, including a 320 grit CBN matrix type wheel, 180 and 80 grit CBN electroplated wheel, and a Tormek both with the coarse wheel and the 'graded' wheel where you could supposedly load it so it was a finer grit. How much of a burr you get depended on the coarseness of the wheel, and how hard you pushed into the wheel. The coarser the wheel and the more sharpening pressure you use, the bigger the burr is. With a very light touch, you might get 'no discernible burr' which to means there is one, but it is pretty tiny. I think the only way to get rid of any burr is to hone it off, or break it off as you turn if you have a fine wire burr. I do know one turner locally who is self taught and is a master spindle turner. She uses a 6 inch, 60 grit grey wheel and doesn't hone. Go figure..... I have been told by a number of people that it is impossible to burnish a burr on high speed steel with a hand burnisher. Well, I can do it, and not because I am using brute strength.

    I did try an upside down grind on my scrapers for some turning this afternoon. General impression is that it is not any sharper for a shear cut, and for sure dulls/bends over/breaks off way faster than the right side up burr. I was able to get my rest to about 75 degrees, or 115 degrees depending on how you look at it.

    robo hippy
     
  9. Jeff Deutschle

    Jeff Deutschle

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    When there is debate about tool sharpening at our club, the dry-wheel, non-jig crowd are usually silenced with statements like "I'd rather be turning than sharpening." or "A jig gives you the same geometry every time." The reason I tend to be silenced by these statements is the falseness and stubbornness of the arguments hides the ignorance behind them. There is a saying "Respect fools to avoid noise." I can keep my tools sharp with a quick honing and never leave the lathe. When I do regrind, I don't have to mess with a jig. When using a jig, the geometry does change depending on how long the tool is kept at a given part of the sharpening swing.

    What I think is really going on is people look to gadgets to solve their problems. It seems a quick and easy thing to get x-brand grinder with y-brand wheels and z-brand jig and you too will be "turning like a pro!" After all, how can you expect to turn like Mr. McGillicuty (or whoever) unless you have their "signature" grind and t-shirt. (The wood can tell the difference and won't behave, you know. ;) )

    The thing is, for the vast majority of us this is a hobby not a profession. Time should be spent on really learning what you are doing. I'd rather turn one bowl a week and learn for myself how different grind angles affect the cut than knock out half a dozen and not learn a thing. (But then I am more of a spindle turner, that actually likes to use a skew, and the AAW, this forum, and our local club is really about bowls, bowls, bowls. sigh...)

    Consider this. The act of presenting a tool to a spinning piece of wood is very similar to presenting a tool to a spinning abrasive wheel. If you can do the one, you should be able to do the other. If you can only do the one, you may be able to learn something by doing the other.

    Anyhoo, this is just the perspective of a dedicated hobbyist :)
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Sergio, you are correct that there is always a burr -- even with the Tormek. I try to remove it as much as possible on a skew by flipping the tool from one side to the other and making a feather light pass across the stone just to eliminate the burr as much as possible after the tool has been sharpened.Most of the time I can't see the burr except for maybe a glint in direct sunlight. A quick honing on the leather wheel gets rid of that last remnant of a burr.

    About the edge smoothness being related to the grit -- yes, but that is only part of the story -- the difference between applying heavy or light tool pressure is more noticeable than just changing grits. You mentioned that you use an 80 grit CBN wheel so it would not be surprising that the edge is the same as with a matrix wheel. Generally, the 80 grit CBN wheel is for rough shaping and the 180 grit CBN wheel is used for sharpening. Even at 180 grit it removes steel at a surprisingly fast rate compared to other types of abrasives. I think that if you try a 180 grit wheel, the difference in edge smoothness would be quite noticeable.

