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How do YOU decide which side to join on tops and backs
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=22702		 Page 1 of 1
Author:  Dave Livermore [ Thu Jun 11, 2009 3:44 pm ]
Post subject:  How do YOU decide which side to join on tops and backs
All-
I've made enough guitars that I should know this. I always look at the grain, and put the tightest grain in the middle when I join a top or back.
But in looking at my current stash of wood, there are a couple sets that would LOOK much cooler if I joined what would be the outside (of the tree's) edges together in the center of a guitar.

Then I considered the instruments with sapwood center seams and that seems to go against the method I use.

So, what is the accepted method for deteriming which side to join?

Dave
Author:  StevenWheeler [ Thu Jun 11, 2009 3:52 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
My method on the tops is to put the tight grain to the center. The backs go together how I think they look the best.

Steve
Author:  Rich Schnee [ Thu Jun 11, 2009 5:19 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
Which ever way it looks esthetically pleasing.
Author:  Shane Neifer [ Thu Jun 11, 2009 5:33 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
For top sets, it is typically the "outside" of the tree that is tightest. That is also where the sapwood would be so joining the sapwood in the centre is consistent with joining the wood at it's tightest edge. Having said all of this I do occasionally get trees where the grain is very evenly spaced right across the top so there is the occasion where these sets may get joined opposite to convention, for instance to avoid a defect. Also, if you were to get very particular about your processes, there may one edge that is not quite as stiff as the other edge, would you want the stiff edge in the middle or out at the edge of the guitar.... idunno . That would all depend on your building style and philosphy.

Shane
Author:  Pat Foster [ Thu Jun 11, 2009 9:45 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
Whichever has the more vertical grain, which most often turns out to be the side with the tightest grain. If the side with the tightest grain had the more vertical grain, I don't know what I'd do, but I've never encountered that.

Pat
Author:  Bob Garrish [ Fri Jun 12, 2009 11:01 am ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
I go for whichever way looks best, with a strong bias toward having symmetry about the joint.
Author:  Dennis Leahy [ Fri Jun 12, 2009 1:41 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
If the pieces of wood are well quartersawn across the entire width of the board (a rarity in many species), then I would agree to just try both ways in a dry match-up and see which way looks best. Like Bob mentioned, I am a symmetry nut, and there is usually one edge that forms a "better" (more symmetrical) bookmatch. Sometimes, this may involve straight-lining the wood at an angle to the edge, to avoid a defect (this is where you'll be really glad you have made a clear acrylic or polycarbonate template.) I have started laying out a few defect-free back sets at an angle, both to give more interest to the straight grain (now forming sort of a chevron, rather than just parallel stripes), and then save the pair of angled cutoffs to form a bookmatched wedge for a faux 3-piece back that has a perfectly symmetrical wedge. See, I told you I was a symmetry nut!

Now, if the wood is well quartersawn at just one edge, and runs to rift or even flat on the other edges of the board, I would recommend (from a wood physics standpoint) that the quartersawn edges joined will make the back more stable. Radial (quartersawn) wood is always more stable (resistant to movement due to RH swings) than tangentially cut (flatsawn ) wood. I know that splash of flatsawn wood in the center sometimes looks cool, but I would resist the aesthetic urge to do that, and opt for stability.

Dennis
Author:  Alan Carruth [ Sat Jun 13, 2009 3:35 pm ]
Post subject:  Re: How do YOU decide which side to join on tops and backs
Runnout can also be an issue. Often a tree will start out with little or no twist, and corkscrew more and more as it gets bigger. Some species, notably Red spruce, will grow with 'stripes'; the twist changes as the tree grows. A quartered top cut along the axis of a tree that grows with a twist will have a noticable change in runnout across the center joint. Cutting from split billets allows you to at least get little or no runnout along one edge, but usually in that case the runnout will increase as you go across the top.

I had a top a year or so ago that was sold to me as 'Master' grade, and, indeed, it looked it. It's Euro spruce, with nice, tight grain that widens a bit toward the heart side, and some small bearclaw along the bark side. The only problem is that the tree had so much twist that the runnout got to be about 1:5 along the bark side. Joined that way the two lines of reflected light ran diagonally across each half of the top, and were displaced by about 4-5 inches at the join line. I cut it apart, and re-joined it along the heart side, where there was no runnout to speak of. The reflection line still runs diagonally, but at least it's continuous at the joint.

Runnout at the joint is both an structural and appearance problem. The appearance issue is obvious: the two sides of the top flash on and off independantly as you move the guitar. The structural problem comes in when the bridge lifts: it tends to peel off cleanly, and with less strength, on one side of the join, while the other side holds on like death, and tears into the top wood as it comes up.

Runnout decreases the long grain stiffness of the top , too, so a top with runnout would, in theory, need to be thicker to have the same strength and stiffness as one without runnout cut from the same tree. In this case, then, joining the top along the heart side to eleiminate most of the runnout not only made it look better, and work better as well (I believe).

That top, BTW, in on the plate tuning DVD: it's the one that gave me the most trouble. I'll have the guitar at Montreal, and you can judge whether the runnout hurt the sound or not.
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