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Thread: Put CBN Wheels on my Variable Speed Grinderr - What Speed???

  1. #1
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    Put CBN Wheels on my Variable Speed Grinderr - What Speed???

    Hey All,

    I just put a couple of CBN wheels on my Delta Variable speed 8" grinder - an 80 grit and a 180. . My grinder has a speed adjustment knob. What is the best speed to use with these wheels? Do I want slower or faster? What is the thinking with grinding on these diamond laden steel wheels?

    Thanks All - I do wish we had a sharpening board on this forum. It is such an important part of WW. I know I have seen more than one request for it. Any possibility Admins?

    Thanks again

    Joe

  2. #2
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    CBN does not have diamonds so it can be used on iron and steel with little wear and no need for flood coolant to protect the wheel.

  3. #3
    That is correct Bill, CBN are Cubic Boron Nitride not diamonds so you can’t sharpen carbide tools. I think most recommend running them on a slow speed grinder, so 1750 rpm is what I would use. Woodturnswonders.com is a good reference with lots of information, he sells them also. I think you will like them as they keep you high speed steel tools from overheating and losing their temper. I use mine dry, no water or coolant.

  4. #4
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    They cut so fast anyway, there is no reason to try to see how fast you can go. I'd start at about 1500, and see how it goes. I've been using one on a full speed grinder for probably close to five years, only because that was the first smooth one I found, at the time. I can grind something without burning a corner on it, but my helpers can't.

  5. #5
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    I have a 180 CBN on my Delta 8" VS grinder and typically use the slow speed. I mainly sharpen lathe tools and it works great. I have never had the need for the higher speed.
    Dick Mahany.

  6. #6
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    Hey Dick,

    When you say you use the "slow" speed, are you basically just leaving the speed knob down all the way? I have what I imagine is the same grinder - the Delta 8" VS one. Are you recommending I just leave the knob on the slowest or slower speeds and go from there? I appreciate the help.

    Joe

  7. #7
    Yes, dial all the way to the left. That will be about 1750 rpm. I've been running my cbns at that speed for a couple years. no issues.

  8. #8
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    Hey Prashun,

    What grit CBN wheels are you running on your grinder? I have a 180 and a 600. I find that I burn my edges almost immediately with the 600 - I have to be exceptionally careful. Its almost counter to the advertised "low heat" feature of these wheels. I am thinking I should go lower - I ordered an 80 grit wheel to add to the 180 instead of the 600. Does that fit with your experience? The 600 works and leaves a nicer finish, but the heat draw is too much. I think that denser abrasives on the 600 wheel creates a lot more friction, and hence more heat.

    Thanks so much all!

    Joe

  9. #9
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    What are you sharpening Joe? If it just chisels and plane irons, I believe most folks only use the 180. Or perhaps a 200/220 grit instead, but the 180 seems to be the one most referred to for flat work tools. They then take the 180 grit hollow grind edge straight to their stones (minus the roughest grit) to only work the very tip of the tool's edge.
    David

  10. #10
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    Hey David,

    You hit it right on the head - chisels and plane blades. I had the idea that the 600 would put a nicer finish that the 180 on my tools, but I imagine that is more for turning tools. I may be selling a new 600 grit wheel for cheap. I will put the 80 I have coming in opposite the 180 and use it strictly for the worst blades.

    Let me ask another question of you guys - when I sharpen freehand, some of the time my edges are perfect, and then other times - and this happens often enough - I have skewed the edge somehow. Some of them are really bad, which is what precipitates my grinder issues. I do not understand what is happening. I use either Trend diamond stones, or Shapton Professional stones. I have used the Veritas guide, but I would really like to get my freehand sharpening chops down better. Any suggestions on what to look for in my freehand setup?

    I am sure that is a can of worms, but maybe someone has a quick reply.

    Thanks again - very nice group of people on this board.

    Joe

  11. #11
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    Quote Originally Posted by Joe Beaulieu View Post
    Hey Dick,

    When you say you use the "slow" speed, are you basically just leaving the speed knob down all the way? I have what I imagine is the same grinder - the Delta 8" VS one. Are you recommending I just leave the knob on the slowest or slower speeds and go from there? I appreciate the help.

