Author Topic: Is the Tormek system good for sharpening concave knives / scythes?  (Read 712 times)

Offline cheater

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Is the Tormek system good for sharpening concave knives / scythes?
« on: September 14, 2020, 07:53:01 am »
Hi,
I was wondering if the Tormek system was suitable for sharpening concave knives? I have a knife that is scythe-shaped. The curved blade is a 65mm long segment of a circle of radius 73mm (the angle of the arc is 50 degrees). The blade is made of CPM 3V powder steel that has been cryogenically hardened and I would like to sharpen it to a convex bevel up to a grit that is above 3000 grit (4000-6000 is fine). I am handy with tools so if this would require manufacturing my own wheels somehow and you have a suggestion, then please let me know, or alternatively if Tormek or someone else has a product that would directly suit this sort of project.

Thanks

Offline cbwx34

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #1 on: September 14, 2020, 03:51:39 pm »
Hi,
I was wondering if the Tormek system was suitable for sharpening concave knives? I have a knife that is scythe-shaped. The curved blade is a 65mm long segment of a circle of radius 73mm (the angle of the arc is 50 degrees). The blade is made of CPM 3V powder steel that has been cryogenically hardened and I would like to sharpen it to a convex bevel up to a grit that is above 3000 grit (4000-6000 is fine). I am handy with tools so if this would require manufacturing my own wheels somehow and you have a suggestion, then please let me know, or alternatively if Tormek or someone else has a product that would directly suit this sort of project.

Thanks

Knifegrinders has a video showing how to sharpen concave shaped knives...

https://www.youtube.com/watch?v=Ug_GvJco0vM

... a good place to start.  Essentially, the edge is sharpened on the edge of the wheel, that is "rounded" a bit.

But, if you want a convex bevel, unless you sharpen freehand, you won't get it on a Tormek... it does the opposite.  You could set the bevel on a Tormek, then finish it with another method to convex the edge, but there are alternatives for creating convex edges (belt sharpener for example), that may be better suited?
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Offline cheater

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #2 on: September 14, 2020, 04:29:34 pm »
Hi,
I was wondering if the Tormek system was suitable for sharpening concave knives? I have a knife that is scythe-shaped. The curved blade is a 65mm long segment of a circle of radius 73mm (the angle of the arc is 50 degrees). The blade is made of CPM 3V powder steel that has been cryogenically hardened and I would like to sharpen it to a convex bevel up to a grit that is above 3000 grit (4000-6000 is fine). I am handy with tools so if this would require manufacturing my own wheels somehow and you have a suggestion, then please let me know, or alternatively if Tormek or someone else has a product that would directly suit this sort of project.

Thanks

Knifegrinders has a video showing how to sharpen concave shaped knives...

https://www.youtube.com/watch?v=Ug_GvJco0vM

... a good place to start.  Essentially, the edge is sharpened on the edge of the wheel, that is "rounded" a bit.

But, if you want a convex bevel, unless you sharpen freehand, you won't get it on a Tormek... it does the opposite.  You could set the bevel on a Tormek, then finish it with another method to convex the edge, but there are alternatives for creating convex edges (belt sharpener for example), that may be better suited?

Thanks. Hmm, his results don't seem to be convincing, and grinding with such a thin sliver of the wheel is bound to create uneven edges. Is it possible to get rounded wheels (even aftermarket) or to reshape existing ones?

Offline cbwx34

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #3 on: September 14, 2020, 04:47:49 pm »
You can get rounded (radiused) CBN wheels from here for example...

https://woodturnerswonders.com/collections/cbn-wheels

... but I’m still hung up on the convex edge....
Knife Sharpening Angle Calculators:
Calcapp Calculator-works on any platform
or, a couple of iOS Calculators

Offline cheater

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #4 on: September 14, 2020, 04:51:25 pm »
You can get rounded (radiused) CBN wheels from here for example...

https://woodturnerswonders.com/collections/cbn-wheels

... but I’m still hung up on the convex edge....

Not too worried about a convex edge, if I hold the knife freehand instead of using a guide the edge will tend to become convex on its own. Thanks for the link - can you recommend other places that sell such wheels? I'm mostly looking for (synthetic) stone, diamond based sharpening tools aren't that great for powdered steel as I understand.

Offline cbwx34

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #5 on: September 14, 2020, 05:27:15 pm »
...
...I'm mostly looking for (synthetic) stone, diamond based sharpening tools aren't that great for powdered steel as I understand.

I don't know what you mean about this, but pretty sure that's not true.  (Plus CBN isn't diamond).

Anyway, I sent you a message.
Knife Sharpening Angle Calculators:
Calcapp Calculator-works on any platform
or, a couple of iOS Calculators

Offline cheater

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #6 on: September 14, 2020, 05:31:37 pm »
CBN isn't diamond

Oh interesting, I didn't realize that was a different material, never heard of it. I thought it was diamond. Thanks for correcting me!
« Last Edit: September 16, 2020, 04:52:46 am by cheater »

Offline Hannsi1957

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #7 on: September 22, 2020, 09:30:41 pm »
it`s very easy to grind a convex knife if u use a pin pivot and a laser
way more difficult to grind a concave wether u have rounded edges on the stone

cheers Hanns

Offline Ken S

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #8 on: September 23, 2020, 04:09:31 am »
You can easily grind radiused corners on your SG wheel with the coarse side of the stone grader.

Ken

Offline brute

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #9 on: September 25, 2020, 02:19:27 pm »
There are knives where the blade is ground convex [camping,hunting,bushcraft,] then there are knife blades that are ground with turns & curves. Are we talking about [camping ,hunting, bushcraft],or turns & curves?

Offline cheater

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Re: Is the Tormek system good for sharpening concave knives / scythes?
« Reply #10 on: September 25, 2020, 03:42:39 pm »
There are knives where the blade is ground convex [camping,hunting,bushcraft,] then there are knife blades that are ground with turns & curves. Are we talking about [camping ,hunting, bushcraft],or turns & curves?

It is scythe shaped. There's more information in the original post, and in the thread topic.