What type of joint? - joining 5" x 8' x 5/16" cedar along the 8' edge

[John Poole]

I have Port Orford Cedar boards that are 5" wide, 8' long and 5/16th thick -- they are remnants from milling some 1"+ stock out of 1 1/2" thick decking. I want to join the boards to create a 3' wide backing for a bookshelf.

Lap joints? Or is there a better joint for thin soft woods? I figure a 5/8" lip on each of the laps would give a good adherence area for the glue.

Here's a drawing of what I'm thinking:


207201

Comments or suggestions?

[Dave Zellers]

Yes, shiplap;

No, glue.

Love Port Orford cedar. Awesome wood.

[Peter Quinn]

If you leave them as single boards they can be gapped slightly to leave room for wood movement. If glued together they move as one large board, not the best strategy for a case back unless itis plywood. So vote #2 for yes shiplap, no glue.

[glenn bradley]

I do three board backs like so; the two outer boards capture the middle board. For orientation, the first pic shows the 'inside' surface down. A bead on the show side of the center board's edges makes a nice detail. Outer edges are captured in a groove.

[phil harold]

I would vote tongue and grove and no glue

shiplap will not stop the boards from warping/curling

[Dave Zellers]

Normally I'd agree, but the boards are only 5/16" thick.

[Dave Gaul]

Normally I'd agree, but the boards are only 5/16" thick.

I'm currently working on a project which inlcuded joining some 5/16" material. I'm using a 3/32" slot cutter to make the groove, and have a shaker style rail & stile bit set for the tongue. I would think this type of setup would work fine for your application, since it is just for the back and not structural.

[Myk Rian]

I would also go with tongue and groove, for the reason already stated. Warping.

[Jerome Hanby]

That was my first thought too.


I would vote tongue and grove and no glue

shiplap will not stop the boards from warping/curling

[Kent A Bathurst]

I would vote tongue and grove and no glue

shiplap will not stop the boards from warping/curling

One "yeahbut".........Yeah, but...I have used shiplap on repro Stickley bookcases. My shelves are fixed [stopped dado into the sides], because I just don't like moveable shelves. There is a screw driven through the the center of each shiplap board into the 3 shelves. No warp.

[Terry Beadle]

I would use ship lap, no glue but I would not leave the backing pieces 8 foot long. Put some cross members in about every 15 ~ 20 inches. The shorter ship lapped boards will have less tendency to warp. Mount them in 3/16 ths slot dado's in the cross members. That will really give you the best chance against thin stock warping and add a great deal of structural strength to the book case.

[John Poole]

Thank you, all, for the suggestions. I think I'll try some prototypes;the tongue and groove is dicey given the thin and soft stock I'm working with... but, Port Orford Cedar does handle well, so I'll have to try some router/shaper cuts.

I really like the suggestion of Beadle's about having horizontal members every 15-18 inches thus limiting the length over which warpage may occur.

[Nick Canzona]

I think the stock is too thin for T&G, especially in wood this soft. I vote for shiplap--no glue. Last year I built a set of exterior doors for a deck project. Each door was 32Wx66H. I built and hung frames from yellow pine (painted), then applied cedar planks vertically for the outside face. Each plank was 5x66x1/2, with a 3/8" shiplap. When fastening, I used finishing nails, one row of which was about 1" from the overlapping edge, the second row about 1-3/4" from the underlapping edge. Deck stain finish. One winter and one very hot and wet summer with no problems.

[Pat Barry]

I wonder if the material is too thin for the shiplap also - its on 5/16 thick - that will give about a 1/8" lap . Make this dimension of any significant width and couple this with the fact its cedar and I think its likely to fail after a few books are pushed into place. I think the idea of reinforcing the boards by screwing into the fixed shelves is appropriate. Why couldn't you edge butt the pieces (no glue) and overlap a backer part to cover the seams. The backer would be invisible on the finished project.