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. Jeff Deutschle

    Jeff Deutschle

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    Thanks, but does such a burr vanish when you start to turn? Have you noticed?
     
  2. Sergio Villa

    Sergio Villa

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    It depends from the type of burr you have which in turn depends from the speed of the grinder, the angle, the pressure the type of steel, the heat produced during grinding. Burr is a very complicated matter as you can read in any of the millions of scientific or practical articles in metallurgy.
    With this said, when you get one of those thin burrs (mainly in acute angle tools such as skews and bedans) the burr breaks off easily and quickly, in fact you can break it with your fingers. If the burr has a solid base it lasts much longer.

    In my opinion, if the burr is used as a cutting edge like in scrapers, you want a good sharp not curly burr. If you use the tool edge as the cutting edge the burr has a negative interference.

    Since many turn with the burr on, the question is: why the burrs has a little effect in turning (many people do not remove it) and why it has a negative effect on carving (every carver removes the burr from their chisels)?

    The answer rests on two points as I said previously.
    Turners finish the surface with sandpaper (all do it) whereas carvers do not do it, categorically.
    Turners use HSS or other steels more resistant to abrasion and heat while carvers use mainly high carbon steel which is a more uniform steel and reaches a sharper edge which is more heat sensitive and less abrasion resistant.
     
  3. Jeff Deutschle

    Jeff Deutschle

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    Very thoughtful answer.

    I think it is worth the time and effort to remove an unintentional burr.

    I follow your reasoning as to using sandpaper, but not the type of steel. Like if a carver did use HSS, then they would leave a burr, or a turner did use carbon steel then they would remove the burr?
     
  4. hockenbery

    hockenbery AAW Advisor Staff Member

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    Spindle turners usually hone.
    Spindles have detail that cannot withstand much sanding.

    I want to be sanding finials with 320 to start. And I try to sand only the broad spaces.

    A little more like carving.

    Al
     
  5. Sergio Villa

    Sergio Villa

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    Carvers must remove the burr because a cut is the final finish. Honing removes the burr but also the imperfections that a grinder or a coarse stone leave on the edge. Oil and a fine stone leave the best, cleanest edge. Carbon steel, in my opinion, being more uniform as a steel that HSS powder steels allows the best edge.
    The reasons why burr is not very important in turning (but the best edge is after honing!) apply also on carbon tools.

    PS: honing, in my experience, is the most difficult thing todo in sharpening. It takes close to nothing to round the edge and then is when you wish you have left the burr on!
     
  6. odie

    odie

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    Good question, and I really don't know if there is a yes/no answer to that, Jeff...... I'd say it's both, depending on the strength of the burr and what forces are being applied, type of steel, species of wood and grain orientation, the individual turners and their own sharpening techniques and applications.....etc.

    You know, I've always heard that the burr broke away, and I suppose I'm guilty of accepting it on face value. I do know that since I'm one who hones, it really doesn't make much difference if the burr (on gouges) is worn, or broken, because for me, the burr is gone either way, and prior to applying tool to wood.

    ooc
     
  7. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I think that I recall that you use the Tormek for at least some of your tools. Do you use it for scrapers? The Tormek runs without heating the steel and therefore doesn't really raise much of a burr. It's more like a wire edge and as such wouldn't last more than a fraction of a second. I generally sharpen my tools, scrapers included on the Tormek. The owners manual says that a burr is necessary for scrapers and since it can't be produced by grinding, to hone away the bit of metal on the edge and raise a burr with a burnishing tool. The manual states that it is a better burr anyway -- true or not, what else would they say? My personal experience says that it is very durable -- perhaps as durable as a bowl gouge edge if done right. The "done right" is the catch. Several years ago I was taking a class from Alan Lacer and he also say that type of burr is the strongest. He demonstrated how to do it. Of course, the most important question was, "how much pressure are you applying". He replied, "not much" along with explaining that you just have to do it to learn.

    That led me to wondering if there is a good way to tell somebody how much pressure that would get someone in the ballpark.
     
  8. robo hippy

    robo hippy

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    Well, first, with the gouge burrs, I have tried to remember to feel them after I am done using one. There is seldom any noticeable burr left after using it for a bit.

    Now, with the scraper burrs, especially on the finer grinding wheels like the 180 grit CBN wheels, even though you are going up and down the face of the bevel, with a light touch, it is almost like burnishing. Not exactly the same, but almost like that. I have honed across the bevel and raised a burr that way as well. I have no electron microscope pictures to back up my theories. The article that was done some years in the AAW magazine about burrs was BCBN (before CBN wheels).

    robo hippy
     
  9. Sergio Villa

    Sergio Villa

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    On the woodturning scrapers I use the CBN wheel except when I want a finish cut and in this case I use a 600 grit diamond stone that I pass horizontally on the bevel. I also remove the residual burr with the same diamond before raising the burr. On the McNaughton tools (I love them!) I use the coarse or fine side of a cheap double face stone (home depot!). I grind the tip of the oneway coring system on the Tormek, with excellent results, and yes, it raises a small burr that I feel with the fingers.
    I get a wire (beautiful descriptive term that I could not remember in my previous post!) burr also on the CBN wheel when I sharpen the skew, which make me think that besides the temperature the angle also have an effect on the formation of the burr. The wire burr is easily removed breaking it with up and down movements. Honing is better though!
    On the burnishing tool I believe that it is the best way to raise a burr since it does it mainly by compression which makes the burr also very compact and with a smooth edge since the burnishing tool is very smooth, essential condition for a good burr.
     
