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Side braces - - - how many and how thick?
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50326		 Page 1 of 1
Author:  phavriluk [ Mon Feb 19, 2018 4:16 pm ]
Post subject:  Side braces - - - how many and how thick?
I'm scratchbuilding a pair of guitars, shrunken dreadnoughts, solid wood. I'm speculating on what I ought to be using for side braces, so that the sides will turn out generally flat. Sides being .075 thick, I haven't got a lot to spend to flatten the sides by scraping/sanding. So... I have a some cutoffs from the side profiles, these are .075" thick, I cut them into 1/4-inch strips. Are side strips .075 thick stiff enough for side supports? I can double them up and angle the outer edges (see Dana Bourgeois' guitars) if thicker would be useful. I've picked up the idea that spacing the side supports every three inches is common practice.

So...advice will be gratefully appreciated.

Thanks!
Author:  Ben-Had [ Mon Feb 19, 2018 5:38 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Peter, I use 1/2" wide x side thickness for the strips. I place them over the back braces (plus the two on the ends) simply because it provides the distance and number I want and I think symmetry has a nice look.
Author:  phavriluk [ Mon Feb 19, 2018 5:44 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Thanks, Tim. Much obliged.
Author:  J De Rocher [ Mon Feb 19, 2018 6:28 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
I don't have an answer to your specific question, but there was a good discussion of pros and cons of different approaches to side braces in this thread: http://luthiersforum.com/forum/viewtopic.php?f=10101&t=50109&hilit=side+braces
Author:  Alan Carruth [ Mon Feb 19, 2018 7:32 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
However many you use they should be notched into the liners. A wood cross brace that ends at the liner creates a stress riser at the joint. If the side takes a hit the force is concentrated at that end point, so that's where the side will crack; just where it's hardest to fix.

I use cloth tapes on the sides. They add some resistence to cracks starting, annd can stop them from running further along the side. With thin sides you might want to put one wood fillet across the side in the flat spot just below the waist, to reduce the likelihood of cupping there. Otherwise IMO tapes are better.
Author:  phavriluk [ Mon Feb 19, 2018 7:57 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Allan, I'll hold that thought. Not a whole lot of extra effort, and I can see where it would be a good idea to put the kerfing/side support intersection inside the plane of the kerfing where there's all that wood hanging around.

Thanks very much.
Author:  Ben-Had [ Tue Feb 20, 2018 6:20 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Alan Carruth wrote:
However many you use they should be notched into the liners. A wood cross brace that ends at the liner creates a stress riser at the joint. If the side takes a hit the force is concentrated at that end point, so that's where the side will crack; just where it's hardest to fix.

I use cloth tapes on the sides. They add some resistence to cracks starting, annd can stop them from running further along the side. With thin sides you might want to put one wood fillet across the side in the flat spot just below the waist, to reduce the likelihood of cupping there. Otherwise IMO tapes are better.

I probably should have added that they are not notched but the sides and ends are chamfered, hard to see in the photo. When I was taught I was told this was to reduce the stress riser.
Author:  phavriluk [ Tue Feb 20, 2018 7:01 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Here's what I ended up doing to fabricate the side supports: Stripped cutoffs from sides (.080 thick) into 1/4-inch-wide strips, laminated them together in pairs (total .160 thick) and angled the sides 45 degrees on one of the two pieces in each support, so that it won't look like a hunk of 2x4 stuck in the guitar, it'll be right artsy with the taper and all.

Tim, I noticed your mention of eighteen supports in the body in your picture. I'll do that on my first one and see if I've overdone the side supports or not.

I'm using reversed kerfing (solid strip visible inside the body), and I think there'd be no problem notching the kerf teeth to allow me to install the side supports all the way between top and bottom and still leave the continuous strip intact. We'll see. That would certainly help make the guitar useful in a bar fight.

Thanks, everybody.
Author:  Alan Carruth [ Wed Feb 21, 2018 4:55 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
My rule of thumb is that any brace that can't be tapered down in height to less than 1/3 the thickness of the piece it's glued to needs to be inlet. The taper has to be long enough to be flexible; a short chamfer is not enough. There are, of course, always exceptions: I chamfer fan brace ends on Classical tops, as per tradition, and have had no problems so far.
Author:  Bryan Bear [ Wed Feb 21, 2018 5:05 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
Alan Carruth wrote:
My rule of thumb is that any brace that can't be tapered down in height to less than 1/3 the thickness of the piece it's glued to needs to be inlet. The taper has to be long enough to be flexible; a short chamfer is not enough. There are, of course, always exceptions: I chamfer fan brace ends on Classical tops, as per tradition, and have had no problems so far.


Thanks! that 1/3 thickness is a rule of thumb I will have to remember. Too bad there isn't a convenient way to have a rule about how long the taper needs to be.
Author:  Ben-Had [ Wed Feb 21, 2018 11:53 pm ]
Post subject:  Re: Side braces - - - how many and how thick?
phavriluk wrote:
Tim, I noticed your mention of eighteen supports in the body in your picture.

Twelve actually Peter. Six on each side. One over each of the four brace ends and one centered on each end between the block an brace.
Author:  Mike OMelia [ Thu Feb 22, 2018 5:32 am ]
Post subject:  Re: Side braces - - - how many and how thick?
Hmmm. I've never quite thought about it from a symmetry point of view. Maybe I should.
Author:  phavriluk [ Thu Feb 22, 2018 9:58 am ]
Post subject:  Re: Side braces - - - how many and how thick?
That's a nice and straightforward way to locate the side supports. Thanks!
Author:  Bryan Bear [ Thu Feb 22, 2018 10:58 am ]
Post subject:  Re: Side braces - - - how many and how thick?
I usually put them in the flattest spots; the curves are very strong. I run them full height under the linings. I try to have them NOT line up with any of the braces, only because it is harder to notch the linings to inlet the braces if I have to cut side grain linings and endgrain reinforcements with my chisel. Is there an advantage to having them support the braces that I have not considered?
Author:  jfmckenna [ Thu Feb 22, 2018 11:54 am ]
Post subject:  Re: Side braces - - - how many and how thick?
This is why if you do use side struts you want to notch them or at least taper. I personally don't use them any more unless necessary like for example very thin sides.

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