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As far as neck angle is concerned I simply angled the upper bout down a little bit from the head block through the middle of the sound hole. I didn't even measure it, just did it by feel and by looking at how much of the linings were taken away. There is a tiny bit of fall away and plenty of saddle height for future correction.

Steve,

Give Matt Mustapick an e-mail - here's some pictures from his website of the bracing on a multi-scale baritone he's making, I don't know what doming of his tops, if any, that he uses. I've made quite a few multi-scale guitars and have just started a multi-scale baritone harp guitar, and all of these with my usual 13' top radiused braces. I think the degree of top doming you are pondering will be the least of your worries, 25' - that's flat isn't it

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Steve : Bruce Sexauer builds compound scale guitars.Not sure if he uses a doom or flat top. You should be able to catch him at the UMGF.Think I read somewhere that Jean Larrivee takes a different approach on his guitars. The main bout is built flat and the upper bout has a doom. He claims that the string tension will then raise the main bout a bit and lower the upper bout a bit. h
He says this works better and looks better. Maybe some ex employees can jump in and comment.
Tom

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Somedays I say it's to enhance bass on smaller guitars......other days I say it's for more balanced tone on Dreads and Jumbos. I experimented some a few years ago with the same guitar, even the same top, just different braces. The flat version was more boomy. For me small bodies can use more "boom" but dreads and jumbos have enough already. I use flat rims on all of them.... or actually




Yep, I just didn't do a good job explaining. I use flat rims......or actually faceted rims either way. I aim a straight edge from the neck block to the bridge location and slope the rims to make the neck angle work out. On radiused tops I also figure the rise into my angle. My method works great for me, but there's other, probably easier ways to work it all out. I believe, when using a flat top humidity control is REALLY important when gluing things up.

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Many thanks guys!
Meddlingfool, I DO believe you are correct sir about the doming...don't know what I was thinking....
Out the door right now for a LINT meeting, but I'll check back when I can.
Again, thanks.

Steve

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From Nacogdoches...the oldest town in Texas.

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I was actually thinking about this for my next build. Does he arch the upper part of the x brace only? Does he arch the upper transverse brace?

I suspect Bruce would be happy to answer your questions. http://www.sexauerluthier.com/

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jfmckenna: Not sure exactly what he does. Just recalling this from an article a read quite a while ago. Sorry about that. You might try to make contact with him or one of the ex employees. Think some of the folks who post here have worked for Jean. Good luck.
Tom

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Great discussion! I certainly don't mind when the same old topics are brought up again. Seems like I learn some new things every time.

One thing I've been pondering lately is the effect of mass in the top. Seems to me that more dome = more stiffness, thus you can thin the top further and reduce mass. But maybe you don't want to reduce mass too far. Or maybe you do want the plate itself feather light, if you make a more massive bridge to give the top as a whole some more inertia for pumping low frequencies? I'm not sure.

But basically, I'm thinking varying the dome based on top species/stiffness to weight ratio might be a good idea. Something light and stiff like spruce or redwood might be better closer to flat (although redwood I'd worry more about humidity cracks), but something heavy like mahogany or koa would likely do better being thinned further to reduce mass, and pulled to a dome to make up the stiffness. I'm currently building a "test body" to try out different tops on, to hopefully verify some of this stuff. Anyone have experience with flat versus domed on hardwoods?

westca, I'm curious about your comment on the dome not stiffening behind the bridge. What makes you think that? My instinct is that flat would be the weakest point between a highly curved dome and a dished in, inverted dome. It does seem like the apex where the bridge is pushing down into the top would be even more stiffened by the dome than the area behind though.

The X intersection seems like one of the trickiest areas to get the stiffness right, especially since you can't shave and tap and feel to judge the effects, since you'd have to glue on a new cap every time you decrease the height at all. Hard to judge exactly how much lower you'd want it on a dome top versus flat top.

I rather like the Cumpiano&Natelson book style of springing the top onto the braces with cam clamps, and gluing flat rims onto that. Easy to construct without dishes or molds, and geometry works out nicely with a flat run under the fingerboard when the neck is angled for 1/2" string height with a 3/8" thick bridge. My recently completed first guitar has a 1/8" arch offset on the X braces. Not sure what that translates to in feet radius. Upper transverse brace is flat under the fingerboard, but then arches down 1/16" to the rims, so over about a 3.5" distance from the 14th fret to UTB, the 1/16" rise produces a 1-1.5 degree angle for the fingerboard extension to lay on.

