Official Luthiers Forum!
http://w-ww.luthiersforum.com/forum/

How many builders use an A-Frame rather than a Popsicle brac
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=31280		 Page 1 of 1
Author:  CharlieT [ Sat Feb 26, 2011 6:51 pm ]
Post subject:  How many builders use an A-Frame rather than a Popsicle brac
I’m curious how many builders use A-frame bracing in place of the popsicle brace, and why? Is the A-frame more appropriate for some guitars than others? If so, which sizes/shapes benefit from its use?

I’ve also noticed some guitars with neither, and I think I’ve read that that was the norm for many pre-war guitars. I would think that practice would be more appropriate for smaller bodied guitars than, say, a dreadnought, but that’s just an uneducated guess. idunno

The top bracing between the soundhole and the neck block is probably the part of the guitar’s anatomy about which I’ve thought the least, and I’m realizing it’s probably one of the most important from a structural standpoint, so I’d better start thinking about it. duh Any help with that would be appreciated. :mrgreen:

Thanks!
Author:  Ken Franklin [ Sun Feb 27, 2011 12:31 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I generally use a trapezoid shaped 1/8 inch patch which I think helps spread the load and allows me to sand the top flat in that area for the fingerboard extension. Then I don't have to worry that the top being thinner has compromised much strength. It probably adds some.
Author:  DennisK [ Sun Feb 27, 2011 1:33 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I like the L shaped headblock style, butting to the upper transverse brace to lock the shape of that whole triangle of upper transverse to neck joint as tightly as possible. Haven't made up my mind whether that's enough, or a C shaped headblock doing the same thing to the back's upper transverse brace would be worthwhile. Probably is. With big side braces connecting the upper transverse braces to eachother as well. Big 3 dimensional triangle thing, right in the area where a small deformation can make a big difference in string height at the bridge. That way the rest of the box has to deform a lot for it to ever need a reset.

As I understand it, the A-frame essentially serves the same purpose, increasing stiffness of the UTB-to-headblock area to reduce deformation over time. Also has a nice feeling of connectedness when the soundhole braces actually pass under the UTB. But I don't know if I prefer that to maybe get the upper bout moving a touch, or using separate heavy A braces above the UTB, making the UTB as rigid of a wall as possible, and put a little more flex in the soundhole braces where they butt to it so the main active region can pump more easily. That ought to be more or less the same effect as the headblock extension, and a bit lighter weight too.

The popsicle brace just seems silly. It hardly adds any stiffness, so it's pretty much up to the thin soundboard alone to deal with all the stress of the headblock crushing it. Might help a little against cracks, but I've heard plenty suggesting that it's not so great at that either.
Author:  Mark Groza [ Sun Feb 27, 2011 9:38 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I only use a UTB in that area. But my neck blocks are bigger to compensate. It keeps my truss rod which runs just under the soundboard adjustment clear of any obstructions. A popsicle would be in the way on my guitars. My soundhole braces running from the UTB to the X are larger as well. My fretboards are glued to only the tenon, not the soundboard so there's no pressure on the soundboard to crack it in that area.
Author:  CharlieT [ Sun Feb 27, 2011 1:08 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
Thanks guys!

A general question…do you use the same approach regardless of the size of guitar?

Ken – I like the trapezoid idea as it seems to concentrate the benefit of the cross-grain stiffness and crack resistance below the fretboard where it is needed, while freeing up the top out toward the edges. And, as you said, it allows you to flatten the top below the fretboard without concern for weakening the top in that area.

Dennis – wow, lots of great info there! The L and C shaped headblocks are something I had not considered. It seems to address both concerns of crack resistance and neck twisting/shifting without adding undue stiffness to the outer edges of the top in that area. I definitely need to think more about this option. Do you bolt the fretboard to the headblock extension or just glue it to the top? Do you have any photos of your headblock assembly you would be willing to share?

Mark – how much larger do you make your neck block to compensate for no popsicle brace? Not gluing the fretboard to the top is something I had not considered. Do you cantilever it so that the fretboard is not in contact with the top below the neck block? That would free the top to move more in that area, which seems like a good idea from a tonal standpoint, although there appears to be a lot of disagreement on whether there is much, if any, tonal contribution from that posrtion of the top.

Thanks again to everyone for sharing your thoughts and methods! I’m learning a ton here.

Charlie
Author:  Mark Groza [ Sun Feb 27, 2011 2:02 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
Mark – how much larger do you make your neck block to compensate for no popsicle brace? Not gluing the fretboard to the top is something I had not considered. Do you cantilever it so that the fretboard is not in contact with the top below the neck block? That would free the top to move more in that area, which seems like a good idea from a tonal standpoint, although there appears to be a lot of disagreement on whether there is much, if any, tonal contribution from that posrtion of the top.

Thanks again to everyone for sharing your thoughts and methods! I’m learning a ton here.

