Guitar Back Ladder Braces

[Mdinterman]

I don’t understand the use of ladder braces on guitar backs as there are no stresses imparted to the back that are perpendicular to the center axis of the instrument from the peg head to the tail block. Ladder braces would restrict movement of the upper and lower back from “folding” forward around the center line of the guitar, if you know what I mean. Seems to me an X brace on the back would be appropriate given that the strings impart a stress that would want to pull the back forward and up towards the peg head. I understand the sides would act to restrict the back from “curling” forwards from the tail block to the peg head. But what are the ladder braces doing when there are no forces perpendicular to center axis. Why not brace to restrict the strings from pulling the tail block end of the back toward the top and to the peg head?

What am I missing here?

[redir]

Originally Posted by Mdinterman

What am I missing here?

History and tradition

Also and the fact that it is time tested and proven to work. But there are many makers now doing asterisk of x-braced backs so go for it.

I have been favoring ladder braced backs with the low wide lower bout bracing. I think it livens up the back real nice. So there is tonal considerations in a back too.

[arie]

i think way back in the day somebody saw a rowboat and figured they'd go with that.

myself, i like the control of a double x

[yellowesty]

There can be some serious "stresses imparted to the back that are perpendicular to the center axis of the instrument" when it gets bumped into something.

[John Arnold]

Seems to me an X brace on the back would be appropriate given that the strings impart a stress that would want to pull the back forward and up towards the peg head.

You are correct in that the back is under tension, but that does not mean that longitudinal braces would be an advantage. You cannot stretch wood along the grain. The only thing that will happen as a result of this tension is that the arching of the back may flatten. Ladder braces will resist this flattening better than X-braces for two reasons. They are shorter than X-braces (which makes them stiffer), and they reinforce the back in its weakest direction, which is perpendicular to the grain.
In other words, use X-braces to make the back more active (more flexible), not because they are superior structurally. They are not.
X-braces work on a flat top because the stress imparted by the strings includes torque applied by a fixed bridge. X-braces resist this torque, but still allow flexibility.

[printer2]

And that big hole in the top probably adds some also.

[Alan Carruth]

The actual static longitudinal load on the back is small. I make 'test mule' guitars using a removable neck (so I only need one) that is basically held in by string tension. It hinges at the fretboard, and is kept from tipping up by a bolt into a T-nut inside. There's a gap between the heel and the side, which I normally fill with a wedge. Without the wedge it's really easy to pull the neck back and fret the strings out on the body fret. You can push the heel in with finger pressure. The strings are not so far above the top, and the length of the heel gives plenty of leverage.

Over the decades I've used a lot of different back brace schemes, and seen a couple I have not tried myself. They do tend to sound 'different', but not necessarily 'better'. Over the past few years I've gone back to ladder bracing on the backs, using two tall and wide ones above the waist, and one or two (depending on the guitar size) low wide ones below. It works as well as any, and gives me some control over the tone. If it sounds a lot like what a certain American guitar manufacturer has done since about 1833, you're right.

"When the need is old, the old ways are probably the best (unless some new technique has been introduced), since it is inconceivable that all of the designers of the past ten or twenty generations will have been fools"

(David Pye)

[cobalt60]

Originally Posted by Mdinterman

I understand the sides would act to restrict the back from “curling” forwards from the tail block to the peg head. But what are the ladder braces doing when there are no forces perpendicular to center axis. Why not brace to restrict the strings from pulling the tail block end of the back toward the top and to the peg head?

What am I missing here?

Perhaps think of the sides and their linings as "very long and curved braces" that travel in the direction you're talking about. Not only do they actually serve the function you're describing, but in many guitars (domed or otherwise), the longitudinal grain is also slightly bent in that long-grain direction, making it QUITE rigid.


Part of the real answer here comes from the tradition of building styles. If you brace the back before attaching it (domed or cylidrical), you've bent the back with the braces first, then with the sides second. In the days before vacuum bags for brace glue-ups, this was MUCH easier than pressing, say, a domed lattice into a flat back.

[dekutree64]

Originally Posted by Alan Carruth

"When the need is old, the old ways are probably the best (unless some new technique has been introduced), since it is inconceivable that all of the designers of the past ten or twenty generations will have been fools"

(David Pye)

The steel string guitar is quite a young instrument, though. There's probably room for improvement, especially in resisting long-term deformation.

I don't like the X/asterisk type patterns because they leave large unsupported areas between braces, which feel squishy if you press on them. Ladder bracing minimizes the brace-to-brace distance along the grain, so everything is well supported.

Lattice is good, but a lot of work.

Regarding back radius, my feeling is that cylindrical is better than spherical. Longitudinal arching certainly improves strength perpendicular to the plate (impacts or pressure on the back), but provides some slack to be stretched straight as the headblock rotates. Starting out with a straight run from head to tail doesn't give the headblock anywhere to go.

Here's a thought for a radical redesign... orient the grain of the back so it runs from one side of the guitar to the other, and then use two long braces running from the headblock to an inch or so either side of the tail block. Essentially a ladder rotated 90 degrees Would give minimal distance between braces along the grain for good strength, and maximum stiffness in the head-to-tail direction to resist headblock rotation.

The only thing I'd worry about is that humidity expansion/contraction would be in the direction to cause headblock rotation. So might need to veneer the inside and outside to restrain it (with the convenient side effect of making it look normal). But then it's a plywood back, so I'd need some slick marketing to convince people that it has any advantages over a normal ladder braced back