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Classical guitar "wrapover" bridge....
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=42636		 Page 1 of 1
Author:  Nick Royle [ Tue Feb 04, 2014 4:57 pm ]
Post subject:  Classical guitar "wrapover" bridge....
I saw a photo of a classical "wrapover" bridge, and immediately latched onto it for my current build as it allowed me to have a curved bridge with nylon strings but now I'm a little scared that in bucking tradition I may be setting myself up for a fall.

Here's the plan...
(The drawing isn't totally up to date. The top view is closest to the actual measurements.)

Attachment:
BRIDGE-DESIGN.jpg


I'm worried that I'm increasing the chance of the bridge peeling off from the back. Am I visualising the forces incorrectly, or is this indeed going to create more leverage than a traditional bridge design?

Thanks in advance for any advice/suggestions!
Nick

PS Anyone think the saddle slot isn't deep enough? Any other issues?
Author:  Jim Kirby [ Tue Feb 04, 2014 6:29 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
It's not going to increase stress on the joint. Viewed as a free-body, the overall bridge is still pulled on the same way and attached to the top in the same manner, so I see no difference. Sufficient seating of the saddle is a better question. What in particular of the overall design requires a difference in the tie block and string path?

Amplifying on this in an edit: Introduce a cut out depression behind the saddle as you would on a regular bridge. Both the high area around the saddle and the high area of the tie block can blend smoothly into the bridge wings. Lot's of bridges built that way.
Author:  Nick Royle [ Tue Feb 04, 2014 8:16 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Thanks Jim! That rests on my mind on that count but you're right, I was worried about the depth of the saddle slot with the strings passing underneath...

At first, I went for the wrapover design because it gave me total freedom with the shape and I was considering an asymmetric bridge. When I reverted to a symmetrical bridge, I kept it so I could curve the back edge.

The only thing that really makes me want to do the traditional bridge now is the saddle slot depth. If the consensus is that it isn't adequate, then I'll have to change my plans.
Author:  Steven Odut [ Tue Feb 04, 2014 9:02 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
What about the weight of the bridge in comparison to the traditional design? Your design looks to be heavier, which may have some dampening effect.
Author:  Nick Royle [ Tue Feb 04, 2014 9:17 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Cheers for the feedback Steven! I had a feeling it would be ever so slightly lighter actually but only because it's a flat 2mm everywhere but the central block (the lower drawing's saddle is misplace/wrong size, so the amount of wood either side of it is more accurate in the top view)... But I could be wildly wrong. And I figured it would be nice and stiff in the middle but more flexible at the wings.

Can a tie block bridge have a curvy rear end? I'm kinda attached to the bridge shape now.
Author:  Jim Kirby [ Wed Feb 05, 2014 6:27 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Nick Royle wrote:

Can a tie block bridge have a curvy rear end? I'm kinda attached to the bridge shape now.


Sure, why not? I would still put the regular valley in between the saddle and tie block and have the first string pass be through rather than over the block, to get the right break angle over the saddle.
Author:  Clay S. [ Wed Feb 05, 2014 8:40 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
I did a "wrap over" bridge for a ukulele, although I didn't know that is what it was called at the time. It worked fine.
Are you building an instrument with 10 strings? ( I noticed 10 holes in the bridge drawing)
Author:  Nick Royle [ Wed Feb 05, 2014 10:09 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
I'm going to have to think it over, Jim, thanks for the input! I'll do some drawings and work out string break angles, etc.

Glad to hear it worked for you Clay! This guitar is for a child so it has a narrow short neck to fit her hands. After all this work, I didn't want it to only be a usable guitar for 2 or 3 years, so the bridge is pre-drilled for 6 strings and for 4... When her fingers get too big for the 6 string spacing, this guitar will spend the rest of its life as a baritone uke! This is the build thread: http://www.luthiersforum.com/forum/viewtopic.php?f=10130&t=42550
Author:  Clay S. [ Wed Feb 05, 2014 7:01 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
"the bridge is pre-drilled for 6 strings and for 4... When her fingers get too big for the 6 string spacing, this guitar will spend the rest of its life as a baritone uke!"

