Acoustic build, neck angle question

[Tweaker]

To you acoustic builders on here, do you incorporate a neck plane into the soundboard (similar to building a Les Paul)? I've been getting my feet wet with acoustic guitar building and am exploring a few different neck attachment methods but I keep running into the same problem. I'm not brave enough to dovetail a neck yet, so I'm working with bolts and threaded inserts for now. (Don't laugh)

With the strings 1/2" above the soundboard at the bridge, the neck is going to require an angle to keep the action correct. But what I'm finding when I try to add a neck angle is that the end of the fretboard raises up above the soundboard. I've only thought of a few solutions to this and I don't like any of them.

First, just glue the fretboard extension to the top. I hate this idea, as it seems like it would stress the fretboard and obviously destroy the flat fretboard plane.

Second, build a taper into the fretboard so the neck sits 90 degrees to the body, and the effective neck angle is built into the fretboard. I don't like this idea because it sounds painful to execute, and in my opinion, look terrible.

Third, build a neck plane into the neck block. I'm not sure I like this or not, as I can't find anything that suggests this is a common solution. I don't like the idea of putting the soundboard through that additional stress. (I realize on the back, the radius can be "forced" so to speak, but there aren't really any direct forces pulling at the back.)

I suppose another option is to build the neck angle into the vertical member of the neck block, so it isn't a true 90 degrees. But that would pull the sides out of square with the top..

What am I missing??

 

[nuance97]

I’ve never built an acoustic, but it’s my understanding that there is a slight neck angle…something between 1° and 2° depending on build specs. So yeah the neck block will have a slight corresponding angle.

 

[nuance97]

And you are aware that the top is radiused right? Usually something between a 40’ and a 20’ radius. That plus the height of the bridge necessitates an angle

 

[cmjohnson]

Go look at some good acoustic guitars and see how they are built. By careful observation you will be able to find your own answers.

When I built my first acoustic guitar, I really jumped out of the frying pan into the fire. Rather than mess around with anything that would be a REASONABLE first acoustic guitar project, I started by building an 18" width (across the lower bout) acoustic archtop, in the same class as a Gibson Super 400. It was a year's project, start to finish. That guitar is now 21 years old and stable and solid as the day it was made. I learned from Bob Benedetto's book, "Making an Archtop Guitar". But his book is centered around building a 17" guitar. I had to start from REAL scratch, drawing out my body model on a big piece of paper and adjusting it until I liked what I saw. Then I built the body form for it, and began building the guitar inside that form.

If I was able to pull off a really nicely made archtop on my first ever try at any kind of acoustic guitar, I'm sure beyond a doubt that you can build an acoustic with a dovetailed and set neck. You just have to do the preparation and planning. This requires you to know what you need to do. Examine guitars that are like what you want to make. Learn everything there is to learn about them. And in doing so, the plans that are in your head will become more detailed and more complete.

 

[nuance97]

I wouldn’t sweat a dovetail. A bolt-on mortise & tenon is a great joint, and many high end acoustics are built that way

 

[Tweaker]

I understand most builders use a radius on the top, while others don't, which certainly adds to the neck angle confusion. I know there are reports of Olson acoustics with a truly flat top (yes, most flat tops are actually slightly radiused).

As I'm still learning what works for me, I'm doing truly flat tops. But out of curiosity, I modeled up a 30ft top radius in CAD to see what the approximate angle is. So assuming a 30ft radius, and a bridge location roughly 11.5" back from the front of the guitar body, that plane lands around the 0.7 degrees. So I can see how sanding that into the neck block would aid in the neck angle dilemma. If we assume a 1/2" string height above the top at the bridge, and a 1/4" thick fretboard with a little extra to account for fret height and action height, you'd need approximately a 1.7 degree neck angle.

So ultimately, I guess it really wouldn't stress the soundboard too much to sand that extra neck angle into the neck block and "force" the soundboard into that plane. At that point the fretboard would sit flush on the top, or at least have a very minimal gap above the soundboard. Small enough that it could be glued down and it wouldn't create an issue with the fretboard.



Regarding dovetail vs. bolt-on mortise and tenon...if bolts work for Taylor, it works for me. The neck angle question is far more pressing for me, and I think incorporating a radiused top would sort out the fretboard gapping issue.

I just need to figure out how to make it work on the true flat top I'm working on right now. The best solution is probably to bring the bridge and saddle down a little bit and possibly deal with higher action in the upper register.

 

[LtDave32]

Just as an aside, there is a ton of great acoustic build information on Luthier's Mercantile.

Tutorial and Product Videos – Luthiers Mercantile International, Inc.

www.lmii.com

 

[nuance97]

From what I’ve seen builders radius the lower 2/3 of the sides (in a radius dish) to accept the top, but the upper 1/3 is sanded flat at the angle of the neck

 

[Tweaker]

Well shoot that makes too much sense. I was too focused on the neck angle, I didn't even think about radiusing the lower section only.

That has to be the best way to handle this for sure.

 

[Joe Desperado]

I’ve built quite a few. I always use a 25’ top radius. The braces match. The traverse brace near the sound hole fingerboard joint is basically flat. The rest are domed.

Modern guitar builders are no longer doing dovetail or mortise joints. They almost all use a butt joint and bolts.

you must angle the end of the neck to make it work. With a butt joint this can be done on the miter saw. If you build the body first, they trying different neck angles is quite easy. Cut your angle on a piece of scrap and see where the plane ends up over the bridge. Essentially you want the top of the fingerboard and the top of the bridge to be in plane with each other. The height of the saddle should be the height of thr string.

