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  #46  
Old 10-25-2013, 05:24 AM
Ned Milburn Ned Milburn is offline
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Quote:
Originally Posted by Left of Sam View Post
QUESTION!

- so I have back radius but there is also taper in the sides. Do people usually glue the back strip brace in the form of the side taper?


Thanks. Sam
I don't understand the question. Sides taper vertically and have nothing to do with the back center strip. Do you mean the center strip, or something else??
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  #47  
Old 10-25-2013, 09:33 AM
Sam VanLaningham Sam VanLaningham is offline
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Originally Posted by Ned Milburn View Post
I don't understand the question. Sides taper vertically and have nothing to do with the back center strip. Do you mean the center strip, or something else??
Sorry Ned! I am not sure of the name of the brace that runs longitudinally down the center of the center of the back?

So, let me try to clarify. The taper on the sides means that the back will have to be bent to follow the taper when glued on. Thus, when people glue on the longitudinal back brace before the back is ready to be joined to sides, do they take into consideration the bend that will happen because of side taper? FYI this still seems potentially confusing but I hope I've communicated better!

Thanks. Sam
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  #48  
Old 10-25-2013, 09:58 AM
charles Tauber charles Tauber is offline
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Originally Posted by Left of Sam View Post
Thus, when people glue on the longitudinal back brace before the back is ready to be joined to sides, do they take into consideration the bend that will happen because of side taper?
Short answer: for most people, no. It is a thin, non-stiff reinforcement of the center gluing seam, not a brace as such. Usually/often, the reinforcement is made with the grain running perpendicular to the seam, offering little stiffness while maximizing its ability to reduce splitting.
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  #49  
Old 10-26-2013, 05:12 AM
jeff crisp jeff crisp is offline
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If you're not using a decorative centre strip on the outside of the back and the joint is clean its probably not needed. Though people often expect to see them so I always put one in.
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  #50  
Old 10-26-2013, 02:44 PM
Sam VanLaningham Sam VanLaningham is offline
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Quote:
Originally Posted by charles Tauber View Post
Short answer: for most people, no. It is a thin, non-stiff reinforcement of the center gluing seam, not a brace as such. Usually/often, the reinforcement is made with the grain running perpendicular to the seam, offering little stiffness while maximizing its ability to reduce splitting.
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Originally Posted by jeff crisp View Post
If you're not using a decorative centre strip on the outside of the back and the joint is clean its probably not needed. Though people often expect to see them so I always put one in.
Thanks guys! Good info. I'll go with just glueing it flat.

Sam
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  #51  
Old 10-29-2013, 04:06 PM
Sam VanLaningham Sam VanLaningham is offline
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Hi everybody - Do any of you have an opinion on top thickness for Engelmann spruce?

I searched around but didnt see anybody suggesting different-than-standard thicknesses. I did however find one interesting anecdote from a guy who built three essentially identical 00's with engelmann, sitka, and adirondack tops and said each top was around 0.100". He thought the Engelmann was by far the "best" sounding, being more open than the other two. Soooo, is 0.100" ideal or too thin if I'm going with the typical adi-braces for a L-00?

Any thoughts?

Sam

Last edited by Sam VanLaningham; 10-29-2013 at 04:11 PM.
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  #52  
Old 10-29-2013, 05:29 PM
Jim.S Jim.S is offline
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Is it ideal or too thin? That will depend on a few things, one being your target. As you don't really have a target other than to build a guitar then it will probably be fine. When you mentioned the sitka, adi, englemann scenario what is likely to be happening there is that in general sitka and adi are stiffer than englemann at the same thickness so at 0.1" that englemann top was less stiff and perhaps a little lighter than the other two creating a more efficient top. That is more monopole mobility and faster acceleration that could give the impression that the englemann was the "best" of the three (if the adi or sitka been taken to 0.08" then the outcomes may have been similar). When it comes to hand building there is no "standard" thickness, each individual piece of wood is treated differently so to tell you 0.1" is fine is too hard to do cause if your bit of englemann is a particularly weak bit then it may be too thin or may not depending on you bracing size etc. For your first guitar building with the method you are using you really just have to go for it and see what happens (choose in the region of what others use and you will be fine).

Jim
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  #53  
Old 11-07-2013, 07:14 PM
Sam VanLaningham Sam VanLaningham is offline
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Quote:
Originally Posted by Jim.S View Post
Is it ideal or too thin? That will depend on a few things, one being your target. As you don't really have a target other than to build a guitar then it will probably be fine. When you mentioned the sitka, adi, englemann scenario what is likely to be happening there is that in general sitka and adi are stiffer than englemann at the same thickness so at 0.1" that englemann top was less stiff and perhaps a little lighter than the other two creating a more efficient top. That is more monopole mobility and faster acceleration that could give the impression that the englemann was the "best" of the three (if the adi or sitka been taken to 0.08" then the outcomes may have been similar). When it comes to hand building there is no "standard" thickness, each individual piece of wood is treated differently so to tell you 0.1" is fine is too hard to do cause if your bit of englemann is a particularly weak bit then it may be too thin or may not depending on you bracing size etc. For your first guitar building with the method you are using you really just have to go for it and see what happens (choose in the region of what others use and you will be fine).

