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Sep 28, 2021 - 11:54:22 AM

YellowSkyBlueSun

Virgin Islands (U.S.)

416 posts since 5/11/2021

Another thread made me think of this idea. Figured I'd throw it out into the aether and see what bounces back.

Has anyone ever tried to make a pile bent banjo bridge? Basically what I'm envisioning is 5 round columns, notched at the top, one for each string. Each column goes from the string directly (and independently) to the banjo head.

I'm thinking something similar to the image below, but without the cap. Just the piers and the cross bracing. Thoughts?
 

Edited by - YellowSkyBlueSun on 09/28/2021 11:56:16

Sep 28, 2021 - 12:17:32 PM

YellowSkyBlueSun

Virgin Islands (U.S.)

416 posts since 5/11/2021

One advantage of this design would be that you could specify each column to match the needs of each string. The wood species, density, grain orientation, and diameter could all be set individually. You could vary the column heights to match radius fretboards, offer a raised 5th string, or provide compensation.

The main disadvantage with this design is probably stability and rigidity. But if you could build it with the proper bracing, it might just work.   

Edited by - YellowSkyBlueSun on 09/28/2021 12:18:58

Sep 28, 2021 - 12:24:18 PM
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1532 posts since 4/13/2009

There's little new under the sun. Roger Siminoff experimented with a variety of bridges back when he run Pickin' magazine. Here's a column from the Banjo Newsletter:  https://banjonews.com/2009-11/more_about_bridges.html

Sep 28, 2021 - 1:02:42 PM
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Players Union Member

RioStat

USA

5592 posts since 10/12/2009

I tried something similar years ago, except I used bone columns (that I turned on a little table top lathe) and ran them through a thin piece of maple just to get spacing and hold them upright.

Banjo sounded like a sitar......or worse.  I didn't know you could get "feedback and distortion" from an acoustic instrument !

Never tried it with wood columns.

Sep 28, 2021 - 1:40:47 PM

YellowSkyBlueSun

Virgin Islands (U.S.)

416 posts since 5/11/2021

deestexas Thank you for the link, excellent article. I sure do with the images were still available though, they don't show up on my browser. Looking at the description though it looks like Mr. Siminoff tried similar things but not the exact design I'm suggesting.

RioStat I think your right that having 5 individual points of contact introduces issues of wave interference. Might not be a good thing. But I wonder if the sitar sound was more from the material rather than the design.

Another question: If someone were to build this, would small dowels work? That would make the grain run vertical (normal to the head), whereas most bridges seem to have grain that is horizontal (parallel to the head). I imagine this would effect tone. The alternative would be basically coring a piece of wood and using the core cylinder as the column. But from what I've seen of wood core samples, they likely wouldn't stay together and the individual layers would separate apart. Off the cuff, I'd imagine the columns wouldn't be much more than 1/8" to 1/4" in diameter, at most. 

Edited by - YellowSkyBlueSun on 09/28/2021 13:42:42

Sep 28, 2021 - 1:41:22 PM

1612 posts since 2/9/2007

I'm guessing you'd be better off making it all of one piece, drilling and carving to approximate the shape, but you never know... As mentioned above, lots of experimenting has already been done with bridge design.

Sep 28, 2021 - 1:47:52 PM

YellowSkyBlueSun

Virgin Islands (U.S.)

416 posts since 5/11/2021

Dan Gellert I also thought of this, and it may be worth entertaining. What you describe would basically be an extremely slender "spillway dam" type bridge, with 5 legs instead of the typical 7 legs, and with the "spillway" holes elongated vertically and enlarged as much as possible. It doesn't quite provide the isolation that I had in mind because there's still a unified cap.

Edited by - YellowSkyBlueSun on 09/28/2021 13:48:23

Sep 28, 2021 - 1:51:12 PM
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13944 posts since 6/29/2005

I made this one years back, which I called the "stonehenge bridge".  It worked fine and was very light.

