Replies

1. 
   John_D | Mar 02, 2006 02:14am | #1

   You'll have much more strength if you add a skin below, and add some cross members, gluing both skins to the entire web.  This converts the shelf to a torsion box, an exceptionally strong construction with excellent resistance to sag and racking.  You can make it fit the same space by shaving some height off your 1x2's.

   If you're going to have these shelves installed so you can't see the ends, why not just butt them with pocket screws if you don't want to do a fancier joint?  If the ends will be visible, there are a lot of possibilities; a simple miter isn't difficult since you'll be batch-cutting 48 ends and 48 sides, and it'll be plenty strong as part of a torsion box.

   My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.
1. 
   skidkid | Mar 02, 2006 03:33am | #2

   John,

   You are a genius.

   I never thought of a simple miter at the corners; I was thinking of using glue blocks to reinforce the corners.

   Torsion box sounds good; I'll make up one sample and see how it deflects with 32 inch span while loaded; if deflection seems excessive I can reduce the span to 24 inches with an additional vertical support.

   The vertical supports are 7 feet high; also lightweight trusses from 1x2's with quarter inch plywood gussets.

   Cant use pocket screws; no jig; no screws; no money.

   Thanks,

   Hank.

    

    

1. 
   John_D | Mar 02, 2006 08:08am | #3

   Good luck.  I'll be curious how it comes out.My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.

1. 
   CraigC | Mar 02, 2006 03:56pm | #4

   This type of construction is very common in this part of the world - we call it tambor (drum), but not as in tambour.With regard to your question as to how to join the internal members, you can do butt joints with a staple gun - the glue on the both skins holds it all together. Here, for the sides & ends veneer is used with contact cement to finally give a 'solid wood' look.

1. 
   skidkid | Mar 02, 2006 04:26pm | #6

   Thanks.

   Dont have a staple gun; will use 3/4 brads.

   Hank.

2. 
   loucarabasi | Mar 09, 2006 03:57am | #7

   Hank, You will be very suprised how strong the shelves are when you laminate both sides of the shelf. I just made a lumber assembly rack and the shelves span 57inches and they are super strong.

   -Lou

3. 
   skidkid | Mar 09, 2006 02:46pm | #8

   Thanks Lou,

   I'm making tiny trusses from the 1x2's with triangles and will laminate both sides.

   This is very labor intensive but retirees have lots of time.

   Sure, you can use 3/4 baltic birch plywood; that was my first instinct but large offcuts are scarce at the landfill and I found parts of 3 roof trusses from a demo job; covered in nails and black paint; underneath all the gunk..........beautiful straight grain cedar.

   Thanks,

   Hank.

4. 
   AlanWS | Mar 10, 2006 02:45am | #9

   You really don't need triangles, since the skin serves the purpose of bracing it triangularly in lots of ways. They won't hurt though. Miters, half laps, or even butt joints in the 1x2 frame are probably strong enough with the skin holding it together. If the shelf is supported at the ends, I'd just make sure the long pieces extend full length, with crossbraces between them.

5. 
   skidkid | Mar 10, 2006 10:58pm | #10

   Thanks Alan,

   No triangles; how about 1 or 2 intermediate cross pieces ladder style, joints butted; miters in the corners of the perimeter; plywood both sides glued and 3/4 brads.

   The long pieces are 1 and 1/2 x 15/16; the balance are 1x2's all cedar.

   Hank.

6. 
   John_D | Mar 11, 2006 01:03am | #11

   For a torsion box to work well, you'll want to matrix throughout the structure.  Not sure of the optimal spacing, but I can't imagine you'd want to be more than about 5" x 5" for your individual cells.  A lot of your strength will come from the internal matrix being bonded (glued, possibly bradded too) to the two skins.My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.

7. 
   skidkid | Mar 12, 2006 12:26am | #14

   Thanks John,

   I'm going to start with the minimum structure req'd, test it for a while to watch deflection then keep adding to the structure if necessary until deflection is acceptable; a kinda experiment I guess.   Permanent deflection of say 1/4 inch at mid span fully loaded would be OK.

   You are right; I'll probably end up with a grid and 2 skins but I have seen hollow core doors with no grid; just a few cross pieces; granted not much load on an interior door.

   This will be the guinea pig; lots more lightweight shelving to do.

   Also I think the species and grade of the wood is important; mostly I find cedar and mahogany here; both imported; the local wood is all acacia; like planing cast iron.

   Hank.

8. 
   AlanWS | Mar 11, 2006 02:00am | #12

   How close together the cross braces should be will depend on how strong and rigid you need the shelf. Usually when people make a torsion box, they want something extremely strong and flat, probably much stronger than I think you are talking about. How strong your shelves need to be will depend on how you want to load them. For 30" shelves 10" wide, I suspect that a frame around the outside and two crosswise dividers within, faced on top and bottom with 1/4" plywood would hold a lot. Since you are planning to make quite a few, it might be worth the bother to make one the easiest way, and test it to see how strong it is before deciding whether to make a more elaborate version. Your shelves are beginning to sound like the stock cart Norm Abrams recently made to hold stock while working on a project: http://www.newyankee.com/getproduct3.cgi?0603

9. 
   skidkid | Mar 11, 2006 11:58pm | #13

   Never saw Norm's cart; be looking for a re-run.

   The plan is; make 1 shelf with plywood on top only; glued and brads at 4 inches o.c.; no cross pieces; mount it in place between supports and load it completely with heavy books; wait a few days and watch for deflection.

   The cedar frame is very strong in bending.

   If deflection is excessive; add 2 intermediate cross pieces and the other skin.

   I did use 3/4 inch plywood for shelves on another project and all of them were very good at resisting bending except one and I found that for some obscure reason I had the grain running front to back instead of left to right so I came to the conclusion that the outer skins should run with the long dimension.

   Still cutting parts.

   Hank. 

2. 
   skidkid | Mar 02, 2006 04:24pm | #5

   Thanks.

   Making an assembly jig for the layout.

   Hank.