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Posted

So, i got my soundboard all braced and its looking really good. The last thing i have left to glue is the bridge plate. I did the rest of it with the go-bar press i made and it worked flawlessly.. however the book i am using which is the kinkaid book, he does everything with the gobar.. and then does the bridgeplate with a g-clamp. He dosnt explain why (alot of that going on in that book), he just switches over. Is there any reason for this? Or do you guys use the gobar to glue it. Should i still glue it using my radius dish? or on a flat workboard? help!!

Rob

Posted

Use the radius dish. I guess he thinks you might not get enough clamping pressure over that wide area with the gobars, but I've never really had a problem with it mating well, I use 4 or 5 gobars just to be sure.

Posted

i have actually heard that you do want a gap between the plate and the braces... no idea why because this is all new to me, but thats what i heard as well. And you shouldnt have do sand any radius into something 1/8 thin should you? even if it is maple, which mine is, it should conform to such a small radius

Posted

Personally, I tuck the edges of the bridge plate in to the legs of the X brace.

With regards to leaving gaps between things on the soundboard (though I don't agree that the bridge plate is a place to do it) it can be a good idea. Butt joints on a soundboard can sometimes be responsible for buzzes, hence on any intersection on my soundboards I either tuck into rebates, or chamfer the end of a brace to leave a small gap.

Posted

I simply butt tightly. I don't want to mess with a perfect fit on an inlet bridge plate, because I figure if I make the inlet too shallow, I get suboptimal bonding of the brace on the bottom, and there's less surface area on the main structural brace in the entire instrument (ie, the X). Then there's the fact that bridge plates on pinned bridge guitars do wear, and I don't want to build a guitar that's a major PITA to repair. That, and I've yet to actually hear anyone complain about buzzing with a good butt joint. I glue the X first, then the bridge plate pushing it into the X. You could always simply chamfer the edges contacting the X. Should take all of 10 seconds to do, no risk of buzzing.

Posted
I simply butt tightly. I don't want to mess with a perfect fit on an inlet bridge plate, because I figure if I make the inlet too shallow, I get suboptimal bonding of the brace on the bottom, and there's less surface area on the main structural brace in the entire instrument (ie, the X). Then there's the fact that bridge plates on pinned bridge guitars do wear, and I don't want to build a guitar that's a major PITA to repair. That, and I've yet to actually hear anyone complain about buzzing with a good butt joint. I glue the X first, then the bridge plate pushing it into the X. You could always simply chamfer the edges contacting the X. Should take all of 10 seconds to do, no risk of buzzing.

If you leave a gap, you want the plate to have less stress or spring, so you sand it to radius. Kinkead, Cumpliano. I have no Idea if it would effect a chiladni pattern with nodes and all. Why would you not radius? This craft is all about 1/100's of an inch and perfect joints. The radius gap on a 25' /bridge plate would be about 2 mm.

I also use thin flat gauges to test for a tight fit. Sanding to radius get me tighter than not sanding to radius. :D

Posted (edited)

1.8 to 2 mm.

As for radiussing...the bridge plate is thinner than the top, and that's not sanded to radius either, it's pushed into it. It's also, in that area, being held in shape by the tallest braces on the inside (the X brace) and the stiffest, widest, heaviest brace on the entire top (the bridge itself) on the outside. Also, 2mm span for a bridge plate in a 25' radius dome? Strikes me as way, way too much. It's only like 15 cm wide at its widest point.

Edited by Mattia
Posted (edited)
Also, 2mm span for a bridge plate in a 25' radius dome? Strikes me as way, way too much. It's only like 15 cm wide at its widest point.

25' radius; 15cm wide plate = 0.015" gap (0.375 mm)

Edited by Dave Higham
Posted
Also, 2mm span for a bridge plate in a 25' radius dome? Strikes me as way, way too much. It's only like 15 cm wide at its widest point.

25' radius; 15cm wide plate = 0.015" gap (0.375 mm)

Thanks for the math. That would actually be sandable...

Posted

Good luck sanding your 0.090" thick bridgeplate to a 25' radius. Just the slightest pressure from your finger tips will bend the plate and it won't sand out perfect. There will always be a gap of some sort, somewhere in the bridge plate to push down against the top plate.

Also, when clamping down the bridge plate, no one has mentioned using a clamping caul over top of it. If using the go-bars alone you get point loads only where the go-bars are (the bridge plate is to thin to distribute the load any real amount) so having a clamping caul of 3/4" MDF or plywood will distribute the load of the go-bars alot more through the bridge plate. Also if you go through the trouble of sanding the radius into the bridge plate, you better do it on the clamping caul too.

Posted

I put bars about every 1/4", so even if the pressure isn't evenly distrubuted, I think it's distributed more than well enough. The plate isn't under much tension or stress of any kind, after all, and the ball ends pull it closer in place. Although I guess making a caul would take all of about 2 minutes...

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