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Gouge Sharpening (Fingernail Profile)


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I have a question which might be a bit obvious to most of you, to me however not so much. I know that the optimal shape for gouges in our line of work has to have a fingernail profile. Meaning the middle of the edge protrudes more than the corners. 

My question is how do you achieve such a shape (most gouges come with a straight edge) and also how do you sharpen it. Here's the method I use to sharpen my gouges (1:00 minute in the video). I am aware of special jigs the produce this fingernail profile but they are for woodturners since it is a very extreme kind of fingernail profile.

Please if you are kind enough, do share the method that you use to sharpen your gouges, since I am convinced that the method shown in the video and the one I use are not suited for violin making gouges. Thanks a lot!


https://www.youtube.com/watch?v=m-Dy7R8xQBM

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You may find some situations where fingernail is not optimum. Roughing works better with the reverse, for instance.

I grind all of my basic shapes carefully on a hand grinder and never scrub casually to hone as the person in the video does, but carefully and the minimum necessary to bring an edge. When grinding the wheel should be square to the edge at that point which requires a fanning track for the handle, not parallel as the tool is rotated. That is, grinding scratches should be radiating, not parallel.

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6 hours ago, Michael Darnton said:

You may find some situations where fingernail is not optimum. Roughing works better with the reverse, for instance.

I grind all of my basic shapes carefully on a hand grinder and never scrub casually to hone as the person in the video does, but carefully and the minimum necessary to bring an edge. When grinding the wheel should be square to the edge at that point which requires a fanning track for the handle, not parallel as the tool is rotated. That is, grinding scratches should be radiating, not parallel.

Thank you for the reply. I am aware that not all gouges should have fingernail profile. The ones that I want to reshape into fingernail are the scroll gouges. 

However I am not sure I understand what you mean by "the wheel should be square to the edge at that point which requires a fanning track for the handle, not parallel as the tool is rotated." Partly because English is not being my native language and lack of imagination I suppose  :D

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Don't complicate things. The cutting edge of gouges should be ground flat at 90 degrees to the bevel by holding it vertically on the stone. Then sharpen the chisel as in the video until you raise a burr with the finest stone. It may look slightly curved but it will be straight. Trying to radius that edge makes it much more difficult to sharpen.

As you say the fingernail shape can be created using a grinding jig attachment which is used to grind lathe gouges, not carving chisels.

 

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14 minutes ago, Dennis J said:

Don't complicate things. The cutting edge of gouges should be ground flat at 90 degrees to the bevel by holding it vertically on the stone. Then sharpen the chisel as in the video until you raise a burr with the finest stone. It may look slightly curved but it will be straight. Trying to radius that edge makes it much more difficult to sharpen.

As you say the fingernail shape can be created using a grinding jig attachment which is used to grind lathe gouges, not carving chisels.

 

The thing is  I've used relatively straight edged gouges for the scroll. And when I cut the vertical walls of the turns, the corners tend to dig into the wood before the middle of the edge does. Leaving a rough and rugged surface when scooping the volute. A fingernail profile not as extreme as the lathe gouges but still relatively curved would help in that case. 

I don't have an example to present to you, aside from @Davide Sora's videos where most of his gouges, from what I can see at least, have a slight fingernail profile and not a straight one such as mine.

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You must use a range of gouges with the right sweep or curvature sharpened at a low angle. You also need gouges which are not too thick and clunky. If you are worried about the gouge's corners just round them over a little. Using the right gouges might be your problem, not how they are sharpened.

 

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7 hours ago, Nikos Matsablokos said:

 

However I am not sure I understand what you mean by "the wheel should be square to the edge at that point which requires a fanning track for the handle, not parallel as the tool is rotated." Partly because English is not being my native language and lack of imagination I suppose  :D

Imagine the fingernail shape as being drawn with a compass with a center point , of sorts , this you can swing the tool being ground and create a fan type pattern . 
I  like to start to start shaping the fingernail shape by knocking the corners down and not worrying about the edge at all , in fact knocking the edge back till it’s about 1/2 mm thick , this extra thickness will help prevent burning, drawing the temper of the blade , once the fingernail shape is where you want it , then using a black sharpie marker you can mark the area destined to be the edge and slowly work down the corners blending the edge as it develops. The corners will need more work as they will show more thickness .

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Yes, grinding the corners back establishes the curved edge. But keep in mind that tilting the gouge when you hold it "vertically" can reduce the corner projection and it automatically establishes the appearance of a curved edge. It just depends on what angle you look at it from. So it is not a matter of curving the edge it is a matter of what angle you grind it at on a flat stone. So don't try to curve the cutting edge just hold it vertically on the stone and tilt it so that the corners are reduced.

What you will end up with is a thin, straight edge across the width of the cutting edge. You can then hone the bevel by hand like the Seller's video until you produce a burr. It is not wise to use a dry rotary grinder overheating can happen too easily.

 

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I use something similar to the wolverine grinding jig.  Mine has a height adjustable V-arm support end and an adjustable rod length.   My  grinder has a soft "green" stone wheel and a rubber polishing wheel.  Lee Valley discontinued these rubber wheels for safety issues.  The gouge sits in the V support and the length is adjusted to the angle of the gouge.  Just rotate the gouge in the support and check the progression towards the tip with the help of a black magic marker.

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8 hours ago, Dennis J said:

You must use a range of gouges with the right sweep or curvature sharpened at a low angle. You also need gouges which are not too thick and clunky. If you are worried about the gouge's corners just round them over a little. Using the right gouges might be your problem, not how they are sharpened.

 

I am using Karlsson scroll gouges. They are considered to be some of the best for the task. And they where. However my sharpening method has made the edge profile completely straight (bevel angle is still pretty low as you suggest about 20 degrees or so) and I used to rotate the middle point of the edge around the turns to create a small cut around the perimeter of the bottom of the turns, which when I was scooping the volute would leave a very clean surface. I can't do that anymore with the flat profile. 

Apologies for my English, I hope that what I am writing makes sense.

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7 hours ago, James M. Jones said:

Imagine the fingernail shape as being drawn with a compass with a center point , of sorts , this you can swing the tool being ground and create a fan type pattern . 
I  like to start to start shaping the fingernail shape by knocking the corners down and not worrying about the edge at all , in fact knocking the edge back till it’s about 1/2 mm thick , this extra thickness will help prevent burning, drawing the temper of the blade , once the fingernail shape is where you want it , then using a black sharpie marker you can mark the area destined to be the edge and slowly work down the corners blending the edge as it develops. The corners will need more work as they will show more thickness .

I do that too, bringing the edge back a little bit making it thicker. I learned that from experience unfortunately after burning the steel on some fairly expensive chisel I own, despite owning a low speed grinder and having dipped the edge in water quite a few times. These things do burn steel very fast. Which is why I was considering buying a CBN wheel which being metal, is a great heat sink and requires minimal cooling in water, if any.

The sharpie marker is a great idea, I will definitely use that tip. Thanks a lot!

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