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Rond - Posted - 08/21/2008: 13:54:38
Hello,
If you remove the resonator and notice that the corners of the ouside feet of the bridge are causing a slight but noticeable indentation is the head at this point torqued too tightly?
Should the feet profile under the head remain flat?
Ronald
1four5 - Posted - 08/21/2008: 14:13:24
This is a great subject, because in my limited experience this is normal. It's also what I noticed, and I couldn't help but think of how uneven the pressure is in the feet, and weather or not this may be effecting the balance and effectivness of the bridge. I also couldn't help but notice the sagging condition of the bridges on some of the old junker banjos I got from Goodwill... caused by the very natural dishing of any banjo head.
So I began experementing with 'dishing" the bottom of my bridges, and when the imprint in the bottom of the head is even, I know i've got it just about right. It might be my imagination, but might not...but I think they sound much more balanced, and even so, I can at least rest knowing that my bridge will never sag.
Dean
Edited by - 1four5 on 08/21/2008 14:16:13
Tyri - Posted - 08/21/2008: 17:23:10
Howdy, Ronald. Welcome!
I've been "dishing" my 4.25" w-i-d-e bridges the same as brother Dean, though Bart Veerman got me started. When I set one of these bridges on a table, the outer legs are hanging about 3/32" to 1/8" from the surface.
In my case, this is neccessary, but I've found that dishing increases the volume and "clarity" of every "standard" bridge I've tried it on, as well.
Dean: I don't think you're imagining it, but then, I've been informed by reliable sources that my grasp of reality is often tenuous. 
Happy experiments!
-Brywn
Gran Tyhri''s favorite Scot
Rond - Posted - 08/21/2008: 18:16:33
Yes,
That's what I thought.
If the outside feet are protruding in order to get a good head tension it must certainly kill some of the vibration.
Accordingly; if you lessen the head tension so that a normal undished bridge remains even the head is probably not tight enough to conduce proper vibration.
Why is this not address in set up books,
Have many of you experimented with this
Ronald
Rond - Posted - 08/21/2008: 18:18:35
Oh,
Many thanks for the welcome.
Cheers,
Ronald
1four5 - Posted - 08/21/2008: 19:34:15
quote:
Why is this not address in set up books
It's made enough of a difference, that I wonder the same thing. Especially in something important like sag prevention. I can only guess that it would be too much of a tooling hassle and added expense for high volume manufactures to mess with it. And without mechanical aptitude and some minor crafting/modeling or woodworking experience, the chances for botching up good bridges and messing up set up is probably very high. That's probably why it's not more common.
quote:
... I've found that dishing increases the volume and "clarity" of every "standard" bridge I've tried it on, as well.
Thanks!!! That makes two of us! I'd love to hear from someone who's tried it, and hasen't noticed a difference. Or better yet, just get some more pickers to try it, and report their findings. I didn't think I was imagining things...
And... one of the things that I've noticed on 100% of my banjos all the way from my beginner banjo, to the junkers I've fixed up, to my Deering Calico to the many many banjos i've played in music stores... the bridges sag. It's natural. If they didn't they would be defying the laws of physics. It took me about a year to figure out why I could finger pick my guitar like a maniac, but struggle and wiffed on my banjo. Once I pinned it down to my hand mechanics and the radiused guitar saddle vs flat to sagging banjo bridges... it all made sense. Now I dish the bottom of my banjo bridges and even slightly radius the top, and now my banjos play like butter. I can only bet there are pickers (especially guitar players) that are struggling, who would be blown away with this slight improvment.
Dean
Edited by - 1four5 on 08/21/2008 19:47:39
Bart Veerman - Posted - 08/22/2008: 06:50:59
The strings at about 6~8 lbs a piece + whatever tension the tail piece adds, exert a wicked number of PSI's on the bridge. The head being flexible, it simply does its job and flexes.
Most bridges have a flat footed profile and that works well. Like others have mentioned, "dishing" works even "weller." I hope you don't mind Dean, I've ripped off your image and added to it to illustrate my twisted thinking:
The taller middle leg, at the X, now can act as a fulcrum so the bridge can move/vibrate up/down more freely in the directions shown. I borrowed this idea from violin bridge designs and found it to work quite nicely on banjos so I made it a standard feature for the three legged bridges I make from the get go. It lets me squeeze a bit more horse power & tone out of a banjo and of course, it'll minimize and/or prevent sagging.
Bart Veerman, Bridge Maker
"an only banjo is a lonely banjo..."
free tabs: http://haruteq.com
1four5 - Posted - 08/22/2008: 07:16:28
Thanks Bart! I love the addition to the picture and the explination!
Dean
Clay (Slim) - Posted - 08/22/2008: 10:06:12
Interesting topic! I'm a new forum member and novice player -- just picked up my first banjo on Monday. I noticed the phenomenon described here on the underside of my head and, having some background in engineering, would like to do a little analysis of the string / bridge / head interaction. Can anyone (luthier preferred) give me some ranges for the angles of the strings in both directions from the bridge (alpha to the nut, beta to the tailpiece)? Also, Bart mentioned 6-8 lb of tension per string. Is that right? Seems like I heard that guitars have more like 30 lb per string (180 lb total). Is there really that much difference? Finally, is it generally accepted that the most preferable setup is to have the strings all in a single plane, or does a little positive radius improve playability? With this, we'll make the perfect bridge!
1four5 - Posted - 08/22/2008: 11:13:31
Welcome to the forum Slim!!! I hope you're ready for a lifetime study! I can't answer your scientific questions (I'm also more of a junkyard wars type guy than a luthier...) but I can tell you that for me personally, a slight positive radius makes a WORLD of difference. However, that's just me. I think you'll find that this will be different with every picker! I'm looking forward to your experiments and results, and you may also be interested in what BHO member xnavyguy has done recently in bridge technology... between you guys, you might build a banjo with a consciousness that reproduces
Dean
Edited by - 1four5 on 08/22/2008 11:16:27
Clay (Slim) - Posted - 08/23/2008: 18:00:55
Since my last post I have spent some time on Bart Veerman's website on the different factors that go into selecting the right bridge. Wow. I think I'll leave this one alone. And what a cool little niche he's found in the banjo world. Years of trial and error are better than cold analysis. I do, however, want to know what to do with my bridge. I think it's the one that came with my Goodtime. Should I go in and taper 3/32 - 1/8" off the ends of the feet? It really looks like there's a lot of stress on the head at the ends. Maybe I should just leave it alone until I'm ready for a new head, then order one of Bart's bridges. It sounds fine, although the fourth string does sound a little dead, and I would like to get more radius on my strings.
