Official Luthiers Forum!

Have you decided how you're going to do the dome on the top and back? I've looked at the photos in AL again, and I believe the Larson bros version has cylindrical top and back, hence the tighter radius. I've done a couple like that, it's a relatively easy method. All you have to make is a couple of 3/4" wide cauls with the desired radius cut on one side.

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

Thanks, Rodger. I'm in the midst of sorting out a method/approach. I was wondering how you determined that? I am confused by the plans, which seem to be missing important details. The plan shows a line (in green) that appears to be dome-like vs cylindrical. Does the pull of the strings pull up on a cylindrical top giving it a dome-ish appearance?

I've been following your posts, both here and other forums. I usually develop my own plans, my construction method requires that I have precise templates for the sides, which are not always included in a plan. I develop these templates based on the geometry I'm using for the top and back, it's a 3D geometry problem that I solve mathematically/graphicly (I'm an engineer with a pretty decent background in CAD). I've gone through what you're looking at for several different plans.
Looking at the plans in the magazine(and the photos of the guitar), it's not at all clear what the top or back geometry is supposed to be. Usually, plans include a section along the centerline of the guitar that shows the longitudinal geometry of the top and back, these plans have the green line that's virtually meaningless, especially on the back. It's pretty clear in the photos that the back does not have a uniform curve as is shown on the plans, and there's no force distorting it. The top is another story, the shape of the top is not that clear in the photos, and as you noted, the strings do pull some arch into the top, which could be the green line.
That's what makes this a bit tricky, the amount the top will deflect under string tension is an unknown and has to be estimated. That estimated value is used to determine the appropriate neck angle to obtain the correct height of the strings above the soundboard at the bridge, which is a critical dimension.
I believe you are interested in building a similiar instrument, not a replica. It's impossible to replicate an instrument from plans and photos, the best you can hope for is getting the geometry close. You'd need some acoustic measurements from the original to replicate the sound. Since you've done the bird's beak headstock joint, I'm assuming you're planning on a dovetail neck joint. That's a bad idea on a first guitar, but I think you've got the ability to get it right if you really want to go that way. I bring this up now because it interacts with the top geometry, and adjusting the neck angle is more difficult with a dovetail joint. Taylor uses a simple bolted on butt joint, which is the easiest. I prefer a bolted mortise and tenion, but don't have a good reason why.
How closely do you want to replicate the top and back geometry? It's not a spherical surface, so you will not be able to use a radius dish.

As an aside, you've already made some kerfed linings, the original used tentalones.

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

Thanks, Rodger.

You confirmed some of my suspicions and confusion about the plan. You're correct about building a similar instrument. I think more particularly I'm trying to capture the qualities of the box. I am already committed to making a bolted mortise and tenon neck joint as others have also mentioned for a first guitar that it would make setting the neck a bit simpler. Also, I know some great modern builders use it and it doesn't diminish the tonal qualities so far as anyone can really say. What exactly are tentalones? The photos from AL #112 as well as the plan call for kerfed linings. Thank you for keeping an eye out on my progress. That's kind of you.

Tentalones, or dentalones(depending on the source), are small individual blocks. They are traditional technique for classical, not so much for SS. Look at the photos again, particularly on page 35.
I've used tentalones, kerfed lining, reversed kerfed lining, and laminated solid linings. I'd recommend solid laminated linings, that really stiffens up the sides. I use 4 or 5 strips 1/16" thick.

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

This looks really good to me. Have you seen this page?:

http://www.cumpiano.com/Home/Articles/S ... block.html

I've used that attachment system for 9 years. It's a good one but you should reinforce the tenon. There should be stuff in the archives on that.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

About half way down the page it shows two cross-grain slats that get glued to the outsides of the tenon. Is that what you mean?

Yes, that's a good way. I inlay some Maple reinforcing bars because I was all jigged up for a 3/4" tenon and didn't want to change for a narrower one so the external reinforcement could be used.




