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Wenge sides cupping?
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=12933		 Page 1 of 1
Author:  Tim McKnight [ Mon Jul 23, 2007 11:29 am ]
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Has anyone exoperienced any problems with Wenge sides cupping? I bent a set a few weeks ago and when they came out of the bender they were nice and flat. I then laminated them and they were cupped after I removed them from my clamping form. I use solvent based glue so it wasn't water induced. This is the first set of sides that have done this after laminating them. Strange ???
Author:  Pwoolson [ Mon Jul 23, 2007 11:32 am ]
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Tim, not sure of an answer but what about throwing the whole laminated set back in the bender and run it through a couple of cycles. Hot enough to make the glue creep. Then let it cool under preasure in the bender.
Author:  John Mayes [ Mon Jul 23, 2007 12:17 pm ]
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We use Wenge quite often here at McPherson and never have I noticed any
cupping, in fact it seems to be a very, albeit splintery, wood.
Author:  Don Williams [ Mon Jul 23, 2007 12:33 pm ]
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Tim, what did you laminate the wenge to?
Author:  johno [ Mon Jul 23, 2007 10:32 pm ]
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I think Don is ont to something,

Remember the bi-metal springs. If these 2 different woods are expending and contracting at different rates (esp) across the grain,

<<<<<<>>>>>>>
>>>>>><<<<<<<

Whacha think would happen in that scenerio?
Author:  johno [ Mon Jul 23, 2007 10:38 pm ]
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Yea I know ... expanding, not expending. Sorry and while I am at it ... scenario not scenerio.

OOOOPPPs
Author:  Michael Dale Payne [ Tue Jul 24, 2007 12:47 am ]
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I have not done any laminated or double sides. But I seem to remember something from my grandfathers cabinet shop. It seamed to me that when possible he always laminated with the grains running perpendicular to each other to ad strength but I believe also to eliminate unwanted movement.

I know this is not a practical option as bending a side set with the grain perpendicular to the bends would be near if not totally impossible.
Author:  Pwoolson [ Tue Jul 24, 2007 12:52 am ]
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[QUOTE=MichaelP] I have not done any laminated or double sides. But I seem to remember something from my grandfathers cabinet shop. It seamed to me that when possible he always laminated with the grains running perpendicular to each other to ad strength but I believe also to eliminate unwanted movement.

I know this is not a practical option as bending a side set with the grain perpendicular to the bends would be near if not totally impossible.[/QUOTE]
Actually MP, it makes things easier. I do this on my side port support patch. I run cross grained spruce in there and it bends like a dream when there is another piece supporting it. Though you are right that it would be quite impractical because you'd have to have a 32-32" radius tree to get cross grained wood from but I think it makes some sense.
Author:  Tim McKnight [ Tue Jul 24, 2007 2:49 am ]
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Paul, I will try reheating and see what happens. I layed the laminated side sets aside and they probably would have ended up as BTU's this winter.

John, I used EIRW for the inner side. Grain is parallel with the outer (Wenge) side. Although it sounds like the right thing to do (running the inner lam at 90*) it just isn't practical. Even though both sides have the grain oriented in the same direction the completed side is extremely rigid.

The strange thing is the sides were dry when I started, came out of the Fox bender nice and flat and then cupped after laminating them. The outer caul on my laminating form is 1/8" thick and holds the wood very tightly iagainst the inner form while the epoxy sets over night. I have never experienced this before and thought it may have something to do with Wenge.

Thanks for the input guys.
Author:  Dennis Leahy [ Tue Jul 24, 2007 4:58 am ]
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Hi Tim,

Back in my days in architectural woodworking, I occasionally had to make some plywood (all veneers), and many times laminated veneer over a substrate. Generally, it is done with an odd number of plys: a stable core ply, and mirror matched plys on both sides of that core. A 3-ply plywood with an MDF core was about the only time we didn't need to worry about alternating the grain on the plys. So, I would think in terms like Wenge/Poplar/Wenge veneers, with the Poplar grain direction running opposite the Wenge veneers. That inside lam of Wenge might not be practical (or might be cost prohibitive) in guitarmaking, but that was the way we always did it for 3 ply all-veneer plywood. (With thicker core material, you can put a different species on the non-show face.) I remember other instances of having custom veneer "skins" made for us, and if they had a different species on the back, the skins would often curl. If AAA birdseye was used for the show face, then plain flatsawn hard maple could be used on the back, but it had to be either both quartered or both flatsawn for the outer plys.

