Neck geometry question for semi?

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Neck geometry question for semi?

Postby Randolph Rhett » Sun Feb 03, 2019 1:56 pm

I am interested in making for myself a semi- hollow archtop guitar guitar. Unfortunately I don't have one myself to study, so I'm having some issues understanding the neck geometry.

On a traditional full hollow archtop, like an L5, the neck comes to the body at 4-5° and is elevated off the body about .5". The arch rises roughly .75" off the rims, and the bridge is in the range of 1" tall. All this combines to give you proper action in a reasonable range of adjustment.

On the semi I note that the fretboard is not elevated off the rim, or at best has a .125" shim. The bridge still seems to be the same 1" tall. So something has to give. If I am right about the bridge then the neck and body need to be at a greater angle or the arch has to rise much less.

Can anyone experienced in building 335-ish instruments help me out? What are the rough dimensions that make this all work?

Thanks!
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Re: Neck geometry question for semi?

Postby Bill Raymond » Sun Feb 03, 2019 5:35 pm

Not having built a "335-ish" instrument, I don't know for sure, but from what you have stated and what I have observed I should think that the arch in the 335 is perhaps not as pronounced as in a full-bodied acoustic archtop, and that the arch approaches the neck at a slope that matches the correct neck angle so that the fretboard can lie flat against the top. In addition, the bridge, as I recall, is not as tall as on an acoustic archtop. I'm sure others more experienced with this instrument will chime in.
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Re: Neck geometry question for semi?

Postby Randolph Rhett » Sun Feb 03, 2019 6:17 pm

Well according to one Gibson fan site the ES 335 (in fact the entire thinline ES line) specs 4° to the body. According to Stew Mac, and ABR-1 bridge is roughly half an inch thick and has roughly half an inch of travel. If both are true, the only thing left that can give is the height of the arch. Is it possible that an ES 335 rises only about .25" from the rims? Anyone with measurements out there?

Thanks,
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Re: Neck geometry question for semi?

Postby Bill Raymond » Sun Feb 03, 2019 11:40 pm

Randolph, look here: http://www.upnorthstrings.com/es335body.pdf On pages 23 to about 26 you can see how the top slopes at the neck so that the fretboard will lie flat on the top at the correct neck angle. As I recall from prior discussions here, the top doesn't have quite as pronounced arch as an acoustic archtop, but I don't remember the exact height of the arch. You could obtain Jamie Unden's plan to work from. Sorry I can't be more helpful, but the ES335 is not an instrument that is of particular interest to me, so I haven't studied it carefully.
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Re: Neck geometry question for semi?

Postby Randolph Rhett » Mon Feb 04, 2019 12:07 am

Thanks Bill. That was helpful. I've cross reference a couple of plans to try to get all the dimensions. Looking carefully I see that all the dimensions are cheated to make up for the missing .5". The arch rises above the rims .5, instead of .75, giving you half of the difference. The other half is in the bridge. All the way slammed down it is only .5" compared to the 1" of the traditional wood bridge. There is enough room in there to account for the bottom of the fingerboard being level with the body.

So I guess that is my answer. I'm not building a copy, so I'll just have to give it a good think to see what I want to do. I already have molds for the plates, so I'm reluctant to remake them. I will probably just make the fingerboard .25" proud of the body. I guess I'll have to spend some QT with Fusion 360. :(
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Re: Neck geometry question for semi?

Postby Barry Daniels » Mon Feb 04, 2019 10:50 am

The fretboard should be a little bit higher off the body. My son is building a Stew Mac 335 kit currently and the fingerboard is about 1/2" off the body with a fairly steep angle.

Let me know if you need any measurements.
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Re: Neck geometry question for semi?

Postby Freeman Keller » Mon Feb 04, 2019 8:24 pm

Randolph, I have built two 335 clones and an L5 sort of thing so I have some familiarity with the geometry. Basically they don't have any overstand (my L5 ended up with a small wedge under the f/b extension) but the 335's have approximately the same neck angle 3-1/2 to 4 degrees as a Les Paul. It really depends on how tall the arching is on your top plate (which opens a whole 'nother conversation). Ultimately when you decide on your arching and choice of bridge (and whether you want overstand or not) that will establish the angle. My goal on every guitar I build is to have the fretboard plane just hit the top of the saddles at their lowest setting. That always gives me enough adjustment to get playable action.

I'm away from home until tomorrow night - I can forward some pictures when I get back. Also I used the ALS plans which I feel are close enough for the body size, shape and arching, but were totally wrong for the internal construction if you want to build it like Giibson does.
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Re: Neck geometry question for semi?

Postby Freeman Keller » Tue Feb 05, 2019 8:55 pm

OK, Randolph, I am home and I got out the ALS plans. I built my first 335 to them, then decided to change some things on my second. The ALS plans call out a 2 degree neck angle and show no overstand. Measuring the distance from the top of the binding to the top of the center of the top on the side view gives the arching at 1/8 inch. Interestingly, they also show the height of the binding as 1/8 rather than the usual 1/4. They show a ToM bridge that appears to be sitting on the top of the guitar (ie at its very lowest adjustment). The Nashville style bridge that I use is about 5/8 at its lowest setting.

Anyway, I did initially set the neck at the 2 degrees which seems to have worked with the arching in my top

IMG_2402.JPG


IMG_2467.JPG


IMG_2468.JPG


IMG_2519.JPG


In that last picture the bridge is sitting on little pieces of wood that are the same thickness as the tops of the studs. What I am looking for at that point of construction (since the board isn't fretted yet) is that the end of the straightedge be twenty or so thousands below the tops of the saddles. When fretted I like it to just hit the tops.

Its interesting that when I built the second one with plates from the same source that I have a photo showing the neck pocket jig and my protractor sitting next to it. The protractor reads 3.3 degrees which is very close to a Les Paul. However that guitar did use a roller style ToM and probably was taller.

Bottom line, lay out YOUR neck geometry with both the top and bridge that you plan to use. Decide what range of adjustment you feel is necessary to get the action you like. Hope this helps.
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Re: Neck geometry question for semi?

Postby Randolph Rhett » Wed Feb 06, 2019 12:37 pm

Thank you Freeman. 1/8” of arch is surprisingly little. On a couple of plans I found online, 1/2” seems more common. In any case, I have my answer. All the dimensions that make up the neck geometry are tweaked and not standard to Gibson arch top guitars despite some visual similarity. I’ve spent some time laying it out in CAD, so I guess it’s time to start cutting.
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Re: Neck geometry question for semi?

Postby Keith Howell » Sun Feb 10, 2019 4:46 am

Thank you Freeman. 1/8” of arch is surprisingly little. On a couple of plans I found online, 1/2” seems more common. In any case, I have my answer. All the dimensions that make up the neck geometry are tweaked and not standard to Gibson arch top guitars despite some visual similarity. I’ve spent some time laying it out in CAD, so I guess it’s time to start cutting.


I have a ES330 clone which I am restoring. It has a 12mm arch (1/2 inch) arch top and back.
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