Neat! I think you solved a design problem I have been wrestling with. Thanks!
Author:  Nick Royle [ Thu Feb 06, 2014 5:22 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Great to hear it, Clay! I copied James Ringlespaugh (sp) I think. If I remember correctly, he made a uke that could be strung up with 4 or 5 strings.
Author:  Nick Royle [ Wed Feb 12, 2014 10:53 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
This is it with a tie block rather than the wrapover style... How does it look?

Attachment:
BRIDGE-DESIGN.jpg


Does the tie block need bone or shell wear strips cos I don't know how i'd install them?
Author:  Jim Kirby [ Wed Feb 12, 2014 2:17 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Nick Royle wrote:
This is it with a tie block rather than the wrapover style... How does it look?

Attachment:
BRIDGE-DESIGN.jpg


Does the tie block need bone or shell wear strips cos I don't know how i'd install them?


Looks good to me.

You probably should have bone wear strips on the top edges of the tie block, or you will gradually get wear on the wood. For a regular classical bridge, for those of us who do the basic cuts on a table saw, a ledge is cut for these during the basic shaping of the tie block. I'm not sure what your sequence of operations will be so it's hard to say.
Author:  Nick Royle [ Wed Feb 12, 2014 3:45 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Thanks Jim! Very kind!

I just realised that I'm going to be better off not actually tying the strings off, even with this new improved design... The main benefit as far as I can see, is being able to remove the strings easily during setup (correct me if/when I'm wrong)... Well, I'm going to be better off removing the strings from the other end because I'm using PEGHEDS with a 7mm string post which will mean very limited space for string winds, so I need to pull the strings pretty tight before tuning up and starting the wraps.

So... I'll do the tie block bridge and get the proper saddle seating and correct string break angle, but I'll still tie a knot in the end of the strings and have it operate like a pinless steel string bridge. That way I also won't need the wear strips.

I don't have a table saw or anything so I'll be doing the following, I think:

- Drilling the string holes in the "tie block" (I've made an aluminium guide to ensure accuracy)
- Routing saddle slot and tie block front edge (actually, may saw the latter)
- Chiseling ramp from tie block front edge to 1/16th from saddle slot
- Sawing to shape, cleaning up to the lines by holding over thickness sander
- Sanding wings with thickness sander
- Final shaping and refining.

Things may change slightly on the fly but that's roughly how I'll do it.
Author:  Clay S. [ Wed Feb 12, 2014 4:29 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
For my "travel guitars" where I want the strings to be easily removable, I do an undercut (with a cove bit) on the back of the bridge and slots and ramps for the strings to fit into. The undercut area partly hides the ball ends as well as allowing the strings to be secured to the bridge.
Author:  Jim Kirby [ Wed Feb 12, 2014 4:49 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Nick Royle wrote:
Thanks Jim! Very kind!

I just realised that I'm going to be better off not actually tying the strings off, even with this new improved design... The main benefit as far as I can see, is being able to remove the strings easily during setup (correct me if/when I'm wrong)... Well, I'm going to be better off removing the strings from the other end because I'm using PEGHEDS with a 7mm string post which will mean very limited space for string winds, so I need to pull the strings pretty tight before tuning up and starting the wraps.

So... I'll do the tie block bridge and get the proper saddle seating and correct string break angle, but I'll still tie a knot in the end of the strings and have it operate like a pinless steel string bridge. That way I also won't need the wear strips.

I don't have a table saw or anything so I'll be doing the following, I think:

- Drilling the string holes in the "tie block" (I've made an aluminium guide to ensure accuracy)
- Routing saddle slot and tie block front edge (actually, may saw the latter)
- Chiseling ramp from tie block front edge to 1/16th from saddle slot
- Sawing to shape, cleaning up to the lines by holding over thickness sander
- Sanding wings with thickness sander
- Final shaping and refining.