Sep 28, 2021 - 2:30:49 PM

8990 posts since 8/28/2013

One thing to worry about with strings passing over end grain of the bridge post is splitting of the post from down pressure. When people split logs, they almost always drive a wedge or an axe blade into end grain. I've never calculatyed the down force of banjo strings over a bridge, but I would think one would at least have to carefully align the grain to minimize this possible splitting.

I've alway though about making a "post" bridge using upright piano shanks, which are nothing more than maple dowels. I would, however, cut slots into the ends of those shanks to accept a crosspiece made of thin ebony, I'd also use at least one other brace lower down the posts to help hold it all together. If the end slots were made to fit the ebony, one might not need to glue this piece, although the lower brace would likely need some gluing.

I'm fixing one of my sister's guitars, helping my son repair his parch, and still need to tune and regulate my piano, but maybe when I'm through withn thse projects I'll consider experimenting with this bridge idea. Unfortunately, I also just remembered I've got to do something with my own back steps, rewire one room of my house, and add another electrical outlet in my "shop."

As tyhe saying goes, "I'm too old for this s**t."

Sep 28, 2021 - 3:07:23 PM

wtalley

USA

286 posts since 7/2/2010

Sep 28, 2021 - 5:45:14 PM

rmcdow

USA

1011 posts since 11/8/2014

It seems to me that if you put a slightly flared out foot on each one of the piers, you could have each string completely separate from the other strings, and just turn the piers on a lathe out of whatever wood you want to use. If it is a hardwood, I don't believe there is going to be a problem with splitting if you have the string running perpendicular to the growth rings, as the winter growth is going to be pretty hard. You would have the advantage of being able to adjust both the height of the posts and the spacing of the strings. If the posts did want to slide together, which would likely be the case with the wider spaced strings, you could make the flared foot wide enough where they would just touch each other. I don't know if it would work, but it does sound like something that would be interesting to try out, and not all that difficult.

Sep 28, 2021 - 6:12:15 PM
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13944 posts since 6/29/2005

Sep 28, 2021 - 9:17:28 PM

Bart Veerman

Canada

5043 posts since 1/5/2005

Yes, it would be doable to make a pile-bent style bridge like in the picture. Keeping in mind of course, with a banjo bridge there isn't a whole lot of real estate to work with so practically speaking, it would be a total PIA to even try. There's no reason for it not to work but, realistically, certainly not worth to effort to me. I'll probably get nightmares tonight dreaming about somebody sending me an order for 100 pieces of them...

Ken: your Stonehenge looks amazing! No doubt that it must have taken you quite a bit of time to make it.

George: measuring the string pressure of a string on the bridge comes up with t some far out numbers. Figure a "normal" 010 (0.254 mm) first string resting on a 2 mm long string slot:

  • 0.254 X 2 = 0.508 sq mm
  • 1 sq inch = 25.4 X 25.4 mm = 645.16 sq mm
  • 645.16 / 0.508 = 1,270
  • it takes approx 7 lbs force to lift the string off the bridge with an old fashion fish scale hook
  • 1,270 X 7 = 8,890 PSI

Yup, 8,890 lbs, and that's only when the full bottom half of the string makes perfect contact with the string slot. Seeing that as in the real world only a small portion of the string's bottom rests on the slot, well, the PSI number goes up well into the sci-fi range smiley

The small size of a banjo bridge doesn't leave much room for experimenting with styles, shapes etc. As fabulous as a bridge that looks like a garden fence might be, hmmm, it'll be a tough job getting folks to try one as Earl definitely never used anything like it... On the other hand, experimenting sure can be a whole lot of fun smiley

Sep 28, 2021 - 10:17:32 PM

rmcdow

USA

1011 posts since 11/8/2014

quote:
Originally posted by Bart Veerman

 

  • 1,270 X 7 = 8,890 PSI

Yup, 8,890 lbs, and that's only when the full bottom half of the string makes perfect contact with the string slot. Seeing that as in the real world only a small portion of the string's bottom rests on the slot, well, the PSI number goes up well into the sci-fi range smiley

