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| Articulated Bridge Clamping Caul http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=9732 |
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| Author: | jhowell [ Sat Dec 09, 2006 5:36 am ] |
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Not nuts at all! I prototyped (built a sloppy looking version with hand tools  ) that bolts through the bridge and top. Its an amalgamation of some stuff that I've seen on the web. I used it to clamp a pyramid bridge on my 0-16 replica last weekend. It makes the cleanup of glue squeeze-out a cinch as you have access all the way around the bridge.
I'll post some pics tommorow as it appears the social director has me booked for the day! 
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| Author: | Wade Sylvester [ Sat Dec 09, 2006 6:21 am ] |
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Ya Hesh, I think that is a good idea! I have tryed to keep my bridge patch flat, or at least where the caul touches it. but I make an extension to the caul with little wing pieces to extend the clamping beyond the x brace. I epoxie the wings to the caul so they are flat against that part of the top, conforming to the arch from the inside. But cutting a slot in the caul may be good especially if you are not sure your bridge patch is dead flat. Thanks, Jim, I'd still love to see that clamping system! Wade |
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| Author: | crazymanmichael [ Sat Dec 09, 2006 7:36 am ] |
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perhaps a better solution would be to use friendly plastic or floatation foam to mold a radiused caul. would work even better and is still very simple to do. |
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| Author: | burbank [ Sat Dec 09, 2006 7:38 am ] |
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Hesh, Is this what you're after? link The sixth photo in the sequence, "Sanding Bridge Caul Complete" gives me a caul that is contoured to my 30 ft. radius dish. I'll go this one better and make a caul that will support the wings of the bridge. |
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| Author: | Rod True [ Sat Dec 09, 2006 8:11 am ] |
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Laying this out on Cad gives me 0.015" for 25' radius and 0.0125" for 30'. Not much material to remove from the caul on the sanding dish. You could just sand it in your dish and call it a caul  just like Pat did.
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| Author: | Wade Sylvester [ Sat Dec 09, 2006 8:27 am ] |
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I have radiused the patch before gluing to the top. Is this a bad idea? Wade |
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| Author: | Dean [ Sat Dec 09, 2006 8:30 am ] |
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Hesh, just take a flat caul and put some friendly plastic on top and some waxed paper on that so you dont stick to the tone wood and clamp this in place and you have a perfectly mated caul. Rewarm for the next guitar. Dean |
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| Author: | JJ Donohue [ Sat Dec 09, 2006 8:42 am ] |
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I do the same thing that Pat showed. We always seem to find lots of good things to do with our 25'R "bus steering wheels". |
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| Author: | KiwiCraig [ Sat Dec 09, 2006 8:44 am ] |
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G'day Hesh, I radius the glue side of the bridgepatch on my dish ,by double taping it to a piece of one inch ply cut to the patch shape . That piece of 1" ply becomes the caul for glueing the patch to the soundboard , and later becomes the patch caul when glueing down the bridge. Radiusing the patch only removes a fraction of a m.m from it's edges. This way you don't have to concern yourself with a radiused caul ,OR forcefully bending the patch to conform to your soundboard radius. Another benefit is that the top's radius geometry is maintained , where as a force bent patch interferes with the true radius. It makes the job of radiusing the bridge bottom easier too . Everything fits "Snug " Regards , Craig |
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| Author: | Peter J [ Sat Dec 09, 2006 8:57 am ] |
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Hesh, I got this idea from an article I read a while back by Frank Ford to use high density packing foam as a caul. Here are two photos of the bridge caul that I use for my classical guitars. The foam is high density and can be compressed about 1/4" but it still provides a distributed clamping surface and conforms to the inner surface of the top of the guitar. I use a 25 ft. radius on my tops. The lower surface of the caul is just a piece of 1/4" plywood that the clamp jaws engage. It works great and I've not had any problems. The foam can be carved or cut to match any bracing pattern or form and is really an ideal, versatile material for cauls in delicate areas. 
