This video is perfect timing! I'm putting a solid back on my mini jumbo. It had an arched laminate back before and the arch was steamed pressed. My first attempt I didn't brace the back to the edges and cracked it. I can repair the crack, but will have to make new braces that go from edge to edge. I didn't brace the new back edge to edge because I was concerned about how the back would not fit flush with the kerfing due to the slight radius. How to you deal with this issue when gluing the back on--a slightly curved surface of the back to a straight surface of the kerfing? thanks, Jeff PS I've discovered how much stronger laminate is.
Hi Jeff, If you try to glue a radiused back onto a flat rim, or a rim that does not match the radius of the back then you are going to run into problems. Either you won’t get a clean glue joint, or if you clamp it down firmly then you will end up with stress along the joint which will likely lead to cracking. The proper way is to sand the back of the rim to the same radius as the arch in the back. This is done with a radius sanding dish. The rim is sanded so that it has a matching radius to the back. This way you get a proper glue joint without the stress of forcing the wood into place. I hope I understood your question correctly.
Yes, you understood it perfectly. I've discovered the importance of a radius dish for the rim. I think the video I watched on radiusing the braces may not have explained that. The back is arched quite a bit from the top to the bottom and the solid back is being stressed both top to bottom and now side to side. I will need to reduce the arch to almost nothing and brace the new back to the edge. I may even run 2 small popsicle braces down the back to support that top to bottom arch. This is my first back replacement and I knew there would be many lessons ahead. Thanks for taking the time.
Hi Jeff, Sorry I missed this last comment. I'd have to check the exact thickness, but off the top of my head I think it is around 3/32" for the centre strip.
Hi Josh! I'm thinking of replacing a spruce top guitar with mahogany. I have some "sinker mahogany" which is a little more dense. Do u have any thoughts on how sinker would sound on a guitar top compared to standard mahogany? Thanks, jeff
Hi Jeff, I don't expect you'll notice a big difference between a regular mahogany top and the sinker. If anything the lighter regular mahogany may be a bit more responsive and give you a little more volume. But again I expect the difference would be very small. The difference between spruce and mahogany is very noticeable, but I'm assuming you have tried out some mahogany top guitars so that you know what sort of sound you are going to get.
Thanks! I'm going to try 1/16" for a little more flex.
Great video Josh. Are your backs and tops flat - is the deck platform not radiussed?
Hi Zohn, All my backs have a 15' radius. The curved braces are glued in a rectangle radius work-board which shows up around minute 13 in the vide.
This video is perfect timing! I'm putting a solid back on my mini jumbo. It had an arched laminate back before and the arch was steamed pressed. My first attempt I didn't brace the back to
the edges and cracked it. I can repair the crack, but will have to make new braces that go from edge to edge. I didn't brace the new back edge to edge because I was concerned about how the back would not fit flush with the kerfing due to the slight radius. How to you deal with this issue when gluing the back on--a slightly curved surface of the back to a straight surface of the kerfing? thanks, Jeff PS I've discovered how much stronger laminate is.
Hi Jeff, If you try to glue a radiused back onto a flat rim, or a rim that does not match the radius of the back then you are going to run into problems. Either you won’t get a clean glue joint, or if you clamp it down firmly then you will end up with stress along the joint which will likely lead to cracking. The proper way is to sand the back of the rim to the same radius as the arch in the back. This is done with a radius sanding dish. The rim is sanded so that it has a matching radius to the back. This way you get a proper glue joint without the stress of forcing the wood into place. I hope I understood your question correctly.
Yes, you understood it perfectly. I've discovered the importance of a radius dish for the rim. I think the video I watched on radiusing the braces may not have explained that. The back is arched quite a bit from the top to the bottom and the solid back is being stressed both top to bottom and now side to side. I will need to reduce the arch to almost nothing and brace the new back to the edge. I may even run 2 small popsicle braces down the back to support that top to bottom arch. This is my first back replacement and I knew there would be many lessons ahead. Thanks for taking the time.
Hi Josh!
How thick a strip of spruce do u use for back bracing(longitudinal).
Hi Jeff, Sorry I missed this last comment. I'd have to check the exact thickness, but off the top of my head I think it is around 3/32" for the centre strip.
Hi Josh! I'm thinking of replacing a spruce top guitar with mahogany. I have some "sinker mahogany" which is a little more dense. Do u have any thoughts on how sinker would sound on a guitar top compared to standard mahogany? Thanks, jeff
Hi Jeff, I don't expect you'll notice a big difference between a regular mahogany top and the sinker. If anything the lighter regular mahogany may be a bit more responsive and give you a little more volume. But again I expect the difference would be very small. The difference between spruce and mahogany is very noticeable, but I'm assuming you have tried out some mahogany top guitars so that you know what sort of sound you are going to get.
Thanks! That helps.