This looks like a crude method, but the geometry is correct. See the curved edge?
I use a short, about 6 inch vise grip. Attach it like this (below):
The back end of the vise grip is round. This will be the pivot point, resting in the notch in the PVC toolrest.
I placed a pencil to show the imaginary line from this pivot to the middle of the curved edge. Like this (below):
:
Now place the pivot point in the notch of the PVC toolrest. Like this (below):
I use two hands of course. One holds the pivot point in the tool rest. The right hand guides the edge against the 6000x stone.
Too bad I cannot do a professional job photographing this. But it really works.
The link to my tapered violin knives is here.
Now, replace the vice grip with a simple holder. Made of bamboo. This is available at Malwart. It is used for cutting boards. I routed a 5/8 inch slot to hold the knife, which is also 5/8 inch (16 mm).
Now place the blade in the slot and attach the clips.
This design is the simplest I could come up with. When inserting the blade, adjust it so that the head of the bolt is in line with the center of the blade edge like so:
It is now ready to hone on the rotating flat disc hone.
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Now everyone should be able to sharpen violin knives on stones. I had a brainstorm which allows a very simple design. It uses neodymium (NIB) magnets. The blade just snaps in.
The magnets are 3/8 inch diameter x 1/8 inch thick.
Video is here. The jig is used with a piece of glass parallel to the stone. The screw is nylon. It will ride on either glass or some other hard smooth surface. It will not scratch the glass. The slot is routed.
This jig will allow double bevel sharpening. You just reverse the blade, left to right.
For straight edges, use finger pressure in the center of the edge. For curved edges, simply rock the blade, changing the pressure from left to right.
The most difficult part of making this jig is routing the slot. It is angled. Working out the correctly angle takes a few tries. The magnets are not expensive, although you must purchase a pack of them and pay for shipping. For fixing the magnets, use the epoxy with metal in it. It hardens quicker.