Grinding Wheel Wobble?

Discussion in 'Woodturning Discussion Forum' started by Tom Albrecht, Oct 1, 2017.

  1. Tom Albrecht

    Tom Albrecht

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    How much CBN circumferential wobble is acceptable?

    I have three high quality 8" CBN wheels mounted on two different grinders. Composite stone wheels faces can be trued up with a diamond tool or special stone. That obviously can't be done with the CBN wheels.

    This is the best way I can describe it:
    When the grinders are shut off and slowing down, if I hold a tool on a sturdy rest and just ever-so-slightly touch the tip of the tool to the spinning wheel, it sounds like ring of an old fashioned telephone bell as the steel grinding wheel body rings with each light bump of tool. It is not severe, but it is noticeable even when the machine is fully on.

    Is this common?
    Is it my grinders (Jet and Dayton)?
    Can anything be done about it?

    Thanks,
    TA
     
  2. john lucas

    john lucas

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    The best option would be to find someone with a dial caliper and check the grinder shaft and then the CBN wheels. Something is amis. Without a dial indicator the first thing I would try is loosen the nut, rotate the wheel a little and tighten and try your test again. Do this several times if it persists. Is there any wobble to the wheel. If there is wobble left and right then that would cause the outer surface to be out of true. If that is the case then the washers holding the wheel are probably the problem. New washers would be the best bet but I have shimmed mine with paper shims to get wheels to run true. I know someone sells high quality washers for grinders. Can't remember who it is. Possibly Ken Rizza from Woodnwonders or Don Gieger.
     
  3. Tom Albrecht

    Tom Albrecht

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    Thanks John, I am using the spherical washers, but those are for side-to-side wobble.
     
  4. John Torchick

    John Torchick

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    Check the hole in the wheel. I got a Rikon low speed grinder and the fine wheel was way off side-to-side. I tried several things and finally took it off the shaft. The hole was drilled at an angle! Rikon sent me a new wheel. Thanks, Rikon!!!
     
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I have experienced what you are talking about on the 10" CBN wheel on my Tormek. While the concentricity of the bore with the outer diameter is probably extremely good, there are a few things that can create an apparent eccentricity:
    • Shaft diameter. For small NEMA motors the tolerance in shaft diameter is +0, -0.0005"
    • Bore diameter tolerance. For the aluminum CBN wheel on my Tormek the hole tolerance is -0/+0.001"
    • The major contributor seems to be the nickel electroplating thickness of CBN crystals onto the wheel.
    • I doubt that your "trued" matrix wheel was truly as true :D as your aluminum or steel CBN wheel. It's just the new sound that has caught your attention.
    Initially the coating on my CBN wheel felt surprisingly coarse for a 1000 grit wheel. However it didn't take long for it to feel much smoother. Since I ran my wheel in water, I was able to collect all of the CBN crystals that sloughed off the first few times that I used it. It was really surprising to see how the water sparkled with CBN crystals floating around while all of the steel particles were caught by a rare earth magnet.

    I can still hear some of the interrupted ringing sound, but really the sound is just the difference between a metal wheel and a matrix stone wheel. I don't suppose that you are seeing enough eccentricity to make the grinder vibrate nor cause the tools to bounce while being sharpened. I think that we'll be shifting some paradigms as we get used to the differences.

    BTW, I definitely prefer running the CBN wheel in water rather than dry despite the need to dry the wheel when done and not leave it sitting in the water.
     
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  6. Emiliano Achaval

    Emiliano Achaval

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    I have a grinder as good as you can get, and industrial 8 inch Baldor. With 2 CBN wheels from DWay tools. I have a little side by side when I turn it on, once it gets going, smooth as a baby. Last week I bought a $142 Variable speed 8 inch grinder at Lowes. I put my white wheel and the blue one, so I can sharpen my hand chase threads tools, a lot are old steel... What a difference a $1000 makes!! The Delta looks like a toy compared to the Baldor, trued the wheels with the Don Geiger tool, at least they are running straight...
     
  7. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I never understood the rationale of the variable speed of that Delta grinder especially since the range is about 1800 to about 3600 RPM. Initially I was disappointed that the CBN wheel on my Tormek didn't leave a smooth bevel. It seems to be wearing in and leaving a smoother bevel so I'm hoping that with a little more wearing in it will be comparable to the standard Tormek gray stone. I have a lot of tools that can't be sharpened on the CBN wheel (hand chisels, plane irons, knives, scissors, jointer blades, and planer blades) so I bought a new standard Tormek stone as well as a Tormek silicon carbide "Blackstone". In addition to sharpening HSS, the Blackstone can also touch up tungsten carbide cutters.
     
  8. Emiliano Achaval

    Emiliano Achaval

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    The slowest speed on the Delta feels really fast... I wouldn't recommend it to a beginner... I also have lots of things to sharpen, machetes, an axe, lots of knives, the old English chasers. Mike Mahoney visited me, with his wife a few months ago. He asked why I bought the fine grit can, not even the finest, I think is about 180, he says all his are coarse... I have been using my coarse one more often...
     
  9. john lucas

    john lucas

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    I have played with course grinds, I prefer finer grits but then I turn mostly dry wood. There are a few good wet wood turners who prefer a courser grind. Maybe someday I will have time to do an experiment and see.
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Some turners prefer to brutally rip through the wood with ragged saw edged tools while others prefer to gently slice through the wood without the wood realizing that it is being cut.
     
  11. john lucas

    john lucas

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    I prefer to surprise the wood. Of course some times it surprises me with a catch and I have to discipline it but we work that out.
     
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