Charlie[/quote]
Charlie, It depends on the model i'm building My dreads have a 2"+ thick neckblock. But that is because my tenons are longer as well. I don't think the upper bout moves much as far as sound goes.It might vibrate somewhat though. My fretboards don't make any contact with the soundboards but are so close, you would think they are glued by looking at it. My guitars have a true bolt on neck. It can be removed without heat or damage to the soundboard that way. I haven't had to do any resets yet, but if one ever needs one, it can be done easier this way as well.
Author:  woody b [ Sun Feb 27, 2011 3:21 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I used to use L shaped neck blocks, but lately I've been doing mine similar to Kens. I use a thin patch when using a dovetail neck, but make it thicker for bolt ons. On bolt on necks I also bolt down the fingerboard extension. I've considered a complete A frame, and like the design, but haven't used any. What I use works for me. so I'm kinda reluctant to change it. There's more than one way to skin a cat.
Author:  Jimmy Caldwell [ Sun Feb 27, 2011 4:30 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
Ken Franklin wrote:
I generally use a trapezoid shaped 1/8 inch patch which I think helps spread the load and allows me to sand the top flat in that area for the fingerboard extension. Then I don't have to worry that the top being thinner has compromised much strength. It probably adds some.


I do mine the same (unless I'm building a reproduction, then I duplicate the original) except I run the grain parallel with the top grain. I go the idea from a post by John Arnold on the UMGF. I've gotten a lot of good ideas from John Arnold.
Author:  Brian Forbes [ Mon Feb 28, 2011 1:00 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I popsicle a dreadnought and use nothing on a OM cutaway. The head block is massive on the OM, and it covers alot of real estate. I want to give a-frame a try, and I think I will on my next OM without a cutaway. I never liked the upper transverse graft on the guitar soundboard. It seemed like it just replaced all the wood you carefully planed away to thickness the top down. Also, according to one member some guitars intentionally skip the step of using a popsicle, move the whole bracing system toward the neck about an inch, and tweak some brace angles in order to get a louder voice from their guitars. It was a stew-mac article they posted about guitars that were "banjo killers" due to their loudness. Here is the link he was nice enough to share:
http://www.stewmac.com/tradesecrets/promo/ts0051_xbraces
Author:  CharlieT [ Mon Feb 28, 2011 6:41 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
Thanks for the additional info guys.

Jimmy - may I ask what the thinking is behind running the grain of the reinforcement patch parallel to the grain of the top? Seams like running it in the opposite direction (parallel to the UTB) would add more crack resistance and stiffness in that area, but I don't know.

Charlie
Author:  woody b [ Mon Feb 28, 2011 6:52 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
CharlieT wrote:
Thanks for the additional info guys.

Jimmy - may I ask what the thinking is behind running the grain of the reinforcement patch parallel to the grain of the top? Seams like running it in the opposite direction (parallel to the UTB) would add more crack resistance and stiffness in that area, but I don't know.

Charlie


I'm not Jimmy LOL,

Running the patch with the grain the same direction will still offer crack resistance, because the grain lines of the individual pieces won't be exactly in line. (Like using double sides?) A cross grain patch could actually cause cracks, in extremely dry settings. The patch wouldn't contract along the grain, but the top would contract across the grain.

Right Jimmy?
Author:  CharlieT [ Mon Feb 28, 2011 6:59 pm ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
woody b wrote:
I'm not Jimmy LOL,

Running the patch with the grain the same direction will still offer crack resistance, because the grain lines of the individual pieces won't be exactly in line. (Like using double sides?) A cross grain patch could actually cause cracks, in extremely dry settings. The patch wouldn't contract along the grain, but the top would contract across the grain.

Right Jimmy?


Ah ha! Excellent point Woody. Thank you for clarifying that.

Charlie
Author:  John Arnold [ Tue Mar 01, 2011 12:48 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
I use a red spruce trapezoid patch, with the grain running the same direction as the top. Normal thickness is the same as the top....about 1/8". I like the idea of fitting the patch tightly between the neck block and the #1 brace, because it 'scotches' the neck block against any movement toward the soundhole. A cross-grain patch cannot serve this function, although it will alleviate the stress riser on the edges of the fingerboard that causes the top to crack there. The angled sides of the patch are carefully derived....the same width as the neck block at the upper end, and the same width as the soundhole at the bottom. That spreads the stress without localizing it. I also bevel the edges of the patch to further prevent stress risers.
I developed the design after repairing many, many vintage guitars that had the cracks on either side of the fretboard. In the worst cases, it is coupled with the shifted neck block that causes the fingerboard to push into the soundhole, resulting in a severe upturned neck angle. Though the pre-1939 14-fret Martins with no popsicle have a higher incidence of the failure, I have seen and repaired many guitars with a popsicle as well. So far, I have had 100% success using this repair method, sometimes replacing huge oversize 'popsicle' braces that had been installed by previous 'repairmen'.
Author:  Joe Sustaire [ Tue Mar 01, 2011 8:36 am ]
Post subject:  Re: How many builders use an A-Frame rather than a Popsicle brac
Hey John, I like your thinking and explanation of your trapezoidal patch, I'm going to incorporate that into my builds.

Also wanted to give a general thank you for your postings here and on other forums. It sure is a huge help to get some feedback from someone that has seen and repaired the problems guitars can give us.

Thanks again!

Joe
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/