 

[Tweaker]

Do you use the 25’ radius as the neck plane or do you sand in a flat section on the sides and neck block to achieve a neck plane?

According to my CAD drawing, the 25’ radius curvature differs from a flat neck plane by about 0.01”. Seems like that’s a tolerance that could be clamped and glued out.

 

[Joe Desperado]

If you use a flat traverse brace (the one right in front of the fingerboard but before the sound hole) , it will be flat flat for the fingerboard to mount. That has never been an issue on any of my builds.

 

[Joe Desperado]

Yeah, .01” is nothing.

 

[Tweaker]

Sounds like on the next build I'm using a 25' radius on the top.

 

[Marty M.]

The first guitar I built was a 000 sized paduak steel string under the guidance of Charles Fox and George Morris. I didn't know anything about scale length or tone woods. I chose Paduak for the look. Most of all the other students were building Rosewood D sized guitars. I'd venture to guess that I'm the only one still building guitars..... We built in the Spanish style which has an integrated foot and heel attached to the sides and back. Tops were flat ( not radiused like some builders do today) and neck angle was/is determined by putting the neck at a slight angle while sanding the foot and linings prior to attaching the back. Fast Forward a few decades. I started to build acoustics again after a couple decade hiatus. I opted for mortise and tenon construction. On these I cut the mortise in the neck block at a 90 degree angle to the joint. The tenon end is cut at a .5 to 1 degree angle on my chop saw. Then I use a router table to create the tenon by cross cutting along a fence, so the joint is at a slight angle to the neck block. Doing it this way , the fretboard has some fall away while remaining the same thickness. Oddly enough I purchased a couple martin necks which were seconds years ago. I just used a couple and found that they did the same thing. Necks are at an angle to their neck blocks. The business of a radiused top is "newer" methodology. I've seen a Blues Creek Video where he radiused the top and then leveled a neck plane into it. I may try that sometime. I just started using a radius disk on the backs on the last couple guitars and that is easy enough. Here is one of my parlors with that angled tenon.

So 15 steel strings and one classical later, and hundreds of electric guitars, I'm happy experimenting with non traditional and more sustainable "tone" woods, bracing, scale length, and pretty much deviating from the norm. All resulting guitars have sounded like guitars and played nicely like guitars.

 

[nuance97]

https://www.harvestmoonguitars.com/kennethmichaelguitars/neckangle.html?mibextid=Zxz2cZ

 

[Tweaker]

Lots of really helpful information here, thanks everyone. That harvest moon guitars article is very in depth, and I like how they simplify it at the very end with the Martin factory technique. Looks pretty easy to incorporate into any build!

Of course, this all assumes the traditional 1/2" string height at the bridge. I suppose you could go closer to 3/8" and not necessarily need a neck angle, but the internet would tell you that you're not getting the correct pressure on the bridge into the soundboard.

Lots of variables at play! Like you said @Marty M. the guitars I've built have come out playing and sounding like guitars, so maybe its ok if some of the variables break away from tradition.

 

[Marty M.]

Lots of really helpful information here, thanks everyone. That harvest moon guitars article is very in depth, and I like how they simplify it at the very end with the Martin factory technique. Looks pretty easy to incorporate into any build!

Of course, this all assumes the traditional 1/2" string height at the bridge. I suppose you could go closer to 3/8" and not necessarily need a neck angle, but the internet would tell you that you're not getting the correct pressure on the bridge into the soundboard.

Lots of variables at play! Like you said @Marty M. the guitars I've built have come out playing and sounding like guitars, so maybe its ok if some of the variables break away from tradition.

I don't think I'd ever really deviate too far from what is generally accepted, but generating some alternatives and trying them out result in instruments that have worked fine. The internet has reinforced the " cookie cutter" syndrome where you have to do the same thing as everyone else. The lack of experience in woodworking ,as shop classes disappeared 30 years ago, only reinforces the idea that one should do something tried and true. This of course results in a lot of tear out to be repaired...LOL.

 

[Tweaker]

I don't think I'd ever really deviate too far from what is generally accepted, but generating some alternatives and trying them out result in instruments that have worked fine. The internet has reinforced the " cookie cutter" syndrome where you have to do the same thing as everyone else. The lack of experience in woodworking ,as shop classes disappeared 30 years ago, only reinforces the idea that one should do something tried and true. This of course results in a lot of tear out to be repaired...LOL.

There are a few traditions I’m comfortable with breaking away from…the rest I generally agree with. Things like not using a hardwood top, for example. The build I’m working on right now has a hardwood top and maybe it’ll sound good, maybe it won’t. It’s worth the experiment in my opinion! I’m betting it will sound like a guitar

I also want to make a flatsawn hardwood top and try to make it explode. Finding limits is part of the fun for me!

 

[cmjohnson]

Uh, spruce isn't exactly a hardwood, just FYI. It's also extremely common in various species and is not endangered or even threatened. Pines, Cedars, Spruces, and Firs are all in the same family Pinaceae and they all make suitable guitar tops. You can argue until you're blue in the face about the subtle tonal characteristics of Englemann vs. Sitka vs. European Spruce strains, but really you can make a good guitar with most ANYTHING in the Pinaceae family. Just pick out some quality pieces with good ring structure, split and selected for proper orientation, and start making parts.

As for hardwood tops, they've been done. Maple laminate tops are common on archtops.

Taylor Guitars has managed to show us, by making guitars that are structurally the same model, out of different wood choices, and that still end up sounding the same, that the acoustic considerations of the wood are probably not as tonally significant as the physical design of the guitar, its parts, its bracing, and its construction.