What are the limitations regarding curving the top instead of carving? Does an exagerated induced arch breakdown over time?It seems a curved brace would hold. Just curious before I ruin good wood.......! Mandolas in mind....tailpiece.
Are you talking about bending the braces, the top/back or everything? I've seen plenty of curved tops and backs, all done in plywood. It's been pretty common in lower end arch top instruments for a long time. Somewhere in my reference material I have a print out of a process to heat and form thin solid wood tops that I got from a web site.If I remember correctly the man doing it used a plaster reverse mold and made the plates in 2 or 4 pieces then edged glued them to make the final plate. I'll try to find it and see if the site is still available.
The thing about carving a top/back is that you have the ability to graduate the thickness. I don't know how you would do this with a formed top. I suppose it is possible to mold plywood then graduate the thickness on the inside but I haven't see this and don't know how well it would work. I suspect that the different densities of veneer and the various grain directions may be a problem with that idea.
Several years ago I thought about trying to make a top plate out of strips of spruce that were bent to shape and edge glued together. I wanted to leave them thick enough that I could graduate it once it was glued up. I figured on making a reverse mold in foam and fiberglass. I finally realized that it was more work to make a mold then it would take to just carve the top. I also had trouble figuring out how I was going to get square edges on strips bent into compound curves so I would have good tight glue lines.
Besides all of that, I realized that I really like the carving process. I've only carved full plates a couple of times but I really enjoyed it.... that is, once I got my tools setup and sharpened properly. ( To me, half the battle is sharpening tools. Once I get past that, it all down hill. )
I don't know about curved/bent bracing. I'm not aware of having seen any used in arch top instruments. I think that carving the wood to fit allows it to move in all directions freely. Bending braces would pre-load or pre-stress the brace so that it would move more easily in some directions than in others. Could be that it's done all the time and I'm just not aware of it.
In the 20 or 30s they formed ,pressed tops for guitars and violins. I have seen backs for guitars also pressed. I don't remember if they were glued before or after. I do know they were solid wood so if it needed carved or thickness it could be done.
I have a large oven that could be used and have thought of making a form and pressing but never got around to it . the early 80s I got this crazy idea to bend and make a full body out of Formica and now Martin Guitars are doing so. I thought every body would call me crazy so I garbaged the sides and top and back. Guess I should have finished it.
I am thinking of making a clear plexiglass guitar with wood bracing.
Tim, are you talking about a "Flat top" instrument with some arching or an Arch top, carved instrument? I couldn't tell from your first post if you are discussing braces or carving plates, like for a mandolin or Arch top guitar. Now, with your mention of a 25 foot radius, it seems that you are talking about arching the back and top of a "flat top" guitar. Are you talking about Arch top instruments or arching a flat top instrument?
OK, now I understand. Most of what I've written was with the idea in mind that we were discussing carved arch top instruments like mandolins, violins .... I doubt if much of it applies to flat top instruments that have a bit of arch to them. Sorry about that.
I know a lot of flat top octave mandos & bouzoukis are down to as tight as 16' induced radius top and some even tighter. If you take a (spare!) piece of spruce & start to deflect it, it'll go quite a ways without breaking. The big 8 string instruments in flat top use the extra strength of the tighter radius to help counter the downward string pressure (i'm talking floating bridge with tailpiece style). I'm not touching the issue of what putting the top in stress does to tone though. In 'zouks Ive not had a problem but you are shooting for quite a different sound in a zouk vs. a geetar.
I've still got to find that article that I mentioned earlier. In it the guy was building bouzoukis and wanting to try some arched top models. What he's talking about would arch the wood enough to rival a carved top instrument but he seem to think the induced stress may not be such an issue in a bouzouki. I just don't know enough about them to know.