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Jan 19, 2025 - 9:03:55 PM
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2 posts since 1/19/2025

About a year ago I upgraded to a Gold Tone OB3 "Twanger". I have noticed that with light gauge strings the center G string is always sharp on a fretted note, even when in perfect tune as an open note. I started wondering if a compensated bridge would help. I started shopping around and didn't want to invest much money in an experimental fix, so I decided to try and make a 3D printed bridge as a first step before investing in a wood compensated bridge.

My fist attempt only compensated the center G string, and the results were a little disappointing. It had a bit of a buz and the tone was a noticeable degrade, but the intonation problem was better. So I went back to the drawing board and experimented with a few more prototypes. I think I have made 9 now, and I am pleased the latest model. In fact it sounds much better than I thought it would. It is still considerably heavier than a wood bridge. I hope to experiment with some carbon fiber reinforced materials in the future that may let me take more weight out of it.

If you have a 3D printer and you want to make one yourself, you can download the files at MakerWorld.com. Search for Compensated Banjo Bridge.

Jan 19, 2025 - 9:15:57 PM

28473 posts since 6/25/2005

A note because you mentioned carbon fiber. Some years ago I played a carbon-fiber bridge made by a banjo-playing Silicon Valley scientist. It was the worst-sounding bridge I ever tried. Your material may be different and superior, but I thought I’d pass my experience on.

@JimLarsen

Jan 20, 2025 - 2:52:27 AM

1805 posts since 1/9/2012

Sadly, my understanding of how bridges work is theory-based. My own hearing isn't worth squat and hasn't been for decades. But, based on what I do believe, I've got a couple of suggestions.

Overall weight is the biggest bridge issue. From your photo on MakerWorld, it looks like you could sand quite a bit off the back before impacting the compensation. (I'm assuming that the thickness is necessitated by the printing process.) Beyond that, the magic of individual bridges comes from how they flex. That, in turn, is a combination of the material stiffness and the bridge design. I imagine that your plastic is not as stiff as maple. Maybe a different shape to the structure under the black cap could stiffen it up. (The traditional design that you used evolved for maple as the material of choice.)

Jan 20, 2025 - 6:50:29 AM

Corwyn

USA

1715 posts since 1/9/2006
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The simplest take away is that you have found that a compensated bridge would help you problem.

I suspect that more tweaking of the design could reduce the weight, but I don't know if you would be up for making another 40 prototypes.

Thanks for doing the experiment, and posting about it here. Some traditionalists might object, but this is new knowledge and we all gain from it (even if that knowledge is just 'maple is still better').

Thank you kindly.

ETA: Are you printing in the slots for the strings?  If so, it might help to print that area as solid material and file the slots.  This allows exactly the right width (you may need a set of slot files (very cheap)).

Edited by - Corwyn on 01/20/2025 06:57:21

Jan 20, 2025 - 8:34:05 AM

16101 posts since 6/2/2008
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Jan 20, 2025 - 9:29:30 AM
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Bart Veerman

Canada

5896 posts since 1/5/2005

Since you can dial in the specs for a bridge you might as well do some measurements to figure out by how much compensation each string actually needs. This way you don't have to rely on the "about this much" method:

https://banjobridge.com/br-06.htm

Jan 20, 2025 - 9:58:18 AM

1980 posts since 11/10/2022

I do 3d printing often. Im not sure the capabilities of your printer but keep in mind materials matter. I use about 15 different resins and 7 epoxies which can print everything from metal chain to soft rubber treads. Im not even sure why bridges are wood and not metallic, but one could easily experiment with a 3d printer. The middle g 12th ftred not ringing well is common. My solution was a neck reset and slight uptune from g. I tried some compensated bridges but they didnt do well. A tight 93 head helped a lot also.

Jan 20, 2025 - 5:39:52 PM

2 posts since 1/19/2025

Well, like I said before, this is just an experiment that turned out better than expected.  I kept it kind of thick because I assume that wood is stronger than plastic. I didn't want to make it so light that it would easily break.  But I agree there are places where it could be made lighter.  As far as the materials, I am not even sure carbon fiber would be lighter because the carbon is just an additive to one of many possible types of plastic. I did order a compensated bridge from Banjo Ben.  I think that this banjo would do better with medium or heavy strings.  They are less likely to deflect when fretted and go sharp. Not only does my G string go sharp, but my capo makes everything go sharp.  I spend a lot of time tuning at jams and performances.  I now know that the bridge will help the G string issue.  Now I need to experiment with string gauges to see if I can reduce the tuning when using a capo.

Jan 20, 2025 - 8:27:07 PM

13302 posts since 10/27/2006

quote:
Originally posted by Bart Veerman

Since you can dial in the specs for a bridge you might as well do some measurements to figure out by how much compensation each string actually needs. This way you don't have to rely on the "about this much" method:

https://banjobridge.com/br-06.htm


What Bart says. The bridge is plenty thick enough that you can dial in each string with a file. Once the individual compensations are perfect, you will have precise measurements for the next round.

I know that printing maple is not possible but there may be a plastic more ideal. You should also be thinning one of your prototypes to see if less mass is possible without sacrificing stability.

My 2¢

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