  10. Ken Rizza

    Ken Rizza

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    Run Your Grinder Backwards

    I had one of my customers who purchased some CBN wheels from me suggest turning the grinder around so that the wheels rotate upwards (like the Tormek). Never thought of doing that before but I have been doing it that way now for a couple of months and I like the results I am getting. Makes raising a burr real simple also.
     
    Last edited: Apr 25, 2014
  11. Gretch Flo

    Gretch Flo

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    Odie, Robo

    How do you each "hone"???? Gretch
     
  12. odie

    odie

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    Howdy Gretch.....

    For a long time, I used slip stones, but in the past seven or eight years, I've mostly been using the diamond coated hones. Flat surface for skews and exterior cutting edges of gouges, and cone shape for flutes of gouges. Still do use the old slip stones, but feel the better edge is created by the 600g diamond coated edge......

    ooc
     
  13. Richard Findley

    Richard Findley

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    Surprised so many people use scrapers. Not a tool I use much at all. I read an article a while back in the UK Woodturning magazine, that was as scientific as turners get, testing the finish on a piece of Walnut, at a microscopic level, after scraping with tools with burrs raised in various ways...

    It may surprise you to find out that the best finish was from a scraper with no burr, but with a polished top surface. After this, on the rare occasion that I do use a scraper, I always grind the bevel and polish the top on my oil stone.

    Thoughts...???

    Richard

    Ps, I don't hone gouges or skews. Straight from the grinder for me
     
    Last edited: Apr 26, 2014
  14. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Sorby has a hardwood scraper, but according to their instructions, it should have a micro burr.
     
  15. Sergio Villa

    Sergio Villa

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    Yes, it is called burrnishscrap
     
  16. Mark Mandell

    Mark Mandell

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    The only tool I actually hone is the skew for which I use a 6" Hard Arkansas bench stone. I do use a Hard Arkansas or waterstone slip on the inside of a gouge's flute to remove the slight wire edge (burr made by the sharpening wheel) and put a slight micro back-bevel on the top edge.
     
  17. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Initially, the Tormek leather wheel with mineral oil and polishing compound. Subsequently with a diamond slipstone that I bought from Alan Lacer.
     
  18. Jeff Deutschle

    Jeff Deutschle

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    I hone everything except scrapers, which I usually burnish, Well, I don't hone the bevel of bowl gouges when I am roughing a bowl, but do remove the burr in the flute.

    I had been using a small hard arkansas to hone the outside, and SC sandpaper for the inside, but just recently got a hard arkansas slipstone. I can quickly and easily put an edge that can shave the hairs off my arm on a skew, so I am satisfied with that. I doubt I will go for a diamond stone.

    I use a 6 inch wheel, I think that makes honing easier.
     
  19. john lucas

    john lucas

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    Richard I did a test for Betty Scarpino on scraper vs cutters. Part of the test I did was using the scraper without a burr. However I was using it as a bevel rubbing tool. It was hard to tell that it cut any cleaner when using it as a scraper with and without the burr but using it as a bevel rubbing tool it performed better. Not as clean as the gouge because my gouge is sharpened at 35 degree angle and this scraper had about a 70 degree angle.
     
  20. robo hippy

    robo hippy

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    Well, in all cuts, a shear angled cut will be cleaner than a scraping cut (cutting edge at 90 degrees to rotation of the wood). Cutting into end grain is a possible exception here, but still I have found that a shear angle still works better than a scraping cut. Negative rake scrapers seem to be an exception here but I still have found them to cut slightly cleaner at a shear angle than at a scraping angle. Both gouges and scrapers can do scraping as well as shear cuts, and they both can do bevel rubbing cuts. So, which particular tool you use is not the issue, how the tool is presented to the wood is. Bevel cuts, most of the time will leave a cleaner surface than a shear scrape, though I have found times with difficult grains, that a shear scrape will leave a slightly coarser surface, but have less tear out. Again, both scrapers and gouges can be used. It's not the tool, it is the angle.

    I was playing around with very gently sharpened gouges yesterday, and the burrs were mostly gone after turning with them for a bit. Maybe I need to try a more pressure/grinding sharpening and see how the burr holds up. I never hone gouges or scrapers.

    robo hippy
     

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