The small size of a banjo bridge doesn't leave much room for experimenting with styles, shapes etc. As fabulous as a bridge that looks like a garden fence might be, hmmm, it'll be a tough job getting folks to try one as Earl definitely never used anything like it... On the other hand, experimenting sure can be a whole lot of fun smiley

 


From a rough on a napkin calculation, any wood with a Janka hardness above 1380 would hold up fine.  That's not considering the hardness of just the winter growth grain of the wood, but the average across both the winter an summer growth.  Hard rock maple just passes this, and I have had it hold up as a bridge material with no cap.  Any of the ebonys easily pass this, which is why ebony makes a good cap material.  Silver maple doesn't pass it, which is in line with my experience with it as a bridge with no cap.  Janka hardness doesn't specify whether the test is done on end grain or perpendicular to the grain, and is done with a .444" steel ball, so it can only be used as an indicator of hardness, which brought me to the back of the napkin. 

Crushing strength of the wood might be a better measurement to consider, as that pressure is applied parallel to the grain, but is not applied to a point location as with the Janka hardness.  Looking at Janka above 1380 and crushing strength above 8890 might be a way to consider if a wood would work alone, and if it didn't look good, put a cap on the pillar wood made out of a wood such as ebony or lignum vitae that would stand up to the pressure.  

Edited by - rmcdow on 09/28/2021 22:19:08

Sep 29, 2021 - 1:53:04 AM
Players Union Member

Helix

USA

14592 posts since 8/30/2006

I can see a separate post for each string that is not connected with a common top rail, but with a little top rail of its own.
then the "bridge" can be joined up with non vibrating sections.
Making each string independent from the others.
Then different woods could be used for each string.
And the bridge could be flexible to allow compensation to fit each person's ear and specs.
Ash for the 1st and 5th strings
Walnut for the 4th
Cherry the 3rd
Lilac for the 2nd just because we can.

I like the pier concept
I like vertical signal.

This bamboo is bookmatched with an Jatoba top and vertical middle. 


 

Edited by - Helix on 09/29/2021 01:55:51

Sep 29, 2021 - 4:42:15 AM

DSmoke

USA

1066 posts since 11/30/2015

I have 2 concerns with your design. You will have to make your center piles higher to compensate for the sag of the head. I imagine this sag will be slightly different than with a bridge that is connected. Secondly, and more importantly, I see this twisting, breaking, and falling over when bringing a string to pitch. You could test this with a single dowel to see how much it moves when tuning up a string.

Sep 29, 2021 - 6:35:25 AM

13944 posts since 6/29/2005

This would be a very easy thing to do a simple blind comparison of vs a standard design bridge.

Sep 29, 2021 - 7:01:15 AM
Players Union Member

Helix

USA

14592 posts since 8/30/2006

Uh oh a Smile Pile??

Sep 29, 2021 - 7:09:17 AM
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5726 posts since 12/20/2005

I built this years ago, don’t even recall what year it was.
I made a rough model to see how it would sound. Made it out of walnut with no cap.
Didn’t try to make it look good unless I would have really liked it.
I must not have been smitten by the sound because it is still rough and the only one I have.
I just now put it on my 1929 GB3. It is tuned toG,
g D G B D g. Has a calfskin head.

Actually it sounds pretty good.
I have not measured it but it is thin.
I will play it today and see how it goes.
It could easily fall over so I will have be watchful of that.


Sep 29, 2021 - 11:32:18 AM
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8990 posts since 8/28/2013

quote:
Originally posted by Ken LeVan


Aha! You are progressing architecturally. You've gone forward from "Stonehenge" to "Parthenon."  Maybe you should try a "Gateway Arch" in the future , although that would only work with a rather tightly radiused fretboard.