    With the Tormek, given that it runs cool, any discernible burr isn't going to be very useful. The way that I create a burr is first hone off any remnants of a wire edge and then use cabinet scraper burnishing tool to raise a burr. I prefer this type of burr over the type left by a grinder because it is more aggressive and much longer lasting. I create the burr by first pulling the burnisher across the top surface and then across the bevel surface. It takes some practice. If too much pressure is applied it will cause the burr to roll back too far. If the pressure is too light, the burr might not develop. Use only one drag of the tool or else it will cold work the steel (cause it to be brittle). If you haven't tried this before, I think that it would be worth giving it a shot. Who knows, you might even like it. :)

    BTW, those folks who say that you can't use a burnisher to raise a burr might be doing it wrong. It actually takes surprisingly light pressure from the burnishing tool to do it right.
     
    Last edited: Apr 21, 2014
  11. robo hippy

    robo hippy

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    One interesting thing about the CBN wheels, the 80 grit CBN wheel leaves a much more polished surface than an 80 grit standard wheel. If you use the matrix type with about 3/16 inch of abrasive mix bonded to an aluminum hub (similar to the Woodcraft diamond wheel, not sure if they carry it any more or not), the surface is even more polished. I don't know why this happens. I do go back and forth between sharpening tools on my 80 and 180 grit wheels. I can't really say I notice much of a difference in the performance cutting edges. Minimal at most. This brings us back around to the Mahoney 'I like the more serrated edge because it cuts better'.

    There are a lot of myths about the free hand platform sharpening. One is that it wastes more steel, or that you grind off more when compared to jig sharpening. This is just not true. Some of the free hand sharpeners do use a very coarse grinding wheel. This could be part of that. A lot of us tend to way oversharpen, which means instead of one pass to sharpen, we make several. This does waste steel.

    Another is the changing geometry/facets/inconsistency of free hand sharpening. My gouge noses never seem to be perfectly centered. The wings never seem to match perfectly. There are tiny facets in the bevel. I had the exact same problems when I used jigs. Point to make here is that the tools do still cut, and cut well. Next time to the wheel, I correct a little, and turn some more.

    Finally the part about it is too difficult for a beginner to learn. Well, the exact same set of skills you use to turn, are used to free hand sharpen. Anchor the tool on the tool rest, rub the bevel and cut. You roll and sweep your tool just like you do when cutting wood.

    robo hippy
     
  12. Sergio Villa

    Sergio Villa

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    I have an 80 grit CBN wheel exactly for the reason you mention: shaping the edge. With two exceptions, scrapers and skew. The reason is that with a diamond hone I usually get a satisfactory edge on the skew, and I rarely use the scrapers for finishing cuts. When I need that special edge I use the Tormek.

    PS: another big advantage of shaping with an eight inch wheel and sharpening with a ten inch wheel (Tormek) is that in this way one gets a beautiful and tiny secondary bevel to ride the gouge.
    Unfortunately this is not happening on my Tormek because its wheel is approaching the seven inch mark.
     
  13. hockenbery

    hockenbery AAW Advisor Staff Member

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    The big issue is that it takes a long time to learn to sharpen without jigs.
    An expert at sharpening probably makes a better edge with less grinding than a novice with a jig.

    I use an Ellsworth jig for my bowl gouges, it is the only tool I sharpen with a jig.
    Spindle gouges just the wheel and the top of my thigh for support.
    Scrapers, skews, parting tool a platform
    Hollowing tools the platform to rest my hand on
    Michelson grind the platform to rest my hand on.

    Sharpening with a jig is not fool proof. The tool's edge still has to be moved over the wheel.
    However sharpening with a jig can be taught and learned in a few minutes and produce consistent results.

    I used to sharpen my bowl gouges with just the platform and got good results but I lacked the consistency to keep the grind in the original profile and on occasion I would take off too much in a spot. This required several minutes to reshape the gouge to the target profile. The jig made every sharpening the correct profile and saved the corrective grinding that I would have to do every so often. The corrective grinding is what removes more steel than the jig.

    Jigs are really fast to use. But it is a choice.

