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This weeks post on TLB is about bridge design

http://www.theluthierblog.com/articles/ ... ge-design/

Have a look through - using the lists and questions in the article, can you see what's going on with your design?

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nigel

http://www.theluthierblog.com

there are a few simple facts on bridges.

1 it needs to withstand the stress applied

2 The foot print of the bridge will influence how the strings load will be transferred onto the top.

3 This is more complex than just the bridge as the bridge is the only brace that is glued on the outside. The ( bridge ) structure of the entirety must be considered. The means the bridge plate , the braces and the bridge all work together.

One piece of advice I will pass along is that the break angle is not as important as you may think. Many builder make this assumption but in reality it is the height of the strings off the top that is more important. Also when figuring out the applied load you also have to consider the point of attachment of the strings.

From an engineering point the forces of the strings are coupled at the bridge . the ball end is pulling up the strings are also pushing down on the saddle , these cause a rotational force on the bridge.

Now you can use this to help control the top. More often than not new builders tend to over build the bridge .

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John, if you are saying that the rotational force on the bridge is affected by the distance between the top of the saddle and the anchor point of the strings, I would have to disagree. The only parameter which affects the rotational force is the distance between the top of the soundboard and the top of the saddle (or the underside of the string, which comes to the same thing). The location of the end of the string has no bearing on the issue. If the bridge plate were 2" thick, it would not exert one iota more torque on the soundboard than if it were 1/16" thick.

Edit...

Removed because I mis-understood a statement and the point I was going to make was irrelevant.

Some aesthetic factors to consider:

How does the bridge width relate to the lower bout width of the guitar? Small bridges can look awkward on large guitars, even if they're structurally sufficient.

Frown or smile? Taylor's bridge is a very obvious smile.

Symmetrical or not? This can be structural as well, especially on fan frets.

What sort of shape do the bridge pins make? With unslotted pins (which I hope everyone is using to avoid future bridge plate trouble), you can vary the slots in the bridge to get constant break angle across the strings regardless of the pin locations, so I consider this mostly an aesthetic choice. Though really deep slots do cut into your stiffness (pun )

Do you restrict yourself to a convex outline, or allow dips and points?

The bridge is one of my favorite places to fancy things up, because it's 3D, and thus a good place to do some wood carving. I've never managed to come up with a fully convex shape that I liked, though it probably would be better structurally.

Here's one of my favorite bridges I've done, on a fan fret harp guitar... aside from the fact that my attempt at a straight line of pins was a failure But I recently bought a 4mm brad point bit that should give better accuracy for the future.


And the bridge for one of my guitars in progress. This one was a challenge to get the weight down, being African blackwood. The wings are thin, and the thickness ramps down in pretty much a straight line from a little over 5/16" in front of the saddle to 3/32" or so at the back edge. 24 grams. I love the warm black of the blackwood together with turquoise, and shimmery orange koa

I just take a Larson, Stella or Holz pyramid and copy it in African blackwood...