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Thread: On the "effective" grit of a wheel

  1. #1

    On the "effective" grit of a wheel

    The grit survey reminded me of some things I hope to see some discussion on:

    I think an important aspect of wheel grit on power grinders is often overlooked. IME, the edge you get is as much dependent on your "touch" and the "tuning" of your grinder as the specified grit of the wheel.
    I would love to hear other opinions on this!
    Disclaimer: These are just my thoughts and probably worth every cent you are paying for them!

    If you use a light touch and have a fine-balanced smooth-running wheel, you are essentially riding the top surfaces of the grit, and an 60 grit wheel may be effectively performing like a 180 grit stone. The fast surface speed of the wheel makes it fairly easy to "ride the tops" and I can see the difference in the smoothness of the bevel depending on how much pressure I put on the wheel. I usually end any shaping/sharpening with a very light pass.
    The system needs to be tuned, because, if the wheel is out-of-round, it tends to "dig into" the tool on the high spots. Similarly, vibration of the grinder causes the abrasive to impact the tool as you attempt to hold the tool steady.

    I also wonder, but don't have much conjecture on the effects of dressing the wheel. Tormek maintains that their single stone produces an effective (IIRC) 200 or 1000 grit depending on how you dress it. Is their stone really that unique or are our dry stones (at least partially) prone to the same effect? Do I get a finer grit from my worn diamond dresser than my new one?
    Last edited by Kurt Whitley; 09-12-2008 at 07:03 PM.

  2. #2
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    Dunno

    I don't have the answer, but I sure would like to learn more about what you are saying! Sounds like important information to understand. I am not exactly sure if I get what you are describing. Could you explain differently how the wheel acts, in effect, like a higher grit stone? Thanks.

    Hutch

  3. #3
    The wheel will respond differently with the way you dress it. A star wheel will dig into the wheel and give a rough surface on the stone which in turn will be more agressive. Don't ever use one for turning.

    Diamond dressers are the way to go, the hand held is the most common and work well. I have found if the dresser is skewed just a bit and use your fingers as a guide against the tool rest they are very controlable.

    Single point diamond dressers are the best but run in the $80 range, Bill Grumbine sells these along with others. This type is guided off the tool rest with a adjustment screw, the wheels will run true and there is no reason to balance them. To use these touch the wheel with the diamond and make a past across the wheel, re-adjust and keep making more passes until the diamond touches the entire diameter of the wheel... now the wheel is running true.

    The last pass will change the way the wheel responds, a single pass is the best because it exposes fresh grit. Now a second or third pass without adjustment will knock off the sharp edges of the grit and the wheel will act like a finer grit because it's not cutting well.

    When a wheel is used for a while without dressing the grit gets clogged and doesn't cut and it looks like a finer grit wheel.

    Stayed up all night and my brain is not working but you get the idea.

  4. #4
    Thanks for sharing your experience, Doug.

    Quote Originally Posted by Matt Hutchinson View Post
    I don't have the answer, but I sure would like to learn more about what you are saying! Sounds like important information to understand. I am not exactly sure if I get what you are describing. Could you explain differently how the wheel acts, in effect, like a higher grit stone? Thanks.
    Hutch
    Hutch,
    Consider a piece of MDF and a piece of sandpaper on a sanding block. If you lightly stroke the sandpaper over the MDF and if you put your weight into it, you will get a different type of scratches in the MDF.
    The pass with weight will cause the cutting edges of the abrasive to dig deeper into the wood, while the lighter pass will be just scratching the surface.

    If you can, give it a try.
    First use your courser wheel.
    Sharpen a gouge as you normally would (being sure to use a "heavy" touch, if you don't normally).
    Now pick one side/wing of the tool and grind it as lightly as possible. If your wheel is out of round, don't let the tool go into the low areas, just let it barely touch on the crests.
    I believe you will see an obvious difference in how fine the scratch patterns are.
    Next, switch to your finer wheel and resharpen the coarse side with a heavy touch.
    I believe that the side sharpened on he coarse wheel with a light touch will be as fine or finer than the edge sharpened on the fine grit wheel with a heavy touch!
    Let me know your results!

    Kurt

  5. #5
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    This is the picture of the single point diamond dresser.

    It is a far more convenient gadget to use than the Oneway diamond dresser.
    In the Sharpening Book by Thomas Lie-Nielson, he also used this to true up the Tormek stone.

    Doug, thanks for the tip on multiple passes without advancing the adjustment.
    Gordon

  6. #6
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    Got it

    Okay, it's clear to me now. I have kinda noticed this effect during sharpening, but I thought my eyes might not be telling the truth. Good stuff!

    On the wheel dressing issue, are you sure you wouldn't still need to balance the wheel? I say this cuz my stinkin' wheel has an annoying lateral movement. Not matter what I do I can't get the 1/16th side to side motion out of it. I don't have a wheel balancing system, but I am getting more and more tempted. It's a nice $60 8" Norton wheel, yet it causes more vibration that I would have thought. I have lived with this for a couple years now, but I imagine it's not good for the grinder motor. Do you think I should balance it? Can I dress the side of the wheel to remove the lateral wobble?

    Hutch
    Last edited by Matt Hutchinson; 09-14-2008 at 02:03 PM.

  7. #7
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    Quote Originally Posted by Matt Hutchinson View Post
    ..... It's a nice $60 8" Norton wheel, yet it causes more vibration that I would have thought. I have lived with this for a couple years now, but I imagine it's not good for the grinder motor. Do you think I should balance it?
    Are the cupped washers clamping the wheel pressed steel or machined from solid ? if pressed I would suspect that they are not locating/running true on the motor shaft.

    If this is the case, obtain some replacement machined washers or fit some tapered card packing washers either side of the wheel, adjust thickness and position until wheel runs true.

    This is what I did some 3-1/2 years ago and is going strong. (Including one method of making washers)
    Chas. just a traveller on the road of time.

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  8. #8
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    My thoughts as well...

    It's a pressed steel washer. I have been thinking that this could be the issue, but I didn't realize I might be able to replace them with machined ones. I will investigate this option. Thanks!

    Hutch

  9. #9
    Matt,
    Do you want to try something, remove the wheel from your grinder and make a bushing from wood so there is a close fit on the shaft and wheel. Not a tight fit but a nice slip fit.

    I have been wanting to try this for a long time but haven't had time.

  10. #10
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    Quote Originally Posted by Doug Thompson View Post
    Matt,
    Do you want to try something, remove the wheel from your grinder and make a bushing from wood so there is a close fit on the shaft and wheel. Not a tight fit but a nice slip fit.

    I have been wanting to try this for a long time but haven't had time.
    I tried that on an out-of-balanced buffing, it works well.

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