Alexandru, have you built any flat tops with zero neck angle? Seems like most people here are cutting the neck angle into the rims. You might be able to get away with no angle if you increase the fingerboard thickness though. Assuming you want approximately 3/8" + 1/32" straightedge projection at the bridge, then with frets being 0.043", you need a fingerboard thickness of about .363", or 0.113" thicker than the usual 1/4". So to get to a total 1" thick neck including the frets, you get 0.594" of shaft, which leaves more than the recommended 1/8" of thickness after a .4" deep truss rod slot for an Allied rod or 7/16" StewMac rod.

Alternatively, you could get some neck angle by cutting it into the fingerboard, so the neck shaft through bridge is all flat, but the fingerboard is thinner at the nut end and thus projects the strings higher above the bridge. I like the neck as a whole to be a little thinner at the nut and thicker at the heel anyway, so having a constant shaft thickness and a tapered fingerboard would be effectively the same.

Oh, and fan frets... that Mustapick baritone bracing is quite interesting, and the X does match up with what I'd think would be best. Rotate the bass side leg so it crosses the bridge wing despite it being further back, and offset the center toward the treble side where that end of the bridge is closer to the intersection and thus pushing down harder there than the bass side is. And meddlingfool is right, with a radius dish, it doesn't matter where the X intersection is as long as the braces are sanded to the radius and the rims are even.

My next "real" guitar (not the retop tester) will be fan fret, but I was planning on going with the style of twisting the central portion with the saddle and pins, but keeping the wings relatively perpendicular to the centerline so they intersect the X at the usual place, and drive the top in the usual way. Otherwise the primary stiffening direction of the bridge is at an angle and seems like you'd get some significantly different mode patterns. I love the sound of Michael Greenfield's fan frets with fully rotated bridge though, so it is tempting to go that way. But I figure better to go with what seems more natural to me.

No I did not, except for in my twisted mind where I got the math wrong at some point. Such a thick fingerboard would be perfectly ridiculous.

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Build log

I build true flat tops. I just like the building method.

As Todd L mentioned, 1300+ Olson's can't be wrong And actually, he's one of my biggest motivators. I love the sound of Olson guitars. The flat top is just one more part of the system to get the sound you want.

Wood is wood, and if it dries out from it's equilibrium point from when construction happened, it's going to move by either dishing or cracking, regardless of if it's domed or not....

One of the biggest success stories in the guitar making world has to be Bob Taylor. His factory guitars are all built with a 25'R dome, but just a few years ago he launched the R. Taylor custom line where he offers a 60'R dome or a true flat top...chew on that for a while....

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I'm a little late to the party, Steve, but thought I would chime in anyway. I built several guitars with a 28' radius but have used 40' on the last three. It is tough to tell much different in sound due just to the radius as the guitars have been so different, even using different woods for the tops. When building flatter tops, I noticed I really have to keep an eye on humidity. The first one I did with a 40' radius was closed up when the humidity was around 50%. When the humidity over the winter dropped to the mid thirties, the top sunk in. I picked up the guitar and freaked out. I immediately picked up an in case humidifier and got it back in good health, but it was a real lesson on humidity and flat tops. My 28' tops seem to be a much more forgiving. I think if I were building a guitar for someone who likely wouldn't pay much attention to humidity, I'd use a 28' just to build in a little margin. I'm building a claro walnut J-185 now that will be shipped to Utah. I wanted to use 40' radius on the top, so I braced and closed the top with humidity at 40%. The owner will still need to watch the humidity, but I think he is the kind of guy that will.

Sure would be nice to have lots of time to build and test.

Ken

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RH will affect any plates, radiused, arched or flat. It is just more obvious on truly flat tops and larger radii, because they have the potential to cave in.
This is why I never brace above 40% and close the box even drier, around 35%, and often less.
It is the arching across the grain that makes the plate stiffer longitudinally.

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Laurent Brondel
West Paris, Maine - USA
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Domed tops are stiffer and they can take a larger RH swing till they crack. Still there is nothing wrong with a flat top . I do use a 1 1/2 degree neck angle and use the 28 radius to help establish that . Is one better than the other ? I don't think so , it is just different.

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Should this be "can be" stiffer? Depends on the brace height etc.... I know you mean all other things being equal but I had to say it

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Thanks guys, all interesting stuff.

I'll post pics when I take a course of action on this guy.

Steve

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I love the sound of steel strings on true flat tops too... As Woody said -- especially on Small body guitars... which tend to be "Treble" balanced by design already....

Neck angle wise -- I think some people are really over-thinking it.... Line up the neck to body with a straight edge -- just like you normally would... Comes out fine! Mine come out at nearly 0*

Thanks