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Establishing the neck angle
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Author:  dmills [ Thu Sep 28, 2006 11:59 am ]
Post subject: 
I’m working on my first build as noted in a few previous posts and am trying to get my head around the top geometry and its relationship to the side profiling as required to achieve the proper upper bout angle for the neck extension line clearance at the bridge location.

I intend to keep the upper face brace and upper transverse graft flat and radius all other braces. I’ll then bowl sand the rim top in my 25’ radius dish. Based on some of the archive posts (and Finocchio’s video), I should then elevate the lower bout with a 1/8” spacer and sand the upper bout on a flat sanding block to flatten the rim area from the head block to the upper face brace position.

Am I correct in assuming that this will establish the 1.5 degree angle required at the upper bout for the neck set while also allowing the fretboard extension to lay flat upon the sound board? Or - will the 25’ radius + the flat sanding exceed the 1.5 degree angle target?

Whatever the final angle, I assume I should use a sliding bevel to transfer the exact top angle at the upper bout to the neck tendon and trim accordingly.

Am I understanding this correctly? I know there are several slightly different approaches to setting the neck angle.

Thanks in advance for the help.
Author:  dmills [ Thu Sep 28, 2006 2:25 pm ]
Post subject: 
Hesh, Michael -

Thanks for the quick replies. I'm at the point where I am ready to bowl sand my rims and I wanted to be certain that the combination of the 25' bowl sand AND the flat board sanding of the upper bout would not result in overshooting the 1.5 degree target. Sounds like it will not.

Hesh - by re-flossing the heel face cheeks you mean that after trimming the front face of the neck tendon to adjust the neck angle to match the upper bout angle (assuming it's correct), the heel cheeks no longer flush up with the sides and have to be readjusted?

Dougdmills38988.976712963
Author:  phil c-e [ Thu Sep 28, 2006 3:53 pm ]
Post subject: 
doug,
sounds like your planning on dovetailing. i use a butt joint with two threaded inserts, but maybe something i do can still be helpful.
i use a 25' top radius, but all the braces get the radius. i take a little off the bottom of the fingerboard extension to account for the top arch. a few well known builders do this, though i don't think it's a frequently taught method. you may not be comfortable doing that.
but something else i do that you might find useful is to test everything first on a 2x4 (the same length as the neck) on edge. hold your fingerboard extension over the body and find your neck angle with a sliding bevel. transfer that angle to your 2x4. cut that and lay the fingerboard on it to see if everything looks right. any mistake you make costs you penny's.
and once you've done that you can carve up your 2x4 into a handle for finishing.
hope this helps.
phil
Author:  SimonF [ Thu Sep 28, 2006 5:48 pm ]
Post subject: 
Doug,
Here is a solution that works flawlessly for me and yields a neck as true
as Taylor - and you can't do a neck any more perfect than that.

I use a 28" radiused soundboard. If you take a straight edge and lay it on
the upper bout where the fretboard goes, it will give you very close to 1/
16" airspace where you bridge will be placed. If you account for a .250"
thick fretboard plus the fret height, this will give you a perfect neck angle
- where a straightedge set atop your fretboard hits the top of your
bridge. This assumes you are using a 3/8" thick bridge.

In practice, the upper bout is usually never perfect so I take a 1/16" thick
shim and place it at my bridge location. Then I take a long flat workboard
to which I have afixed some 150 grits sandpaper. I move the workboard
back and forth with the end sliding on top of the shim. I stop when the
upper bout has been uniformly sanded. This gives the upper bout the
perfect "ramp" for the perfect neck angle. I use a tenon jig by Craig
Holden that allows you to figure out the matching angle for the tenon -
but you could just as easily figure it out with an angle gauge and cut your
tenon respectively. Then all you have to do is make sure the tenon
cheeks sit perfectly on the sides. Note that you need the headblock
region of the sides to have no ripples but be perfectly flat.

This will ensure that you avoid the dreaded 14th fret hump - which is
generally caused by the tenon angle not matching the upper bout angle.
If you get both of them aligned you won't have a hump.

In reality, especially on your first guitar, it doesn't have to be perfect by
any means to be very playable. This is one of those things that you can
get close enough the first go around and then improve on subsequent
tries.

Best of luck, friend!!!

Simon
SimonF38989.1197453704
Author:  SteveCourtright [ Fri Sep 29, 2006 1:56 am ]
Post subject: 
Doug: sounds like your build is coming along, how about some top and back pics? Mine has slowed down until next paycheck to get some needed tools for that step. Your questions are very useful to all us noobs.
Author:  L. Presnall [ Fri Sep 29, 2006 2:27 am ]
Post subject: 
[QUOTE=SimonF] Doug,
Here is a solution that works flawlessly for me and yields a neck as true
as Taylor - and you can't do a neck any more perfect than that.