Sep 29, 2021 - 1:46:12 PM

89 posts since 3/24/2020

quote:
Originally posted by Leslie R

I built this years ago, don’t even recall what year it was.
I made a rough model to see how it would sound. Made it out of walnut with no cap.
Didn’t try to make it look good unless I would have really liked it.
I must not have been smitten by the sound because it is still rough and the only one I have.
I just now put it on my 1929 GB3. It is tuned toG,
g D G B D g. Has a calfskin head.

Actually it sounds pretty good.
I have not measured it but it is thin.
I will play it today and see how it goes.
It could easily fall over so I will have be watchful of that.


Maybe if it was flipped upside down to closer resemble the op's design & then report back on the difference 

Sep 29, 2021 - 1:49:53 PM

5726 posts since 12/20/2005

Structurally, I don’t think it would hold up, that way

Sep 29, 2021 - 1:56:27 PM

DRH

USA

652 posts since 5/29/2018

If you cap your individual posts in the manner most bridges are capped then the contact stresses will be the same as with a conventional bridge. So that isn't an issue.

The contact stresses for theoretically sharp breakover are Hertz contact stresses and don't follow Hooke's stress calculations. But the strings will seat themselves into the caps so the breakover isn't truly sharp. Your contact pressure can easily vary by a factor of ten in this transition region. So it still isn't an issue.

However, you have both downward and lateral forces, particularly at the outer strings. Then there are forces parallel to the strings that change every time you tune or play. If you don't tie the posts together those lateral and parallel forces will become bending forces on the posts. If they don't tip over you will find them dragging around the head every time you tune or play.

And once you tie the posts together you are back to a one piece bridge where each string interacts with the others. Frankly, I think that is what they are supposed to do.

OTOH, If someone told me it had already been done many times before, I would take that as a reason to try it again. The rest of us might have missed something.

When I got my first $60 banjo (1971) I was frustrated about the bridge wandering around. Larry (Helix) suggested I get a Grover Non-Tip like his. On such trivia long friendships are formed. BTW Larry, it's been 50 years this year. I'd come see you but after half a century of cumulative weirdness I'm afraid we would accidentally set off the LIGO detector up in Hanford.

Sep 29, 2021 - 3:21:49 PM

13944 posts since 6/29/2005

quote:
Originally posted by G Edward Porgie
quote:
Originally posted by Ken LeVan


Aha! You are progressing architecturally. You've gone forward from "Stonehenge" to "Parthenon."  Maybe you should try a "Gateway Arch" in the future , although that would only work with a rather tightly radiused fretboard.


I AM progressing architecturally, and my standard bridge design for the past ten years is based on a Roman arch—it would be hard to find a more simple and elegant way to transfer a load path to the ground, and I think it works equally well transferring the energy of the strings to a banjo head.

Edited by - Ken LeVan on 09/29/2021 15:23:03

Sep 29, 2021 - 4:46:55 PM

DRH

USA

652 posts since 5/29/2018

Ken;

I had many hours of frustration trying to intonate the six string with your bridge. Then I realized the angle of rotation was even more critical than position. Rotating allows me to hone in on the sweet spot. The effect is different than what one gets with a straight bridge. It's better.

Who knew an asthetic arc could do more than just stabilize the bridge? Well, I'm sure you knew, as do most of the people reading this thread. In my case it was a good mental exercise.

Sep 29, 2021 - 5:51:22 PM

8990 posts since 8/28/2013

quote:
Originally posted by Ken LeVan
quote:
Originally posted by G Edward Porgie
quote:
Originally posted by Ken LeVan


Aha! You are progressing architecturally. You've gone forward from "Stonehenge" to "Parthenon."  Maybe you should try a "Gateway Arch" in the future , although that would only work with a rather tightly radiused fretboard.


I AM progressing architecturally, and my standard bridge design for the past ten years is based on a Roman arch—it would be hard to find a more simple and elegant way to transfer a load path to the ground, and I think it works equally well transferring the energy of the strings to a banjo head.


I was, of course, joking about your earlier posts. 

I think I'll now get back to planning a new project, a geodesic banjo pot!

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