Wednesday, April 27, 2011

Bridge Design

I’ve been making the bridge for Geoff’s guitar so I thought that take this opportunity to mention an often overlooked element; bridge design. Now you may ask, if I’m so interested in bridge design, why mine looks fairly “traditional” and not shaped like an asymmetrical dog bone with a spilt saddle?

Firstly, the function of bridge is to transfer as much of strings’ kinetic energy into driving the soundboard as possible. Therefore you want to have a light bridge so that the strings’ energy isn’t taken up overcoming the inertia of the bridge (remember Alan’s mandolin bridge). That said, any design solution is always the best compromise; the solution that best fits all the conflicting specification points. Read on......

So, although I want a light bridge there are other considerations. You’ll notice, like some other luthiers, that I’m using a fairly wide saddle. The reason for this is to have more room for the adjustment of the strings’ intonation (there’s a good article on intonation on the Luthiers Mercantile International website). Some luthiers go for a split saddle but this just seems wrong to me; I feel that all the strings should be on the same saddle so that their vibrations can interact with each other, giving rich overtones. Also if the player ever wants to retro fit a transducer under the saddle, their options for a pick-up aren’t limited. The saddle slot is also cut deep for number of reasons; mainly so that the saddle is held firmly and doesn’t tend to lean forward (this would sharpen all the notes). Again, thinking of the future it’s deep enough to fit a transducer without having to route the slot any more, also if the action needs to be raised there is plenty of depth to fit shims under the saddle. With all the forces acting on the strings, there has to be a fair amount of wood in front of the saddle to support it.

Unlike many guitars, my bridge pin holes are parallel to the saddle; this gives a similar break-angle to each string- this break angle does affect the “feel” of the guitar and therefore should be close to equal on all strings. Also the pins are not evenly spaced. I use proportional spacing- the distance, centre to centre, between the 6th and 5th strings is slightly greater compared to 5th and 4th and so on. With evenly spaced pins, the gap between the 6th and 5th string is less than the gap between the 1st and 2nd, due to their comparative diameters. The use of pins to hold the strings makes a hardwearing wood such as ebony a suitable material- you could use lighter woods but I would be concerned that after a number of string changes the pin holes would wear.

I also like to cut 45 degree ramps for the strings so that they can break cleanly at a good angle over the saddle which helps to eliminate the risk of any odd buzzes.

The wings of the bridge are thinned to reduce some mass and all edges are rounded off so that there are no sharp edges for those players who like to rest the hands on the bridge. The curved belly at the rear of the bridge increase the surface area for gluing in a place where bridge can eventually pull up.

Quite a lot there eh? So that’s why you buy a hand made guitar!

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4 Comments:

Blogger Tico Vogt said...

I've been a guitarist for over forty years but know little about the design considerations from the luthier's standpoint. Your posts on this subject are well written and making me take a new look at my instrument.

12:35 PM  
Blogger Peter Brown said...

Gary, I never thought about proportional bridge pin spacing until now - food for thought!

While I'm here, where do you sit on the slotted/unslotted bridge pin argument?

12:46 PM  
Blogger Aprendiz said...

Hi Gary. Very informative this article, as the previus. I didn't know how much detalis are related to bridge design.

I'm and admirer of your work and hope to achieve the same level of excelence in the future. I'm beginning to build my first electric guitar as self learning luthier. Of course, blogs as yours are a great source of knowledge. I also enjoy watching your videos on youtube.
I had no previus experience with woodworking and It's been a challenge.

Congratulations!

3:07 PM  
Blogger Gary Nava, Luthier said...

Hi Pete,
After much chopping and changing, I’ve finally settled for slotted pins. If you have good clean ramps and decent pins you don’t have to cut into the soundboard and bridge plate as you do with un-slotted pins. Also I think that strings can be harder to remove if they get caught in slots cut into the guitar.

Hi Aprendiz,
Good luck with your building!
Cheers Gary

5:05 PM  

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