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So I'm about to close up the box on a commission, which I probably have no right to be selling guitars while still asking questions like this, but here it goes. I built this one in accordance with Cumpiano's book. So the top is glued to the sides and blocks on the workboard, and I'm about to glue on the back. It's a bolt on neck and the heel is roughly carved, nuts and bolts inserted etc. So when I'm test fitting my neck, the neck angle where the fingerboard meets the body leaves the fingerboard extended about 1/16th high over the top at the soundhole. There's no radius on the rim, but it is probably more cylindrical, with it being a pretty straight shot from headblock to tail block. My question being what do I do about this 1.5 degree neck angle where the fingerboard extends over the body. Make a tapered shim? Thanks for any advice in advance.

Mitch

There's about a dozen ways to do this, and most of them depend on working out the geometry beforehand. If I remember Cumpiano's method correctly, you need to sand the top to match the fingerboard, which means taking off 1/16" at the edge and setting the neck 1/16" lower.
The other solution is to make a tapered shim to fit between the top and fingerboard.
What's the height of the strings over the soundboard at the bridge? That needs to be between 7/16" and 9/16", and may help you decide whether you need to sand the top or make a shim.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

Can you attach a picture?

1/16th is a bit steep and I would consider shimming that. You could make up the difference by removing top material for half of that and then just accept a little fall away. You could also fret the guitar after it is finished and bolted on and plane out any hump.

Right now everything is pretty rough. I double checked my current height at the bridge and it's still probably 3/16ths too high, so the numbers I mentioned will come down fair amount. What number do you all shoot for without the fingerboard at the bridge. Seems it might be easier to at least get in the ball park before I glue on the fingerboard and fret. When I checked it now, I just held on the fingerboard and straight edge and placed my bridge.. Is an 1/8th inch at the bridge without fingerboard/frets in the ballpark at the bridge location? (from the top without bridge). I may have less to worry about than I thought since it still needs to come down a bit. Thanks for the suggestions so far!

Here is the way I would look at your situation .... what is the height over the top at the bridge, when the current fingerboard is placed flat on the top where in its proper position and be glued down ??? if you get somewhere around .350, then you are good. Much more than 30 or 40 thou either way and you have an issue. If its shooting way too low (ie your measurement is .300 or under) then you have to set the neck back such that you require a tapered shim under the fingerboard until you get to around .350. If the measurement is high, then you need to pitch the neck forward, and taper the end of the fingerboard where it sits on the top, thicker at the neck joint, to thinner at the soundhole, again, shooting for about .350 of an inch. Within the 30-40 thou window, you can simply sand a taper into the fingerboard form one end or the other depepnding on whether it needs to go up or down. You can also change the neck set slightly, again either forward or back, and then reflatten the fingerboard (setting it forward will give a slight rise to the FB end, and setting it back will leave a hump at the neck joint)

I use a 28ft radius top .. I dont flatten the UTB at all - this geometry almost always gets me right on without a wedge or taper .... I measure the neck angle once the top is on with a sliding bevel, and then use that to set the mitre gauge on the table saw and cut the neck angle on the neck blank - I dont give a hoot what the angle really is, whether its a half degree, or 2 degrees - all that matters to me is that I get about .350 - .370 at the bridge area when shooting a straight edge of the unfretted fingerbaord. How you can cut the neck angle without measuring what you really need from the actual guitar body is beyond me, which is why the neck NEVER gets cut until the body is together.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Thanks Tony and Todd! I actually just got a couple radius dishes in the mail yesterday, and will be changing my construction process a bit from here on out. Thanks for the numbers Todd. I still might be ok here, and I'll take a look at that tutorial in the event that I need the shim.

For this particular instrument, if you haven't fixed it already, it sounds like you need a sturdier workboard shim with no cork and the new style foot.

If you build according to the book (which hasn't been updated in a while) the possibility strongly exists that you will inadvertently tighten things down and ruin the neck angle, unless you are very careful. It's a crapshoot, really, unless you've done it that way a few times and have the right feel for it. Also, the way he cuts the cheeks back before carving the heel creates extra neck angle, you may need to chisel/floss that out.

If you haven't glued the back on, you can still work the neck block geometry into the correct position.

This hardboard shim will support the neckblock without flexing, I've filed the correct angle into it, and this updated shoe will butt up against the neck block (screwed to it through the bolt holes) and will hold the neck sturdily at the the correct angle without moving while the sides and back are attach. If the sides are attached you can still adjust the neck angle.

This is actually kinda like slip setting a Spanish style integrated block/heel to reset the angle, except you haven't completed the instrument yet.

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Old growth, shmold growth!

Glue the back on and then ask your questions.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

I might add keep and eye on humidity when gluing the braces on in the radius dish....

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MK5acoustics.com

Well, right now there's some flexibility to set the neck angle and get it right before he closes the back (unless he's already closed it). Then he wouldn't have to make a shim for the fretboard or end up with a too thick bridge or too tall saddle.

Once the back's on, that's it.

The idea with this build method is to get a straight line from the nut to the saddle with no falloff.

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Old growth, shmold growth!

If he's talking about having to make a 1.5 degree fingerboard shim, something is definitely off. These plans are supposed to end up with a straight neck with no falloff from the nut to the end of the fretboard. With this design, the neck block should be 90 degrees as should the neck heel, and the upper face brace should be curved so that as it's glued, down the area where the fretboard is glued to the soundboard tips back. The 90 degree neck block is orthogonal to the fretboard radius. No shim should be necessary.

It's possible that with the guitar off the workboard the rims are flexing so that the neck angle appears off but whent the soundboard is clamped to the workboard everything goes back where it should, but with the way things are described in the book with no support for the neck block and cork everywhere, it would be easy to get things askew without having done it a lot.

The changes I reccomended are what Cumpiano showed me in his current build technique, and should ensure proper geometry if he followed the rest of the specs in regards to bracing.

If not, a little correction before closing the box means less flossing/shimming afterwards, and a cleaner overall build, IMO, especially since it's a commission, it should be as clean and accurate as possible all around.

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Old growth, shmold growth!