It seems that I am to be known for my button grafts, a feature on a violin that if done correctly is very difficult to detect. This is because, truth be told, it probably shouldn’t even be there in the first place, for it likely indicates that an error has been made.
Occasionally I get carried away while drawing the outline of the back plate and forget to pencil in the button, that little half-circle that rises from the edge of the upper bout and is designed to support the heel of the neck. If I don’t catch my mistake soon enough, I end up cutting out the back plate without adding this important shape into it.
A button graft is done when one needs to repair this mistake and hide it at the same time. Sometimes the graft is also needed when the wood is not big enough to accommodate the entire back of the instrument with the button included, and in this case the graft is a planned part of the build.
Here you can see I am working on rough-arching a back that I still haven’t noticed is missing the button. Can you spot the problem?
Once the mistake is realized, after the appropriate face-palms and so forth have been administered, the problem can be fairly easily remedied in a way that is not very visible if done well.
The first thing to do is to fetch the original piece of maple from which the back was cut (hopefully you haven’t thrown it out!). From this piece, I cut a blank that will become the button. I mill it down to about 5-6 mm thickness and 24mm wide.
One thing to keep in mind is that the button is in the center of the back plate, where often two pieces of maple are joined. The button should also have the joint seam in it, and should match the wood of the back as closely as possible. I try to cut the button blank from the exact spot of scrap where it would have been drawn had I not forgotten to do it in the first place.
Once I’ve got my button blank, it’s time to start cutting a mortise for it on the back plate of the violin. I’ve sometimes heard this repair called a “Dutchman Inlay,” although it doesn’t resemble the bow-tie shape one often associated with that particular sort of repair.
In any case, the graft is commenced by cutting two small vertical lines precisely 12mm each side of the center line, down to the line of the purfling, thus:
Next, the material between the two cuts is removed like this:
Now the plate is turned over, and I draw in the inlay mortise that I want to cut. This is cut into the part of the back where the neck block will cover, and also being on the inside of the violin, will never be seen.
I use a sharp chisel to clean out the mortise. I cut it to no particular depth; not too shallow, not too deep. Go by what you think is best.
The completed mortise should look something like this:
Here is another view of the mortise, showing its depth:
At this point, I test-fit my blank into the mortise and do any cleanup work on it. Then I draw onto the button blank a line for the tenon.
Put the blank in a vise, and use a knife and chisel to cut the tenon down to the line. It needs to be just right to fit in the mortise and have enough depth to level with the top plate once installed.
Here is the completed tenon on my button blank:
I glue the blank and clamp it tightly to the back:
When finished, all that will be visible are the two initial cuts, and if you are good enough, the joint will be so tight, even those will be hard to see. The longer joint is hidden in the purfling channel, so it is well hidden.
Here you can see that I just need to blend the button a little bit, to match the top of the plate, and it will be as if nothing happened.
This is a handy fix to have in one’s repertoire in case of accidents, or for those times when you want to use a piece of wood that that isn’t quite roomy enough to fit the button.