I don't know if that is helpful or not, or whether 2 ply with the same or different species is standard procedure in laminated guitar sides. If that is the case, then the narrow width and gluing into a curved shape must be the secret to success, with the occasional failure due to some mismatch of moisture content, annular ring orientation, or shrinkage values. (I'm guessing.)

p.s. I can't wait to play one of your Hickory guitars sometime! I'm from northwest Ohio, and my childhood home was surrounded by Shagbark Hickory trees.
Author:  phil c-e [ Tue Jul 24, 2007 5:02 am ]
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tim,
i'm a rookie with one wenge experience - so take this into account big time.

i'm just finishing a wenge guitar where i laminated a maple venear on the inside. by venear, i mean venear. the stuff that comes in a roll and is applied to substrates with contact cement by the furniture/cabinet industry. contact cement is what i used for the lamination and i experienced no cupping of the wenge.

i know all of you builder types are wincing about my use of contact cement. i've done four guitars this way and have had good results. the sides become way stiffer, and the tone of the guitars has been great. that said, these will be my last laminated sides until i get set up to use the proper glue for the job. contact cement never turns rock hard, and so is not ideally suited to instrument making. still, it's been an easy way for me to dabble in double sides, and been enough of an encouragement for me to get serious about it down the road.

again, no cupping with the wenge, though the wood is pretty quirky in many other respects. the way things are panning out, though, the beauty of the stuff under finish is making it worth it.

phil
Author:  Barry Daniels [ Tue Jul 24, 2007 7:02 am ]
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Tim, were the wenge and EIR stabilized to your shop humidity? If one of them was a recent acquisition, that could have caused enough moisture content differential to lead to the cupping.

I laminate sides with urea formaldehyde glue and I only get cupping if I turn one of the inner plys 90 degrees. I use a .050" outer layer with a couple of .023" veneers.
Author:  Barry Daniels [ Tue Jul 24, 2007 7:04 am ]
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If moisture is the problem, you could moisten the concave side with water and it would probably flatten somewhat.
Author:  Alexandru Marian [ Tue Jul 24, 2007 8:25 am ]
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Is it really necessary for the inner layer to be one piece ?  It can be cut in squares, each rotated 90 degrees if one really must have them this way. But it is tedious to say at least.  
Author:  Don Williams [ Tue Jul 24, 2007 9:32 am ]
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As John Osthoff said, whenever you laminate two pieces of wood with different coefficients of expansion, you risk cupping. Add to that improper grain oriention, and you have a double-whammy. Dennis makes a good point with the 3-ply concept. This is what makes plywoods stable, having stable inner cores, and then outer layers where the grain is oriented to expand in opposite directions to counteract each other.

Another factor I've found with resawing woods is that you want to have both faces of a thin piece of wood to have the same surface type. In other words, if one side is sanded smooth, and the other side is a little more rough, you risk greater moisture loss or absorption with the rougher side due to more surface area exposed.
Author:  TonyKarol [ Tue Jul 24, 2007 9:57 am ]
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A great cabinet maker always used to say - do to one side of the wood whatever you do to the other ... thats why even MDF core ply or even cutsom table tops ahve veneer on the undersides as well .. it counteracts the moisture differentials effects - warping. IME wenge has been very stable, just tough to bend and splintery. I think you had wood that was not at the same moisture content Michael ...

All that said, I had a very curly piece of koa to bend into a florentine .. even at .080, and not a super tight curve, it wouldnt go without starting to split ... so I thinned to about 60, and then bent - OK, couple small edge lifts, but good enough. Then using the same solid bending form, titebonded a .030 veneer to the inside - stiff as can be and NO warp ... go figure - but the curvature certainly helps in this case as well.
Author:  TonyKarol [ Tue Jul 24, 2007 9:58 am ]
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Oops .. sorry Micheal, should have had Tim's name in there ... my apologies.
Author:  Tim McKnight [ Tue Jul 24, 2007 12:48 pm ]
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Both the Wenge and EIR have been in my wood room for at least two years. I have laminated dozens of side sets now and none have even hinted at distorting. All sides were sanded to 150 grit on my wide belt sander. I use the same bending and laminating process and adhesive on all my side sets and I have often used dissimialr woods inside and out.

It could be related to different coeficiencies of expansions. Since this is my first experience with Wenge I thought maybe I was missing something. Sounds like Wenge has beeen very stable and successful for the majority.

Another thought I had was maybe the humongous pores of Wenge allowed it to absorb more adhesive than the EIR and possibly more contraction as it hardened deep in the Wenge pores??? However, I have laminated Hickory without problems but it isn't quite as porous as Wenge.

Thanks again for the suggestions.
Author:  Bobc [ Tue Jul 24, 2007 1:16 pm ]
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Tim you may be on to something with the pores of the Wenge holding much more glue than the EIR. I haven't tried laminating sides myself but if and when I do I will use the same wood inside and out with a cross grain veneer of a stable wood like poplar in the center as Dennis has suggested. Maybe something like .035, .020, .035 if I ever find the time.
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