Things may change slightly on the fly but that's roughly how I'll do it.


I think I'd probably still put a plate on the back of the tie block since you are going ot have knots or string balls bearing against that, or there are also these things that are individual little plates that you thread the string through and then they bear against the tire block with a bigger footprint than just the string knot - I can't remember what they are called - too late in the work day :^P
Author:  Nick Royle [ Wed Feb 12, 2014 5:06 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Interesting, Clay, though I'm not sure if I'm visualising it correctly. Do you have a photo?

By the way, an update on the extra string holes....

Attachment:
BRIDGE-DESIGN.jpg


6 string uke now so no need for work on the headstock or even to remove tuners when it goes through "the change" :lol:
Loving the idea of the 6 string uke.... Will mess up my straight string pull headstock a bit but better than any alternative!

And Jim,
I've got a piece of bone suitable for inlaying in the back of the block, I'll give it a go! I'm not sure how I'll rout the cavity for it, I suppose I can surround it with a jig actually. So many things to think about!!!! I think I'd better call it a day, too! I'm easily confused :)

Thanks for all your help!
Author:  Nick Royle [ Wed Feb 12, 2014 5:54 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
This pic better shows the two string spacings....
Attachment:
BRIDGE-DESIGN.jpg


I don't think I'll be able to inlay bone for the rear... And there isn't much meat between some of the holes.. so maybe it'll wear poorly, but hopefully there wont be any catastrophic failures. eek

I also need to make sure there's enough space between the strings on the double courses!??? They won't be hitting each other will they?

Here it is with a bit more space for the double courses.

Attachment:
BRIDGE-DESIGN2.jpg


Not quite even but I don't think I can get it much better... Hmm... It has to be a 6 string rather than 4 string uke. Just makes so much sense in this case. Maybe I'll just have to accept a less than ideal string spacing on it.

EDIT:

Attachment:
BRIDGE-DESIGN5.jpg


Slight rearrangement... More meat around holes and now it can be strung as a 4 string uke, a 6 string uke, and a 6 string guitar! 3 in 1! :)
Author:  Clay S. [ Sun Feb 16, 2014 4:20 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Hi Nick,
I finally got some pictures of the bridge. The pearl dots cover small bolts that provide additional sticking power to the bridge. Although the br8idge will hold without them under normal tension the bolts keep it on when someone tunes everything a step or two higher (which seems to happen when they are out with the general public).
Author:  Nick Royle [ Sun Feb 16, 2014 4:51 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Thanks, Clay, that's a very elegant solution to the problem! After some thought, that is roughly what I imagined you meant.

Here's how mine is looking at the moment (still far from finished! Will be much neater and prettier when I've finished carving and sanding it! Don't judge me! eek :lol: [I didn't have the router bits I needed so I used a Dremel and totally won't be doing that again! Darn thing!])

Attachment:
bridge-wip.jpg


I could use my KMG Binding machine-style jig to cut the rebate quite nicely on the back of the bridge... No real reason why I shouldn't. Maybe they'll annoy me when it's finished but I'm not overly concerned about the knots being visible. I'll have to think about it!

Does it complicate the scoring/taping/scraping etc when playing and gluing the bridge? I'm going to be scraping French polish back to glue the bridge.
Author:  Clay S. [ Sun Feb 16, 2014 5:16 pm ]
Post subject:  Re: Classical guitar "wrapover" bridge....
When taping the bridge area before finishing I just place the bridge in position and mark around it with a pencil on the tape. I cut the tape with a razor blade and remove the excess as I would any other bridge taping job. I cut the saddle slot with a router after gluing the bridge to the soundboard.
No reason you couldn't tie your strings like a typical classical if you decide you don't like the knots, but hiding them in a rebate would work too.
Author:  Nick Royle [ Tue Feb 18, 2014 11:57 am ]
Post subject:  Re: Classical guitar "wrapover" bridge....
Gluing the bridge was one thing I listed as "must do better next time", so I think I'll forgo the rebate on this occasion.
Thanks Clay!
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