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| Author: | Colin S [ Sat Dec 09, 2006 9:34 am ] |
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[QUOTE=Wade S.] I have radiused the patch before gluing to the top. Is this a bad idea? Wade[/QUOTE] Wade, I always radius the bridge patch, it's just another brace after all, as far as the top is concerned. If you radius the bridge and not the patch then they are fighting each other. Yes just radius the caul in the sanding dish. Colin |
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| Author: | KiwiCraig [ Sat Dec 09, 2006 9:49 am ] |
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Colin, Not sure I follow you here . If you radius the bridge patch , and glue it down with the top in the dish , you want a flat caul |
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| Author: | David Collins [ Sat Dec 09, 2006 10:15 am ] |
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I've always used thick stiff leather on most of my internal calls. This provides good stiff support but still has enough give to conform to minor differences. I always try to keep a good variety of leather scraps on hand of a variety of thickness and stiffness so I can choose appropriate padding for the whatever caul I'm using. If I feel I need some extra give I also keep some rubberized cork (gasket material) that I can layer under the leather. You could also kerf your bridge plate cauls - leaving a 3/16"ish backing should provide plenty of flex. |
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| Author: | Michael Dale Payne [ Sat Dec 09, 2006 11:56 am ] |
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I use friendly plastic. Heat it up. set it on a 1/4" thick play wood plank 2" wide x 6" long. laying it on about 3/4" thick. wait till it cools just a little so it wont stick to the spruce where it touches. position it and press. Somewhat like Peter with the foam. I do this while the top is loose as in not attached to the body. After it has set hard it is a perfect caul easy to position through the soundhole |
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| Author: | Tom Morici [ Sat Dec 09, 2006 12:43 pm ] |
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Hesh Here is what I use, Made them on the tablesaw. Cut the gridwork while the piece is square. Then cut the caul shape. Hope this helps. 
Tom |
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| Author: | peterm [ Sat Dec 09, 2006 1:03 pm ] |
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[QUOTE=Peter J] Hesh, I got this idea from an article I read a while back by Frank Ford to use high density packing foam as a caul. Here are two photos of the bridge caul that I use for my classical guitars. The foam is high density and can be compressed about 1/4" but it still provides a distributed clamping surface and conforms to the inner surface of the top of the guitar. I use a 25 ft. radius on my tops. The lower surface of the caul is just a piece of 1/4" plywood that the clamp jaws engage. It works great and I've not had any problems. The foam can be carved or cut to match any bracing pattern or form and is really an ideal, versatile material for cauls in delicate areas.
[/QUOTE] Great idea Pete!! Thanks |
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| Author: | JJ Donohue [ Sun Dec 10, 2006 1:12 am ] |
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Another issue about bridge cauls for me is worth mentioning...they're one time use only. I like to have a tight wood surface bearing against the bridge plate for drilling the 3/16" holes after the glue has set. It's important that the exit point of the drill produces a perfect hole with no chipout. Having fresh wood in intimate contact with the plate is the only way I know to produce this. Once I remove the caul, I toss it. |
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| Author: | Andy Zimmerman [ Sun Dec 10, 2006 1:43 pm ] |
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I use John Halls bridge clamp It works great. It isn't radiused, but I have had no problems with it. |
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| Author: | Rod True [ Sun Dec 10, 2006 2:39 pm ] |
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[QUOTE=azimmer1] I use John Halls bridge clamp It works great. It isn't radiused, but I have had no problems with it.[/QUOTE] What's this? Any pictures? Didn't know John made a bridge clamp????????  ?????
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| Author: | Michael McBroom [ Mon Dec 11, 2006 7:20 am ] |
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[QUOTE=Hesh1956] What I discovered is that when I radius the bottom of a bridge on the 25' radius form that I made in the 25'dish the bridge still will not sit "perfectly" on the guitar top. This means that even though we brace our tops and even radius our bridge plates in the dish the top is not always going to be a 25" radius - exactly. Probably RH plays a part in this too raising or lowering the dome. [/QUOTE] This isn't all that unusual -- at least on classicals. I find that sometimes a top will have "relaxed" a bit, but by insuring that my bridge's underside has the proper arch, when gluing the bridge in place, it will draw the top up into the proper arch. As several others have mentioned, I also use a bridge gluing caul that I've radiused in my sanding dish. By having the caul and the bridge pressing against the top from both sides, it should push the top into the required arch. Only problem I can see to this might be if there was some RH variances that occured while the top was being fitted to the sides, which might result in some internal stress to the top itself. I have a question about the bridge plate, though. You guys who build steel strings shape your bridge plates from hardwood -- and I'm assuming that it's well quartered to boot. So, if the plate has been contoured in a sanding dish, shouldn't it still be flat on the reverse side? If so, then it seems to me that you wouldn't need a contoured caul as well. If the reverse side has taken on the contour as well, it seems to me that the plate might have been distorted while sanding it, and chances are it might not be holding the proper arch at rest? Best, Michael |
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