    Joe
    Yes Joe speed down all the way. I have found that anything between the slow and high speed settings seems to cause the grinder to surge . Perhaps the heavier mass of the CBN wheel causes it.
    Dick Mahany.

  12. #12
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    As to freehand skewing, I bet it is more so on the narrower chisels than anything else. I believe that is due to it being easier to place uneven pressure on the tip end of a narrow blade being sharpened. What I mean is, it is harder to put an even pressure across the front of a narrow blade than a wider blade and uneven pressure will wear away one side more than the other. I do it on my 1/4" (and narrower) chisels from time to time and just try to correct it when I next sharpen. Occasionally, I put the blades in a sharpening guide to straighten out the end and re establish my desired bevel angle.
    David

  13. #13
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    As someone mentioned, what you are sharpening and and the grit may make a difference. I don't often sharpen chisels and plane irons but HSS lathe tools which are not damaged by overheating. I mostly use 8" 80 and 600 grit CBN wheels and a 10" 1200 grit CBN. (Remember, the rotational speed doesn't matter, it's the surface speed in distance per time (e.g. inches/sec) that matters. I run the 80 and the 600 on 1750 "1/2 speed" grinders. I use the 80 grit for shaping and the 600 mostly for sharpening skews and scrapers. I run the 10" 1200 grit CBN wheel dry on the Tormek mostly for sharping my gouges - the Tormek runs at very slow speed. To keep the heat down for hardened carbon steel the slower the speed you can use the better.

    You can use CBN at high speed if your material can take the heat.
    You can't use diamond at high speed or the carbon in the steel messes with the carbon in the crystalline structure and degrades the diamond.

    Others have asked and I've heard pros and cons about starting a sharpening forum. I don't know if it will happen. Some people apparently have had very strong opinions about the "right" way to sharpen.

    JKJ

  14. #14
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    Quote Originally Posted by Joe Beaulieu View Post

    Any suggestions on what to look for in my freehand setup?
    I am by no means an expert (in fact at times can be downright bad at this...). But one consideration might be arm motion. If you are getting skewed edges, for me, it often means I am putting a slightly different angle or pressure on the edge when going one direction vs the other. So if you are using a back to back vs circular vs linear motion it might change all the dynamics of how your arm and fingers are holding the edge throughout the stroke.

    For example, when I try to hold for straight line/linear strokes, I think my arm rocks a little and changes the cutting angle at the tip. If I try to go side to side on the blade edge, I often get a different force during push/pull. Circular motions give a different result in one direction than if I circle in the opposite direction, so again the arm mechanics are impacting it in some way.

    So try a different direction/stroke/height/holding method.

    (again I am not an expert and learn by trial an error - I still mostly use a guide when I want to get it just right)

  15. #15
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    Quote Originally Posted by Joe Beaulieu View Post
    Hey Prashun,

    What grit CBN wheels are you running on your grinder? I have a 180 and a 600. I find that I burn my edges almost immediately with the 600 - I have to be exceptionally careful. Its almost counter to the advertised "low heat" feature of these wheels. I am thinking I should go lower - I ordered an 80 grit wheel to add to the 180 instead of the 600. Does that fit with your experience? The 600 works and leaves a nicer finish, but the heat draw is too much. I think that denser abrasives on the 600 wheel creates a lot more friction, and hence more heat.

    Thanks so much all!

    Joe
    Joe, for bench chisels and plane blades, I use 80- and 180 grit on an 8" half-speed grinder. These CBN wheels are far, far cooler grinding than a 38 grit white Norton wheel, but you still need to use common sense. Heavy pressure for too long will generate heat enough to overheat steel, such as O1 and A2.

    600 grit CBN is for turning chisels ONLY, which generally use HSS, such as M2 or M4. These are impervious to heat, and so the extra heat from grinding is a non-issue.

    My over-recommended article: http://www.inthewoodshop.com/Woodwor...ningSetUp.html

    Regards from Perth

    Derek

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