I use a 28" radiused soundboard. If you take a straight edge and lay it on
the upper bout where the fretboard goes, it will give you very close to 1/
16" airspace where you bridge will be placed. If you account for a .250"
thick fretboard plus the fret height, this will give you a perfect neck angle
- where a straightedge set atop your fretboard hits the top of your
bridge. This assumes you are using a 3/8" thick bridge.

In practice, the upper bout is usually never perfect so I take a 1/16" thick
shim and place it at my bridge location. Then I take a long flat workboard
to which I have afixed some 150 grits sandpaper. I move the workboard
back and forth with the end sliding on top of the shim. I stop when the
upper bout has been uniformly sanded. This gives the upper bout the
perfect "ramp" for the perfect neck angle. I use a tenon jig by Craig
Holden that allows you to figure out the matching angle for the tenon -
but you could just as easily figure it out with an angle gauge and cut your
tenon respectively. Then all you have to do is make sure the tenon
cheeks sit perfectly on the sides. Note that you need the headblock
region of the sides to have no ripples but be perfectly flat.

This will ensure that you avoid the dreaded 14th fret hump - which is
generally caused by the tenon angle not matching the upper bout angle.
If you get both of them aligned you won't have a hump.

In reality, especially on your first guitar, it doesn't have to be perfect by
any means to be very playable. This is one of those things that you can
get close enough the first go around and then improve on subsequent
tries.

Best of luck, friend!!!

Simon
[/QUOTE]

How about this scenario:

Laying the straight edge on the f/b extension area as you indicate...now the airspace at the intended bridge location is too great...now you'd need to take neck angle away, which will leave a gap at the f/b extension & body joint...(creating a need for a "wedge" under the f/b extension)...will the 1/16" shim and sanding the upper bout trick flatten the area enough to get the proper angle without a "tell" at the upper edge of the soundhole? (ie, getting too thin on the top soundhole edge?).

Larry
Author:  SimonF [ Fri Sep 29, 2006 3:18 am ]
Post subject: 
Larry,
I think part of it depends on your build design and bridge placement...but
for me, the 28" radius gets me "very" close to my preferred 1/16" airspace
at the bridge. I usually end up sanding just enough to flatten the arch
along the centerline at the upper bout - usually just a little bit right above
the rosette. We aren't talking about very much sanding here. Also, with
the headblock and then your upper bout brace - you have a ton of
strength in that area anyway, so I imagine you could sand away for awhile
before there would ever be a hint of a structural problem.

Then if you can cut your tenon at the exact complimentary angle, you end
up with a perfect neck-body joint. This part has to be done perfectly,
which is why I like Craig Holden's jig which is a take on Charles Fox's
design - it work great and is fantastically accurate. Once this is done, all
that is left is making sure the neck aligns with the centerline and the
tenon cheeks are made to fit tightly against the sides. Like with
everything, there are many different ways to get the job done well - but I
have found this to be a really simple and effective method for me. I think
a 25" radiused top would end up giving you too much airspace at the
bridge - you would probably need to flatten the upper bout brace some
to compensate.

--
SimonSimonF38989.5152777778
Author:  Michael Dale Payne [ Fri Sep 29, 2006 4:03 am ]
Post subject: 
I use a 28' radius. I used autocad to determine the apex location and axis tilt so that the dome provides a near 1.5 degree average slope at the lower bout. I don't final level the fret board till it is fitted and final mounted mounted. This leaves me enough material on my fretboard to level to the bridge to fretboard plane relationship I want. Obviously this means I don't fret the fretboard till the neck and fretboard in permanently mounted. I find this leves me room to fix minor errors in the fit up if they should pop up like 14th hump

Here is my SJ dome apex position
MichaelP38989.6076041667
Author:  dmills [ Fri Sep 29, 2006 2:36 pm ]
Post subject: 
Terry,

Your jig seems to provide a very good solution to the problem - directly angling the upper bout rims without resorting to arbitrary shim spacers or reducing the top thickness. One question though. You note that the height of your pivot bar is set at the bridge thickness - but wouldn’t the thickness of the bar be set to the bridge thickness + the additional elevation resulting from the domed top beneath the bridge?

And to everyone else, a big noob thanks for the help and suggestions.

thanks
dmills38989.9871527778
Author:  TonyKarol [ Sat Sep 30, 2006 11:56 pm ]
Post subject: 
I do mine like Michael Payne .. never worked anything out like he did, just discovered that it works once I did it (lucky me). But he is right, the 28 foot radius allows you to just set the neck until the FB lies flat (after a light sand to flatten the top under it), and then you can radius the FB and adjust its slope slightly if needed to get the correct bridge gap. I have never had to shim or taper a fretboard. It works for me.
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