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Neck Dovetail on Slope Shouldered Instrument
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50303		 Page 1 of 1
Author:  mountain whimsy [ Wed Feb 14, 2018 11:20 am ]
Post subject:  Neck Dovetail on Slope Shouldered Instrument
Hi all. This is admittedly a baritone uke, but the concepts should be the same for a guitar. And the Uke section just does not get the attention it deserves around here! So I'm posting in the Guitar Building forum!

I finally got my dovetail jig templates set up in my neck joint jigs. I normally do bolt on, but feel I need to step up my game with dovetail joints. I did some test runs with junk wood before holding my breath and cutting into the lovely sinker Honduran and redwood on this uke. The guitars I build have a large enough flat area at the neck joint to not have to worry about the slope of the upper bout shoulders. But on this uke, the slope curves through the entire neck joint.

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The mortise went perfectly and I cut a tenon in in a dummy neck to get my head around how I would have to deal with the shoulders.
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So obviously the shoulders slope away from the narrow part of the dovetail, leaving a gap. Wood needs to be removed from the neck in order to get the neck to match the curve of the body. Chisels and flossing will get me there, but this causes the dovetail to either drop down in the mortise towards the sound hole and/or back of the instrument (a good thing as long as I plan for it). But this also makes the dovetail tenon (pin?) longer, so it must be cut back so it doesn't bottom out. Or I could get the sizes correct at the start so the neck plane matches the edge of the body, but this would result in a dovetail that needs to be shimmed.

Am I making any sense?

I've seen some fancy lever-action sanders that sand the curve into the neck, but they seem clumsy and still have the issues mentioned above.

So how do you folks handle this? I'd like to modify my guitar templates to have some more flow from the shoulders into the neck, avoiding the flat area at the joint. So this is something I'd like to get dialed in. I appreciate your input.

-Tony
Author:  Clay S. [ Wed Feb 14, 2018 11:38 am ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
What I've seen done on older instruments is undercutting of the shoulders to allow only the outside edges to make contact with the body. That will move the dovetail slightly deeper into the mortise, which may make it necessary to take some wood off the face (so it doesn't bottom out), and possibly add shims to the sides, if they become too loose (and want to slide deeper in the pocket).
Author:  Alan Carruth [ Wed Feb 14, 2018 12:54 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
I'm not sure what the problem is here. This is intrinsic to any slope shouldered instrument, and you simply have to take it into account in designing and making the joint.

On more recent designs I've been incorporating a small flat, about 3" wide, at the upper end. This allows for 'round' shoulders, but is enough to eliminate the need for under cutting the shoulders of the tenon. It's nt quite the same as a 'slope' shoulder, but does mitigate the 'chopped off' look.
Author:  mountain whimsy [ Wed Feb 14, 2018 8:34 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
Clay S. wrote:
What I've seen done on older instruments is undercutting of the shoulders to allow only the outside edges to make contact with the body. That will move the dovetail slightly deeper into the mortise, which may make it necessary to take some wood off the face (so it doesn't bottom out), and possibly add shims to the sides, if they become too loose (and want to slide deeper in the pocket).


Thanks, Clay. That's the approach I've been taking. I was hoping for some wisdom from the deep well of knowledge here. I kept moving forward with my test neck and feel confident that I'm on the right track. Started out with the neck plane a little proud, but its settled into place with a clean fit. I'll tackle the real neck next week.
Author:  mountain whimsy [ Wed Feb 14, 2018 8:39 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
Alan Carruth wrote:
I'm not sure what the problem is here. This is intrinsic to any slope shouldered instrument, and you simply have to take it into account in designing and making the joint.

On more recent designs I've been incorporating a small flat, about 3" wide, at the upper end. This allows for 'round' shoulders, but is enough to eliminate the need for under cutting the shoulders of the tenon. It's nt quite the same as a 'slope' shoulder, but does mitigate the 'chopped off' look.


Agreed, Alan. Just looking for some insight or novel approach that I could put in my bag of tricks. The shoulders on a uke don't have a lot of space for a flat. I pondered it. But my client has a very keen eye for lines. Which l appreciate. It keeps me on my game.
Author:  Casey Cochran [ Thu Feb 15, 2018 2:34 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
From where you are, I would profile the heel, getting very close to the fingerboard width and the heel triangle width. Then scribe the outline on the body and sand flat between the lines.
Author:  Haans [ Thu Feb 15, 2018 5:51 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
Casey has it about right. I would get the heel really close to final (1/16"), then scribe it to the rib on each side with pencil. Hopefully, you have enough to flatten that area dead flat and hopefully you haven't you carried the slope too far as that would will necessitate sanding through the rib too far. Do it by hand with 80 grit, then 100. If it is too much of a slope, change the mold for the next one. Just glue a little scrap on the mold and re-contour.
After that, look at the female part of the dovetail. It seems as though it could be maybe an eighth deeper in order to permit a good length of the male part. I can't tell from the photo.

Next, you should carve or chisel away the neck heel on the inside so that, finished, only the edge of the finished heel will contact the rib, as you mentioned. That will make the male part of the dovetail longer. You need to end up with a 5/8" or so male part and a 3/4" or so depth into the box This would be on a guitar.

I used to start at about 3/32" sticking up on the neck. You can hand sand with that jig block below to bring it down to flush. You will probably need to shim this one. Nothing wrong with that if you take your time and do it well. Taking a look at John Hall's vids on doing all this is important to "getting it". That V shaped block he shows is a valuable jig and worth building. You can sand the angle into the heel among other things. It does take quite a bit of time/thinking/effort to "get" doing it right. Carry on, it's worth it if you like dovetails.

While you are finishing that dovetail and the next few, think about that 1000 buck metal jig. It's absolutely worth it after setting it up accurately...
Author:  George L [ Thu Feb 15, 2018 6:57 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
Now you know why most shapes ease that curve into a flat. :-)

I agree with Haans about the depth of the mortise and John Hall's dovetail sanding block.
Author:  mountain whimsy [ Wed Feb 21, 2018 12:26 pm ]
Post subject:  Re: Neck Dovetail on Slope Shouldered Instrument
Back in the shop after a horrendous 4 day trip to Colorado. The brief Colorado part was fine. Got to see some family, and most importantly, see Bruce Cockburn play at the Boulder Theater from the front row! He had a band, so this was a treat! The drive to and from was white knuckle on snowy and icy roads. Not fun.

Casey and Hans....great input! I was able to shape the heel, as suggested, and flatten out the body in the footprint. The heel is so narrow that you can hardly notice the body flattening out to accept the heel. And the area under the fingerboard, though a wider flat spot, is hidden by the fb. So no issues there. A bit of flossing and I was in business. I had a good neck angle set when I cut the dovetail on the neck, so my fb is laying nicely on the top, with what appears to be good relief at the saddle.

Thanks for the suggestion. If I build this baritone uke again I'll likely modify the mold as suggested to flow into a flat area at the joint. I'll also shoot for a slightly deeper dovetail. I was following the Antes plans on this one which calls for the dovetail at the size that I used. It does seem a little shallow, but for a uke it should be fine.
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