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  1. #1
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    Default The geometry of sharpening

    I have made a jig based on several examples to be found on the internet with the intention of getting a fingernail grind on my spindle gouges and an Elsworth grind on my bowl gouges.

    I am trying to figure out the geometry to get the required grind using my belt sander.

    I thought I had it licked, but not so.

    I can get a really good edge BUT the geometry is all wrong and I am a bit puzzled as to what is happening and why.

    Is there anyone who can help me out with this?? Pretty Please???

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  3. #2
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    Default

    What an interesting puzzle!
    "Fingernail grind." Is this a semicircle or one end of an ellipse? Seems to me that the axis of rotation in sharpening must go through the center of the geometric shape. No? Thus the butt end of the handle could ride in a semicircular or elliptical track/groove.

    Unless the edge was really beaten to Hello, I'd be tempted to do the first iteration, freehand, on a stationary oil stone. Repeated applications of black felt marker to see where the metal is coming off. Even 600 grit W&D paper might offer some clues.

  4. #3
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    Thumbs up

    'Tis indeed interesting RV.

    I think the shape is actually more parabolic, but no matter, it's the getting of the shape that is important.

    My freehand ability is almost non existent so your suggestion just won't work for my good self.

    I should explain a little more as I have had time to ruminate, cogitate and procrastinate even further.

    Part of the problem, I have concluded, comes from two factors:

    * Nearly all sharpening systems are designed for WHEELS.

    * My thinking is clouded by this and a certain amount of age related slowdown.

    I was, incorrectly, trying to apply the geometry of the jigs for a wheel to a flat belt. Doesn't work.

    After more doodling and Googling I have come to think that a bar mounting system, like that of the Tormek,
    will provide the solution. I have begun to see the belt as a flat wheel!

    All wheel jigs, apart from the Tormek, have a pivot point mounted well away from the wheel and, to some extent, rely on the steady hand of the operator for absolutely perfect good results.

    The Tormek jig cannot be rotated from side to side in an arc and therefore an exact grind can be achieved.

    Over the next few days I will put the new found thought processes to the test.

    Wish me well!!

  5. #4
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    Default

    The singular key to freehand sharpening is to hold your forearms firmly against your sides.
    The sharpening is done by swaying your body. With your arms locked, =you can't sweep up the edge. Any edge shaping is done in the stroke with a twisting manipulation of the tool shank with your fingers. You go with a pull stroke and STOP. Lift.
    Go back to the beginning of the stone, rotate, down and another pull stroke. It must be quite a rectangular motion to be consistent.

    This works well (for me) with the conventional western carving gouges. For all of my Pacific Northwest crooked knives, the process is reversed = the knife is stationary and the abrasive surface moves. Booger to learn but one is simply the opposite of the other.

    I used to tune up a dozen Sorby for a guy with a lathe. He sold all and a stack of wood and came out $250 ahead on the deal. I hope that the new owner is clueless about sharpening.

  6. #5
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    Default

    This explains the Ellsworth grind.
    http://eddiecastelin.com/yahoo_site_...p.54183427.pdf

    Hope it helps.

    Steve.

  7. #6
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    Thumbs up

    Thanks Stuffy, I am a great admirer of the Capt'n.

    He is a no nonsense sort of bloke with a sense of humour and an eye for the simplification of things.

    I have watched many of his videos and I actually emailed him regarding my problem. Just awaiting a reply.

  8. #7
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    Default More research

    Been doing some more research and having a good look at what I am trying to set up.

    I already have a Heligrind jig and it struck me that the Tormek bowl gouge jig is just a slightly different version of that same jig!!

    This being the case I should be able to mount a distance adjustable bar on the belt sander so that it runs across the face of the belt. I should the be able to mount the Heligrind on that and use it in the same manner as it is meant to be used on a wheel.

    I see that it will work in the same manner as the Tormek jig on the round wheel. I won't get a concave grind and that might just be advantageous.

    I've also given some thought to why I have so much trouble on the wheel and I think it is to do with the stones.

    I have a Blue Norton wheel that was designed for the Heligrind but I always get into trouble with it for any other use than rough grinding. I find the coarseness of this stone to be very off putting.The other wheel is grey and of little use for anything I do.

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