Jim
Jim, thanks a billion. These words helped guide me so I appreciate it!
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  #54  
Old 11-07-2013, 07:21 PM
Sam VanLaningham Sam VanLaningham is offline
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Ok, glueing in braces in my awesome go bar deck and radius dish (hehe). Anyways, seems to be working. I'm starting to figure out that there are many ways to do this and that the ultimate decider on my methods will be what I hear and feel on the other side!



Guess what else I learned: having a back that is too thin, making all sorts of minor adjustments and fixes because of that (backstrip alignment, cutting out shape too close to one edge, not fixing blemishes because it's already too thin etc etc) just leads to a likely meltdown at some point, as evidenced by the failed back you see here! I put so much EXTRA work into this because it was borderline and then it broke from very little disturbance (it was as thin as 0.06" in some spots.....I know!). So I don't think I'll try to make somethjng borderline work again. I'll just get it right from the start

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  #55  
Old 11-13-2013, 05:22 PM
Sam VanLaningham Sam VanLaningham is offline
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Ok top and (new) back braced up and rough shaped up. Fun fun fun!

The tap tone of the back is a lower pitch than the top. That isn't normally how a top-back is on a built acoustic. Is this normal for unattached tops/ backs?

Thanks for looking!

Sam




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  #56  
Old 11-13-2013, 07:07 PM
charles Tauber charles Tauber is offline
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Sam,

Abrupt changes in cross section create stress concentrations or stress risers. The abrupt change in height of your brace ends are stress risers. These should be avoided to resist the braces splitting at the abrupt change or having the brace ends come loose.
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  #57  
Old 11-13-2013, 07:54 PM
Sam VanLaningham Sam VanLaningham is offline
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Originally Posted by charles Tauber View Post
Sam,

Abrupt changes in cross section create stress concentrations or stress risers. The abrupt change in height of your brace ends are stress risers. These should be avoided to resist the braces splitting at the abrupt change or having the brace ends come loose.
Shheeeeeite.....you are meaning the ends of each brace? I dont need to redo, right? Just taper them more? Thanks for checking up on me!
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  #58  
Old 11-13-2013, 09:18 PM
charles Tauber charles Tauber is offline
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Originally Posted by Left of Sam View Post
Just taper them more?
Essentially, yes. Avoid abrupt changes where possible. Also, keep in mind that the plates (top and back) are very stiff at their edges due to their attachment to the sides. Also, the stiffness of the braces you add is proportional to the cube of their height. That is, small changes in height produce large changes in stiffness.

Typically braces taper gradually towards their ends in a concave-up curve to reflect that. Your top braces end with a fairly abrupt convex curvature maintaining the stiffness of the brace until very close to the edge, where the added stiffness isn't needed and may inhibit movement of the top. Taylor, as one example, puts a groove all around the inside of the lower bout of the top to increase flexibility - decrease stiffness - at the edges of the top. Many makers gradually feather the thickness of the top towards the edges for this same reason. Of course, this is done in conjunction with the shaping of the braces.

Here are a few illustrative pictures showing fairly typical shaping of the ends of the braces:





Also keep in mind that you are juggling weight (mass) and stiffness. Making things wider, but not taller, adds weight in greater proportion to adding stiffness. That is, double the width of a brace, it is twice as heavy, twice as stiff; double its height and you have twice the weight, but 8 times the stiffness. A rectangular cross section adds significantly more weight than a triangular one of the same height, but about the same stiffness. Thus, shaping the braces to be rectangular, but with rounded corners adds much more weight than making them more triangular, more peaked.

Keeping this in mind, unless your back is very thin, the reinforcement probably doesn't need to be that thick or that rectangular. Rounding it in cross section to remove the corners will reduce weight.

Last edited by charles Tauber; 11-13-2013 at 09:37 PM.
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  #59  
Old 11-13-2013, 09:29 PM
Jim.S Jim.S is offline
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The scalloped one seems popular Sam.



Jim

Edit. Charles is quicker on the draw.
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  #60  
Old 11-14-2013, 09:25 AM
arie arie is offline
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your back reinforcement strip is a bit "stout". no harm, and nothing needs to be done, but in the future you could trim that down to 1/2 of what you have now.

here's an example:




the strip isn't a brace as commonly thought but merely an extra cross grain glue surface for the two halves of the back plate.
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