Dovetail re-visited

[Jim Hilburn]

There was a tread about how to dovetail a couple of months ago ,and the Dude neck holder jig was discussed ,and Jamie and Gavin showed their hi-tech jigs ,and I said it could be done without such fancy jigs ,with the newer builders in mind. I try to keep it simple ,and I just cut one ,no ,I mean I just cut a dovetail ,and took some photo's.
Here's a surrogate table on the bandsaw used to get a taper. It's something like 2 degree's ,I don't know ,I just slightly elevated the particle board and ran it through the drum sander.

[Jim Hilburn]

Here's the view from above. The d.t. is laid out using the 14th fret as a reference because it's common to both neck and body. You can cut several cuts on each side and go slightly past the centerline without cutting into the bottom of the opposite cut.

[Jim Hilburn]

If it's not obvious ,you flip the taper table for the outside cuts on each side of the d.t.
On the neck ,I leave extra wood on the bottom of the heel to make a good stable base for the cuts. The angle of the fingerboard is determined by the blank. I have 5 degrees from the fingerboard surface to the back of the dovetail.

[Jim Hilburn]

Here's another shot of this operation.

[Jim Hilburn]

Then ,finally ,you cut the side faces WITHOUT the taper jig. Next ,I'll cut the V shape and spend several hours with files and carbon paper fitting it so it is straight and pitched correctly.

[Jim Hilburn]

I should have mentioned that I changed to a 1/8" blade for the side cuts.

[P Josey]

Thanks Jim.....

It's great you guys take the time to share this info. This looks like a great system for making d.t. neck joints. Nice and simple.

[P Josey]

Jim....

Are those two c/f rods showing in your neck? If so, do you leave them flush with the top like that?

[P Josey]

I see now it is just one rod with the center line drawn on it.

[Jim Hilburn]

It's an LMI 2-way rod. you only need a 3/16" deep rout ,the exposed portion bares evenly on the bottom of the fingerboard ,and with the allen adjuster ,I can make a tiny opening on the peghead.

[crawdad]

I LIKE this system. SImple and pretty much guaranteed to give you the same angles on the slanted cuts for both the neck pocket and the dovetail on the neck. Thank you for sharing this. Its exactly what I needed to see today!

[Michael Lewis]

Jim, are you widening the top or the mortise after it is bandsawn, or are you making it as a straight dovetail joint?

[Darryl Wolfe]

Very nice demonstration Jim

[Jim Hilburn]

Michael ,the taper is very minor ,like 1 degree ,just enough to get the neck to wedge in.

[mandomaniac]

Nice lesson...pretty much how I did it. But did not follow Michael's question. I assumed 1)the angle between the 'end' of the tenon and the FB sets the neck angle. 2) the angle of the surrogate table sets the taper of the dovetail 3) the combination of this taper and the angled shape of the dovetail pattern (looking down at top of neck) is what locked the neck in (if fitted correctly!) and what constitutes a tapered dovetail. Please correct me if I am confused. Thanks!

[Jim Hilburn]

Maniac ,you've got it.
I've been working it down using carbon paper to show contact areas and it's a real challenge to determine where to remove wood to change the fit so everything lines up and fit's tight. Another hint is as you begin to drop in the neck ,and you get the carbon marks, don't just remove the black spots. you need to imagine that the part that isn't into the joint yet will also need wood removed from it in the same area where you are getting marks. If you only remove whats your seeing ,you will probably be causing the neck to tip forward ,and will get a tall bridge.

[Chris Baird]

I've found that if I make sure that the two surfaces of the dovetail closest to the tailpiece are perfectly machined before I ever start the fitting process it helps a lot. If the those two surfaces are perfect from the beggining all I have to do(in theory) is make sure they are in perfect contact as I fit the joint and the neck will be in perfect alignment. It is an easy visual way to see how the joint is going together without taking lots of awkward measurements. Of course I still check every now and then but have found that just keeping those two surfaces in perfect contact has kept everything right on. I too use a very slight compound angle but it is probably less than .5 degree and is easily enough for the final compression fit without having to take off alot of wood in the initial fitting phase. I think the top of my dovetail is only about .040" wider than the bottom.

[mandomaniac]

Chris....am I right in interpreting 'the two surfaces closest to the tailpiece' to be the end of the tenon on the neck and the 'bottom' of the mortise in the body?

[mandomaniac]

I amm surprised that you only end up with .040 difference....really is very little taper. I thought bottom of the dovetail was a hair less than .5" and the top was close to 3/4"

[Chris Baird]

I went to all the trouble of making a couple jigs to cut a true compound joint like Gibson does but found through a couple failure tests on practice joints that the compound dovetail didn't come out any stronger than the straight dovetail. The only thing I liked about the compound is that you can get it to compress for the last 1/8" or so. So I just decided on a straight dovetail setup with just a hint of a compound angle to allow for that compression fit. As far a the size of the dovetail goes I found that the neck block should have a litte more "meat" than the neck tongue should have. I started out using a larger tongue but found that the neck block always broke too easily in tests. So I reduced the tongue size until I was getting what I figured would be a 50% chance that the tongue would fail. The size of the dovetail on the stew-mac print is just a little bigger than the size I've found optimal for the woods I use.

[pathazzard]

It's an LMI 2-way rod. you only need a 3/16" deep rout ,the exposed portion bares evenly on the bottom of the fingerboard ,and with the allen adjuster ,I can make a tiny opening on the peghead.
Jim I'm thinking about trying one of the LMI 2-way rods. How do you go about damping the vibration? They suggest silicone. I guess you just shoot some on the threaded section about halfway down. Do you bed your's in a radius bottomed slot. So the threaded rod is welded to the body end and the nut puts pressure on the square stock and there's no need to do anything to keep the whole thing from torquing except for the width of the slot in the neck? You mention that you don't need a very deep opening in the peghead but from the pictures I've seen it looks like the nut would sit lower in the peghead than a conventional rod. That's not right?

[Flowerpot]

Jim, thanks for the pictures. It's much easier to comprehend that way.

One more question -- when you mark the neck for cutting the tenon, are your lines for the dovetail slightly wider than the marks used for cutting the neck block? I'm thinking about the fact that the neck dovetail sticks out of the neck block by 0.5 or 0.6 inches, and it would have to be a bit wider at the top than the neck block mortise, by about 0.090" (I calculate). Or to put it differently, the neck tenon has to be the same width as the mortise, measured not where the neck contacts the fingerboard but at a point 0.5" or so below the fingerboard. Do you take that into account up front when making your templates?

[Jim Hilburn]

I draw the same dovetail on both pieces, but cut to the outside of the lines.Since it's tapered,it should sit tall in the joint to start with. This is where you do the hand work to drop it into place and make sure it's going in straight. It's hard to tell if your pitch is right until it's nearly in all the way, but if you've planned it correctly, there shouldn,t be a problem.