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#1
02-24-2017, 10:41 PM
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Radius the bridge plate caul??
I've posted a few times about a Bourgeois I'm repairing (going well thus far, will update as things progress). I'm planning to put a radius in the bridge plate caul but wanted to pick your brains to see if there's any danger I'm unaware of.
When I flattened the belly, using Thompson aluminum cauls, I managed to flatten the bridge plate and top around the bridge successfully. But, it's ruler-flat. I would like to restore some of the original dome to that area. The new bridge form Bourgeois is slightly concave to match a new Bourgeois top. I was going to put some sandpaper under it, facing down, and put a slight dome in the bridge plate caul. I happen to have some 1" zebrano lying around that is hard and seems like it would be a good candidate for the bottom caul. The plan is to heat the bridge plate like I did when reducing the belly, and then apply the bottom caul along with the bridge acting as a top caul (dry, no glue) to get some dome back in the soundboard around the bridge. After it cools and looks satisfactory, sand the bridge to fit the top shape perfectly, and glue the bridge as normal. So, is there any negative in making a convex bridge plate caul (that matches the radius of the bridge and original radius of the top) in this situation? This might be a bit "outside the box" and convoluted but thanks for taking the time to read and understand what I'm talking about here. 
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#2
02-25-2017, 09:29 AM
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I see no benefit by inducing any radius in that area. String tension tends to do that as it is, and since the guitar has already suffered there, I'd probably flatten the bottom of the replacement bridge - it could only help resist the string tension.
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Cheers, Frank Ford
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#3
02-25-2017, 10:37 AM
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I see a lot of makers/repairers talking about radiusing their bridges, but I have never done that. I do use a flatter top a than some, but radiusing a bridge has never made sense to me. As Frank suggests, it will happen on its own, and IMO encouraging it is counterproductive.
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#4
02-25-2017, 11:30 AM
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Quote:
If we were to radius it the other way - in the opposite direction of the pull of the strings - that might be useful. Given the number of successful guitars in the world, it seems curving it that way is unnecessary.
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#6
02-25-2017, 01:23 PM
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Intuitively, I would have assumed that radiusing the underside of the bridge to fit the curve of the top was a good thing, but the unanimous opinion of four such luminaries persuades me otherwise. Just shows that intuition can lead you astray. I believe John Arnold also glues his bridges flat.
If the domed radius of the top is 25' , and your bridge is 6" in length, then the distance between the top and the ends of the bridge when laid flat is only .015" at either end.
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#7
02-25-2017, 02:50 PM
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Quote:
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#8
02-25-2017, 03:58 PM
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Thank you all for the responses. I really appreciate it.
My mind goes back to the fact that Bourgeois built this with a radiused top and, as MurrMac said, it seems intuitive to restore it to the original form. The belly and warping may have been due to a humidity issue (there's signs of a humidifier spill). I think I'm caught up on the idea that getting as close to factory as possible is ideal for the tone but, if you don't think it will make much of a difference then I'm going to trust the collective wisdom here. If it's a matter of extra work, I don't mind that at all since this is a personal instrument and means a lot to me. But, if additional heating and forming is going to do more had than good, then I will leave well enough alone.
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#9
02-25-2017, 07:29 PM
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When I build a top, I will make the braces and force the top and braces to conform to a shape example a 40ft arc by pressing them together.
When I fit my bridge plate on, I'm also using my 40ft caul and go bar deck to join the two pieces together, so in essence I am shaping the bridge plate to an arc. Would there be benefits from pre radiusing an arc into a 3mm thick bridge plate, I personally don't think so, when I force a flat piece of wood into an arch it will inherently want to spring back, so this will actually add some more strength to the area in resisting string pull, albeit small and possibly impossible to quantify or measure. When the bridge goes on, the top deforms around the bridge, only the x brace locations won't deform, so bridge shape imo is the more important component. Steve
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Cole Clark Fat Lady Gretsch Electromatic Martin CEO7 Maton Messiah Taylor 814CE Last edited by mirwa; 02-25-2017 at 07:37 PM.
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#10
02-25-2017, 10:04 PM
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Quote:
 My reasoning really is because any of the books that I used when I first started building, they all had arched braced tops but no one ever mentioned fitting the bridge or bridge plate to it. And intuitively it just didn't seem necessary. And actually since that time I have developed my own style which is a true flat top, in the lower bout, that is canted from the waist forward to the head block whit an arched UTB. I don't feel the need to arch the underside of the fretboard tongue for the same reason...
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#11
02-26-2017, 05:56 PM
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Thanks again, everyone. Very insightful. After mulling it over a lot, I feel confident about just sanding the new bridge flat and not messing with the radius. The braces on this instrument are incredibly thin for such a large body, so I think there's a validity to applying it flat, even if it wasn't the original design.
I'll post a progress thread when this thing comes back together, because I've received a lot of good advice from members here.
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