If I was just starting out I'd do it like the article says. I did some pull out testing without and with reinforcement and there was a big difference.
I also saturate the area around the holes for the hardware with thin CA.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

edit: Mr Kennedy posted while I was typing, I have to agree the pullout strength is an order of magnitude higher with reinforcement.
That's one method, another is to drill a hole vertically through the tenion and glue in a dowel.
Yes, I've seen that link, I think I may have referenced it another thread. I assumed that was what you meant when you said you'd committed to a M&T joint. I've used that joint from the beginning (12 years for acoustics), with no reinforcement. I try to make the tenion a little over an inch, and it's worked fine in the neck woods that I've used. If I had a mahogany tenion, I'd reinforce it. My center laminate is usually maple, purpleheart, or something similiar. I've used mahogany for the outside laminates, I like it as a neck wood. I started with Cumpiano's book, and have altered that method to suit my skills and desires. That's the great thing about being an amateur, you can use one method or another because you enjoy doing it, even though there are quicker and/or easier ways.

As for the top, there are several ways to interpret the plans, they're sort of vague. You have several alternatives.
1) You can build the top completly flat and let string tension pull some arch into the top. Some top builders use this method.
2) You can build the top as a cylinder, with a straight line from the neck to the heel. This is probably close to what the Larsons used, the shape was cut into the workboard they used to glue braces. A brace going diagonally across a cylinder is a complex curve, but's that's not an issue if you glue a flat brace "under tension" to the shape of the workboard. String tension would also pull a little arch into the cylinder, probably a little less than a flat top.
3) You can use a spherical top, probably most widely used. There are a number of ways of slightly distorting the spherical surface to make a flat spot for the end of the fingerboard.
4) Some combination of the above methods

From the photos on pg 29, it looks like the top sinks a little at the waist/soundhole area, and the bridge sits on a bit of a dome. This could have been a flat top when it was built. I'd replicate that as a cylinder by building a workboard. I'd cut an 18' radius in 1x4s spaced 4" to 6" covered with 1/8" masonite.
The back appears to have all the taper between the neck and the waist, with the lower bout more less uniform depth. I'd guess that was planed into the sides prior to glueing on the linings. You should have no trouble doing it that way. Glue the braces to the back in the same workboard as the top, that will give the back a transverse arch. The longitudinal arch will be dictacted by the sides, the back may need to be flexed slightly to make the transition at the waist.

I've been doing this for a while, but I've only built 20 or so, less than half of those acoustic. They have all been different, the only body I've done twice was one nylon and the other SS. I've got some firsthand experience, but there are others on here with much more experience.

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

Thanks Rodger. I know you take time and put effort in to your responses. They are useful to me and I'm glad you are willing to do it. Thx!

Question: I'm not sure I'm understanding the orientation of vertical in regards to the tenon in your statement: "another is to drill a hole vertically through the tenion and glue in a dowel." Do you mean down from the truss rod channel towards the heel cap area?

Thanks for this thread, I'm learning a lot. I know how much effort goes into sharing a build thread, so kudos to you and to all; keep the info coming if you please. Those of us that are about to "get their feet wet, acoustically speaking" really appreciate it!!

Yes, down through the tenion from the truss rod route to the heel cap. That gives some side grain to hold the bolts. I've done several without reinforcement, but I would reinforce mahogany, probably with crossgrain maple strips as shown in the photo.

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

All the bracing is glued in with HHG. I need to clean it up a bit. I don't know if this a fair question or even answerable without actually handling the soundboard... but is there anything glaringly wrong about it at this point? I've been tapping it and shaving down the braces, but honestly other than it sounding very nicely resonant, I can't say I know what else I'm looking for. The Lutz spruce is hovering between 2.7-3.0 mm thick. I've taken into consideration that beginners tend to leave the braces too think. I've also got in mind something I saw in a Somogyi clip about making it so light that it is on the verge of collapsing.

I don't use that pattern so it's tough to comment. Is the bridge plate supposed to be angled and not touching the X according to the plans?

If you are in that 0.114-0.118 ballpark with the top and it sounds musical when you tap, I'd take a chance on what you have. After all it's a first guitar, you need a baseline. You can also voice the closed box by thinning the edges of the lower bout before you bind if it taps a little tight. You will be re-trimming the ends when you shorten them to fit the rimset when closing the box.
Look up Dana Bourgeios' articles on voicing and somewhere along the line check out the Gore/Gilet books. Good stuff.