    Al
     
  14. DOCworks

    DOCworks

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    Odie, I think that your statement is correct, but I don't think you believe it unless others outcome is done your way. Otherwise you wouldn't have gone on about the easy wood tools. They can start with 40 grit (I'm kidding guys) and work to the same finish as anyone else, although there will be a lot more dust. I don't care for the easy wood tools (except for certain situations) and use "traditional" tools from Doug T. I have and use Norton 3x, SG and 4 CBN wheels for D-Way. I have balanced and used the white wheels, gray wheels and the Nortons AND I have a tormeck (a very expensive dust collector). I believe if you had put "in my opinion" in your title it would have been a better statement rather than giving the accretion that you have compared fully the wheels in question. I have. I love the Norton 3X's best bang for the buck. The SG's put a beautiful edge on a tool, but are more expensive AND the big issue I have with them is this if they are out of balance you can't fix them. They have a 5/8" hole so all you can do is get the wobble out, but even if you get the wheel perfectly round it will still have vibration. The 3X has a 1" hole and you can work with that. You will say well you should have sent it back....thanks, I didn't think of that. The CBLs are expensive, but I don't have to balance them, they don't have wobble, I don't have to surface them AND I don't have matrix dust in my shop or lungs. This is a big issue with me since my diving accident in '86', blew out my left lung, I had to even quit smoking.

    While I like and respect your opinion; on this I think you are wrong.

    I do think you are spot on about sharpening! This is a skill that we don't not give enough attention, respect or education too. While I think your process is wonderful for you, I don't want to spend as much time with a hone. So I start with 180 grit sandpaper instead of 220.

    One more point I would like to make is this, I am very picky about my tools and how they are sharpened and as more and more turners are getting the CBN wheels I feel less of a need to take my grinder with me. We have a group that meets every Wednesday night out at Danny H's house and since the purchase of the CBN all I have to take is my "special" Don Geiger arm and varigrind and my tools are sharpened just like at home. Same with our clubs grinder. Now I'm not suggesting everyone one needs to buy one, I'm not, but I am pointing out a often overlooked benefit.

    CBN wheels while not perfect...there is someone out there selling a version for around $125 which is very close to your SG wheel...you can have mine after you pry my gun out of the other hand. ;-)
     
    Last edited: Apr 21, 2014
  15. odie

    odie

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    Howdy Doc.......

    Well, yes......I absolutely do believe what I said. I base my opinions on what my results are, and I am not unaware of other opinions. Is there anything that rivals the importance of results? I feel there isn't, but no matter.....I'm willing to concede that my opinions, aren't accepted universally in the woodturning community. Clarification: When I mention results, what I speak of is results on the finished turning......not results in the grinding process.

    Another person said something that I wholeheartedly agree with.......the grinding is only a method of removing metal. Many turners take their tools directly to the work from the grinder, but if an edge that cuts as cleanly as possible is the objective, grinding is only a step in the overall process.

    I'm using a SG 80gt wheel, and it grinds cleanly and quickly with a minimum of heat......but the edge I require is not the result of what I get with the SG. For me, I hone on both sides, so the initial grinding is secondary. This same thing would apply, if I had a CBN.

    One point that is particularly valid.....in my belief......is the CBN, or diamond, will wear, and a matrix wheel will cut as well when it's worn down, as when it was new.......I think that is an important thought, but maybe not so much for someone who doesn't turn frequently.......When the latter is the case, then the CBN might last a lifetime.

    ooc
     
    Last edited: Apr 22, 2014
  16. Mark Mandell

    Mark Mandell

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    There appears to be something of a misconception operating here which is that CBN wheels are for "grinding" a tool's profile, they aren't. They are for "sharpening" an edge. Just because they are mounted on a grinder does not change their nature.

    This is more than a semantic distinction. In the broadest sense, anything that uses abrasive to remove metal is grinding, whether with a 40 grit wheel or a 4000 grit waterstone honing slip. For a turner, any rotating abrasive wheel in under 100 grit works well for shaping the cutting profile of a tool. Some professional turners I've met prefer a fresh 80-grit edge and opine that the edge produced cuts wood fibers well enough to start sanding with 220 papers; others prefer to hone to a polished edge as do wood carvers. CBN wheels in the higher grits will serve to bridge the divide between the two "schools" when working with the harder alloy steels as a light touch, a kiss if you will, on a 180 CBN will freshen the tool's edge, removing very little metal, taking 15 seconds to do. A quick swipe on the inside flute with a fine abrasive like a carver's slip will remove any wire edge and provide a micro back bevel for the freshly sharpened edge.

