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Demystifying the Dovetail.
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=53252		 Page 1 of 1
Author:  Bruce Sexauer [ Tue May 26, 2020 8:32 pm ]
Post subject:  Demystifying the Dovetail.
I am sure this info is remedial here, but I thought I'd share anyway. I have been using this exact system for 20+ years, and variations for 15 more.

I had the camera nearby today when I cut the dovetail for the FT-000-C I am building, and I got the idea to show how easy, or not, the neck (Male) part of the dovetail is to cut. That's assuming you have serious tools and some idea how to use them.

For this method you just need a solid vice or other immobilization fixture, and at least a horse and a half router, ideally with a 1/2" collet. I'm useing 3 HP, though I haven't always. All of this work can be done with a dovetail saw and a sharp chisel, I have, and will again when the grid finally fails and western civilization collapses.

I use a different fixture for the cavity, and this system for the neck. I'll try to remember to do Part two before it's over. The two must be closely related in geometry, and cut accurately enough that minor chisel work will make them fit close to perfectly. If I made every thing the same, it should be possible to not have to hand fit, but I am the opposite, I make everything different, so I errr on the side of the dovetail not quite closing after the machining is done. If the neck stands about 1/" out of the body, everything went perfectly.

First I trim the neck blank so that the geometry is exactly what I want in skew and pitch relative to the body, this makes or breaks saddle height and whether the bridge will actually be in on the centerline of the guitar. I leave exactly 7/16" from the projected shoulder of the heel to the deepest point on the Dovetail. I make the cavity 3/32 deeper to allow for fitting and eventual possible removal.

Then I draw a center line on the end:

Image

The jig is 1/2 Finply. The 2 stews are stored where they are now between uses:

Image

The cork backed ruler is used as a guide to adjust for sweet, if neccesary.

Image

And it is set against the fingerboard surface with the hole on the centerline:

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And the 2 screws are put into the neck so the ruler can be removed:

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At 3" wide, the neck is able to support the sides of the fixture, so the router stays in control:

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Snuck in a shot of the Bridal Joint this guitar features:

Image

And the router has run all around the negative space in the fixture:

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Looks like this:

Image

A mallet and a chisel remove the support wings:

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A little closer:

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And it sits in the guitar as advertised:

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If there is interest, I may share trimming for fit in a few days.
Author:  Luthier1975 [ Tue May 26, 2020 9:53 pm ]
Post subject:  Re: Demystifying the Dovetail.
Very cool look at your process.

How do you generally approach your neck angle before the dovetail is cut?

Thanks for the post.


Sent from my iPhone using Tapatalk
Author:  jfmckenna [ Tue May 26, 2020 9:59 pm ]
Post subject:  Re: Demystifying the Dovetail.
Nice, and now the female side of the equation? Do you glue the head block in solid and rout it out of the assembled guitar body or is the head block mortise routed out and then glued on to to the top and the body assembled?
Author:  George L [ Wed May 27, 2020 9:25 am ]
Post subject:  Re: Demystifying the Dovetail.
Thanks for sharing. I, for one, would definitely like to see your entire process.

One thing: It appears that the holes left by your mounting screws are slightly off the centerline. (Which is precisely how things nearly always turn out for me!) Is that an optical illusion or a case of it being close enough that it can be addressed when finessing the fit?
Author:  G.Cummins [ Wed May 27, 2020 10:01 am ]
Post subject:  Re: Demystifying the Dovetail.
I think the trimming to fit would go down nicely.

Cheers.
Author:  Bruce Sexauer [ Wed May 27, 2020 11:17 am ]
Post subject:  Re: Demystifying the Dovetail.
I do not predrill for the screws . . . And I’m right handed. They are virtually always off center in the same way and it is easily compensated for in the “fitting”.
Author:  Clay S. [ Wed May 27, 2020 6:46 pm ]
Post subject:  Re: Demystifying the Dovetail.
As many lute makers might tell you center lines are highly over rated. bliss
Author:  James Orr [ Thu May 28, 2020 2:50 pm ]
Post subject:  Re: Demystifying the Dovetail.
Bruce, thanks for sharing this. I've been interested in trying a dovetail joint. Just to make sure I'm understanding you, your dovetail itself is 7/16" tall, and the socket is 3/32" deeper than that? Are these traditional measurements? How deep is your neckblock as a whole? I've only used a tenon up to this point, and my neckblock is 1 5/8" deep to accommodate it. Not sure if I need to adjust things for the dovetail.
Author:  meddlingfool [ Thu May 28, 2020 5:35 pm ]
Post subject:  Re: Demystifying the Dovetail.
The specific dimensions aren’t particularly important. What is important is that the gap should be accessible beneath the first fret after the body join so the steam needle can get in there to undo the joint when it comes to neck reset time.
Author:  Bruce Sexauer [ Thu May 28, 2020 7:42 pm ]
Post subject:  Re: Demystifying the Dovetail.
As i happens, my neck block is usually 2 3/4 x 1 1/2. The dimensions of the Dovetail are constrained by function, but within those parameters, there are many possibilities. My dovetail dimensions are what I though would be ideal, and are only conceptually rooted in tradition.

