Replies

1. 
   AlanWS | Mar 26, 2008 10:15pm | #1

   In plywood, where the grain runs in different directions in different layers, you generally want to have an odd number of layers for balance,so it won't warp. With a bent lamination where the grain all runs in the same direction, I can't see any reason that it would make any difference if the number of layers is even or odd.

   (It's the balance, not the odd number that's important even with plywood, since flooring underlayment frequently has an even number of plys so that the center two will form a strong tongue for the tongu and groove plywood edge.)

1. 
   JohnWW | Mar 26, 2008 11:03pm | #3

   In plywood with an even number of plys, at least two of the inner layers are glued to each other with the grain running in the same direction, that is what is done in the T&G. The two layers are still stronger than a single one and it avoids having a flaw in a single layer excessively weaken the tongue.John White

1. 
   AlanWS | Mar 27, 2008 04:11am | #6

   That is what I was trying to say. Thanks for the clarification.

2. 
   colebearanimals | Mar 26, 2008 11:00pm | #2

    

             Doesn't matter. Use any number of layers you want. Actually, plywood has odd layers only because that's what works out when the outer layer grain direction is the same. Stability isn't a factor.

                                                               Paul

3. 
   9619 | Mar 27, 2008 02:44am | #4

   Quickstep,

   I studied mathematics for six years.   If a mathematician woodworker was to answer your question in a theoretical fashion, he would say that as the number of laminations approaches infinity, the benefit of having an odd number of laminations approaches zero. 

   You got better advice from the other responders (and faster too).  I am just noodling aroung Knotsworld having fun for a few minutes.

   Mel

   Measure your output in smiles per board foot. 

1. 
   81treehouse | Mar 27, 2008 07:25am | #8

   And as the number of laminations approach zero, the likelihood of having an odd number of laminations approaches infinity.  <grin>

   Just lurking around.

    A bad day woodworking is better than a good day working -- yes, I'm retired!

2. 
   chuckh | Mar 27, 2008 07:27pm | #11

   It appears that the more laminations you have, you have an even chance of someone odd responding to your post. :-)

   Noodling at lunchtime,

   -Chuck

4. 
   sapwood | Mar 27, 2008 04:11am | #5

   I don't know what the banjo gods have been drinking. When doing bent lamination work where all the lams have grain running the same direction, the greater the number the better the overall product. Thinner laminations bend easier, and the greater glue surface means the bend will be more permanent (less springback). Odd or even numbers of laminations doesn't make a difference when all the grain runs parallel. In plywood, its another story.

   Perhaps the banjo gods are more concerned with the visual look rather than how the thing behaves.

1. 
   Quickstep | Mar 27, 2008 05:40am | #7

   From what I understand, the banjo guys believe that the amount of glue in the layup dampens the sound. The more joints, the more glue, the more adverse affect on the sound. Lower end banjos are often laid up of 22 layers of 1/32" veneer and are considered to be of lower quality. I don't think my ear, or my playing ability could discern the difference between 3 lams or 4 :)

1. 
   [email protected] | Mar 27, 2008 10:08pm | #12

   That would be true only if the glue is less stiff than the wood, and you have enough there to uncouple the vibration.  I can see that possibly being the case with yellow or white glue.  But not with most of the others. 

   The polyurethanes, like gorilla glue, could be a real problem if the clamp pressure was too low, and you ended up with foam between the layers.  But, with good clamping pressure they get stronger, and stiffer, than lignen, and wouldn't be a problem. 

    

5. 
   MikeHennessy | Mar 27, 2008 02:09pm | #9

   Ignore what those gurus are telling you. Just use some nice honduras mahogany, about 1/8" thick. Just one layer. Put a mahogany back on it too. Oh, and bend it kind of squiggly instead of round. And use a nice adirondack spruce top with a hole in the middle instead of that nasty hide stuff. And use 6 strings instead of 5. Guaranteed better sound.

   ;-)

   Mike Hennessy
   Pittsburgh, PA

1. 
   Quickstep | Mar 27, 2008 03:01pm | #10

   I've got those :) I'm branching out!