    The point here is time away from the lathe. People who turn for a living know that spending 5 minutes first grinding and then honing a tool's cutting edge is a waste of 4 minutes. It may be philosophically satisfying to know your tool has been "ground" like a surgeon's scalpel, but once you start sanding the wood surface with anything less than 2000 grit paper, the distinction is lost.

    CBN wheels, when properly used for sharpening high alloy steels, will "wear in" but should never wear out. They are not, however, used to replace a good quality matrix wheel for shaping a tool's profile. Both wheels have a place in a woodturner's shop provided they are used for their strengths.

    BTW: Diamond wheels should not be used on tooling other than carbide cutters. Just as a CBN wheel will be ruined by contamination if used on anything less that M2 HSS, even V15 and 2060 alloys will smear on a diamond wheel rendering it worthless for sharpening carbide.
     
    Last edited: Apr 22, 2014
  17. Sergio Villa

    Sergio Villa

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    ...a waste of four minutes....man, what a life!

    How many people here (or there) turn "for a living"? I bet very few. The majority turn for pleaure, fan, relaxation, express their desire to make beautiful and/or utility objects and eventually make some mony perhaps to cover the expenses. Satisfaction of a well don object is what count for many, I believe.

    PS: even the few that "turn for a living" in reality make or hope to make their money teaching, selling tools often reinventing the same thing many times, trying to sell DVD, and other gadgets to the majority of people who turns for pleasure.
     
  18. Mark Mandell

    Mark Mandell

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    please
    Sergio, by all means, if you wish to spend your time in the shop honing and polishing your tools, please feel free to do so. Likewise, if you believe that putting a gleaming razor-sharp edge on your gouge will make you a better turner or improve the "final result";) of what you do on the lathe, go for it,Dude, and may the Force be with you!!! :D
     
  19. robo hippy

    robo hippy

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    "One point that is particularly valid.....in my belief......is the CBN, or diamond, will wear, and a matrix wheel will cut as well when it's worn down, as when it was new.......I think that is an important thought, but maybe not so much for someone who doesn't turn frequently.......When the latter is the case, then the CBN might last a lifetime."

    Odie, I think this is a misconception. My 80 grit CBN wheel does not cut as fast as it did when brand new. They do break in a lot over the first month or 4 depending on how much you use them. Since then, it's cutting ability has not diminished at all, and it still will cut faster than a standard 80 grit wheel. The 180 grit wheel cuts much faster than a 120 grit standard wheel when new, and still cuts faster now that it is broken in. They soften up to a point, and then stop. The boron abrasives will take far more abuse than any other wheel. This is why you never have to dress these wheels. I am thinking that it will be a long race to see who dies first, me or my CBN wheels. You will be surprised if you take one for a spin.

    robo hippy
     
  20. Bart Leetch

    Bart Leetch

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    "I didn't expect I wouldn't see any disagreement. I don't own any Easywood tools either, so does this mean I can't have a valid opinion about them, either? Saying you disagree is one thing, but let's introduce a little more conceptual thinking to the mix, ok?"

    Ok some conceptual thinking.
    Said in a gentle quiet voice.

    So you have a bad heart I think we can take care of that by replacing it with this mechanical heart.

    What kind of testing have you done & is there anything that compares to it in actual use Hands on if you please & if so how does it compare?

    We don't have anything to compare it to we just believe it works.

    What experience & success rate have you had with this mechanical heart doctor?

    Well we've never actually used one before but we're pretty sure it will save your life.

    What is you own experience in the field of heart surgery & mechanical heart replacement Doctor?

    Oh I don't have any experience in heart surgery & mechanical heart replacement I'm a plumber.

    But I did read about this heart on the internet & that's why I believe it will work.
     
    Last edited: Apr 22, 2014

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