I did take some pictures of the fitting process, but realized that they barely assist in communicating what has to happen. I will include them anyway.

As mentioned before, the goal is to have the cheeks of the heel flat against the guitar sides at the same time as the fingerboard aims exactly to the center of the top AND the pitch of the neck is such that the saddle height of the top is in the ballpark. This needs to happen at the same time as the dovetail male and female also fit perfectly. It sounds unlikely to be easy, and yet it takes only a few minutes if the machining operation were done right: the neck needs to be 1/8 or so out of the slot when machined, and the angle of the neck to the body needs to have been establish before any machine is done. It is crucial that the neck block itself in square to the centerline of the guitar, and that a straight edge lies flat on the sides (at the block) in line with the heel as fitting the heel to that surface is much easier if it is straight.

The first thing I do after making sure that all the preceding actually happen, is to relieve the male dovetail so that the only remains machined parts are 5/16 along the length of the dovetail, and 1/16" along the edge of the heel. I use a very sharp chisel to do this. Needless to say, I hope, the heel must have been completed before this point. The neck and the body only need to touch on these spots.

Sketch, such as it is:

Image

The relief in the dovetail itself also allows the dovetail to work if skew in altered more than a little. Recall that the neck is a 14 degree bit and the body is a 13 degree bit for the same reason.

First i work the heel shoulders to achieve a good fit, and altering skew as necessary. I use a sharp chisel and a sanding stick for this. It take surprisingly little material to make the required differences.

As machined:

Image

Relieved on the heel face:

Image

relief of the dovetail cheeks:

Image

The 1/16" ledge on the heel:

Image

Once the heel fit the sides, the the dovetail cheeks can be worked to make sure the fingerboard land flat on the top, and the male/female dovetail closes smoothly with mild clamping pressure. When the glue is put in (HHG) it will lubricate the wood and it will close slightly more easily. It is something you get a feel for after a few.

My apologies for the poor focus, I rarely try to take such close pics.

I do not feel I explained this so well as I hoped, so please ask questions and I, or others, will answer them.
Author:  James Orr [ Thu May 28, 2020 9:35 pm ]
Post subject:  Re: Demystifying the Dovetail.
meddlingfool wrote:
What is important is that the gap should be accessible beneath the first fret after the body join so the steam needle can get in there to undo the joint when it comes to neck reset time.


That makes . . . total sense. Thank you!

Bruce Sexauer wrote:
As i happens, my neck block is usually 2 3/4 x 1 1/2. The dimensions of the Dovetail are constrained by function, but within those parameters, there are many possibilities. My dovetail dimensions are what I though would be ideal, and are only conceptually rooted in tradition.


Thanks, Bruce!
Author:  SteveSmith [ Fri May 29, 2020 7:12 am ]
Post subject:  Re: Demystifying the Dovetail.
Explanation made sense. Even though I also use dovetails I am enjoying seeing your very common-sense approach.
Author:  Bruce Sexauer [ Fri May 29, 2020 12:00 pm ]
Post subject:  Re: Demystifying the Dovetail.
The basketball needle method for steaming the dovetail ala Martin was not part of the thinking behind the joint. It was come up with much later by thinking repair techs.
Author:  PatrickW [ Sun Jul 26, 2020 6:41 pm ]
Post subject:  Re: Demystifying the Dovetail.
Bruce your trimming to fit post allowed me to see why I struggle with this part of my builds, the cheeks of my heels are closer to 1/4”. Trimming to no more than an 1/8”, I will reduce my mating surface area by 50%. Thus, reducing my time fine tuning the neck to the body. Thanks for the great post!
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