Setting the Neck (Creating the Neck Mortise)

A violin-style neck dovetail is all surface area. The entire surface of the neck heel that I shaped in the previous blog will be glued to the exposed surfaces of the neck mortise, which I'm just about to create. I start by cutting out the area of the top that is to be removed. By removing it first, I can keep from splitting it here during the rest of the process. First I mark it out, 7mm in from the edge, and straight across. I keep the width here a solid millimeter slimmer on either side, to give me plenty of leeway, should it become necessary. Now I score a line with my knife across the inside edge of the mortise. I repeat this until it becomes deeper, and cut all the way through the top on the outer edges.
Then I can come in with my chisel and cut away the spruce and purfling leading up to that line. I don't try to remove it all at once but instead I work in cycles, scoring the inside edge of the mortise deeper into the top, then chiseling away the wood, then repeating. Eventually, I'll have cut my way all the way down to the rib structure, exposing it and part of the block. The ribs themselves must be cut away in a very similar fashion to the top.
I come through with a fine pencil and mark my desired width at the top, then at the bottom. I draw straight lines connecting my marks, then score into the lines with my knife. I continue to score until I've gotten as deep as is comfortable into the thickness of the ribs. I still have to cut this material away, though, and I don't have the same sort of access to it that I had on the top.
So what I do is come in across the grain with my chisel, holding the chisel at an outward slant so that I create a slight bevel leading up and away from the wall created by my scored lines. Also notice that the lines I scored are once again inside of the pencil lines that mark my final desired width. Once I've removed the rib material from both sides of the dovetail by alternately scoring and chiseling, I can cut the middle away. Then I cut straight down from the inside edge of the mortise to remove the block wood. I don't want to put any angle on my cut yet because if I was to angle it too much, I'd have to sacrifice neck length in order to get the correct extension height. Once the block wood is cut away, and the sides and back of the mortise are smooth and flat (thanks again to my chisel), I can actually place the neck heel into the mortise slightly.
Now I have plenty of clearance in all directions. The neck angle is still pitched forward too much, and the neck itself is still far too high. This would be a good time to discuss exactly what I'm trying to achieve when setting the neck. The first thing I should achieve is the centerline. The concept here is that the centerline of the neck should meet with the centerline of the body and they should form one straight line through the instrument. Alternatively, the centerline of the neck should converge with the centerline of the body, precisely at the bridge location (195mm from the top edge). It is easiest to find by eye, either by holding the violin a good distance away and looking at where the neck lines up, or by centering a violin bridge in its proper position on the top, then sighting down both edges of the fingerboard to make sure I have the same amount on both sides. The problem when the centerline is off can be hard to pin down if the mortise isn't completely flat, so that's the first thing you should check. If it is, just remove more material from the side of the mortise that the fingerboard is pointing towards (and the scroll away from).
Now, I'm not ready to attempt a particular overstand just yet, but I need to measure to see exactly how close I am. Remember the overstand is the height of the bottom of the fingerboard from edge of the top. Here I am measuring it on the right. My final desired overstand is 5.5 millimeters and right now I'm at about twenty. I measure on both sides to make sure there's no twist in the neck joint. That is to say, the overstand should be the same on both the treble and bass sides of the neck. If not, I need to remove material from the sides of the mortise, more from the top of the high side and, if necessary, more from the bottom of the low side. A perfect, even joint must always be maintained between the sides of the mortise and the heel of the neck.
Going back to the neck overstand, remember that I have about fourteen and a half millimeters excess neck height to get to my final desired overstand (twenty minus five and a half). I'll need that information to determine my neck extension height, which is derived on a finished instrument by laying a straight-edge on the fingerboard and measuring up from the center of the bridge position to determine the height above the top of the extension from the neck. Thus the name. For this instrument, I'm aiming for 27.5mm. Notice I'm at about thirty-two right now. But remember that I have to lower the neck by fourteen millimeters in the process. So I add that to 27.5 and get 41.5mm. Which means my neck extension height is almost a full centimeter lower than I want it to be right now. This is a good thing. If I was too high, I'd have to adjust the mortise to pitch the neck forward, which would require shortening the final lenth of my neck, which I already established at 13cm from the edge of the top to the nut/fingerboard joint on the neck. But to pitch the neck backwards, all I have to do is remove material from the bottom of the inside of the mortise, and keep it flat at the same time.
Once the neck extension height is at its proper place, I just need to lower the neck down to my desired overstand. This I do by removing straight, even cuts from the sides of the mortise. Eventually, I'm required to plane the excess wood from the bottom of the neck heel. It's important to create a flat surface that will join perfectly with the button when I glue the neck into place. By now the neck is good and tight in the mortise whenever I check it and once I get the overstand down to six millimeters, and have a consistent 1/2 millimeter gap between the button and the bottom of the neck heel, I slather the neck heel and the mortise with glue, then clamp the neck into place, driving it down that final half millimeter with the clamp so that I'll have a nice, snug fit.
So to recap, the four main things I have to keep in mind when setting the neck are the neck centerline, twist, neck extension height, and overstand. They all have to be at my desired specs at once, but if you take them one at a time and make your cuts carefully, it's not at all as difficult as it could be.

So next time I update my blog, I'll be shaping the neck.