One tip on hide cleanup, clean up the squeeze out right away when it jells (I use spruce off cuts from braces that are tapered) and stick a toothbrush in your glue pot to scrub the residual off with hot water. Dry with a paper towel and then your heat gun. Gets most of it.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Top thickness is probably OK, bracing looks like the original. You do need to reinforce the rosette on the inside.

How did the top geometry come out?
I doubt there's much longitudinal arch, that's a pretty wide angle on the X, so it doesn't extend the length of the body. On the other hand, there's probably a good transverse arch, there's a lot of crossgrain bracing in this design. You will need to plane the sides to fit the braced top prior to glueing the linings for the top.

Are you going to make an outside mold? It's definitely worth the effort, even for just one.

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

Thanks, Terence. Yes, the baseline is sorely lacking on a first guitar. The top seems very resonant, but I don't know how much I can shave the braces before it looses structural integrity. Glue cleanup was a painful lesson. Very hard and brittle. I have begun to scrap it down which I realize will thin the top a tad more, which I don't think I mind.

Hi Rodger,

The top has a mostly cylindrical arch. I shaped the X-Brace to a 12' radius and then scribed the remaining braces in the lower bouts to that curve. the two UTBs are almost flat. I held a long straightedge down the fretboard that was seated flush in it's future place above the sound hole and saw (with allowing for fret height) that it was about the right height above bridge and saddle (Based on measuring the height of the plans about 10.5mm).

As for the outside mold, yes, I will definitely make one. Thanks again.

[quote="Steven Bollman"]
I held a long straightedge down the fretboard that was seated flush in it's future place above the sound hole and saw (with allowing for fret height) that it was about the right height above bridge and saddle (Based on measuring the height of the plans about 10.5mm).

Did you also have the neck attached, or just the fretboard? Your goal should be to have the strings about 1/2" above the soundboard at the bridge, 10.5mm sounds a little low. Don't forget the top will pull up a little under string tension, as will the neck.

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

No, just the fingerboard. The 10.5mm figure is minus the fret height allowance. I don't think I was clear in how I worded that. I don't have the sides and back together or the neck/fingerboard assembly done, so I just lay the FB on the soundboard. I think (and hope) I'm in a workable range. Also, I will be using a mortise and tenon bolted neck.

You won't be able to tell anything useful until you've got the sides and headblock together, and the neck and top fitted & clamped in place. Then you can clamp the fingerboard in place and check with a straightedge to estimate the height of the strings above the soundboard at the bridge.

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

OK, Thx. I'll report back when I get closer to that step.


The back thickness (Brazilian Rosewood) called for in the plan is mostly running around 2.0-2.2mm (some areas as low as 1.7 and as high as 2.4mm). Is that reasonable? Is it significantly more fragile at that thickness. I have currently hand planed it to a pretty consistent 2.75mm thick. I thought I would take a pause and see if there's any prevailing wisdom about the final thickness. The tap tone is very gong like. Dare I say musical. Thanks.

You could go a little thinner, but what you have is reasonable for a back thickness.

I would go thinner than that on the sides, it will make bending easier.

Stiffness is proportional to the cube of the thickness, so a little less thickness can make a huge difference in bending effort. Thinner sides are not as rigid, but using solid laminated linings more than makes up the difference. Rigid sides really only helps during the building process, once the top and back are glued on nothing is going to move anyway.

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

Thx, Rodger. I reduced the thickness to an average of 2.50mm. Feels good and sounds goos as best I can tell without having a baseline to judge it by. I'm very curious to finally strum the thing to see if my gut feeling on tap tones matches up with reality.

Even though I haven't posted lately, I have been busy working away on the guitar. Here I am thicknessing (thinning) the back plate.



Here's what the back plate looks like with the braces glued on but not yet shaped.


These handy tools are good for radiusing the edges of the braces.


Shaped braces. Still some fine tuning to do...


Outtards


Innards