Edge joining thin plywood?

[Dan]

Folks --

This question came up while looking at some old project plans. They were done up using cardboard mockups to get ideas of proportion and space.

Lots of these used the "sliding card" principle of assembly Notches in components would all slide and click together and you would get a useful object from a set of flat parts. The sliding method can wait for some other day......

What I found was that one idea for a basket/Tub involved joining thin ( 1/4 inch plywood ) I had thought that perhaps it would be better to fetch in some sheet metal and just pop rivet the edges together. However, a trip today thru the book store ( we have the school for american craftsman on the RIT campus ) I noticed one of the displays had been done using a nice grade of plywood butt jointed together and fastened with staples.

Any know of a good way to join thin plywood pieces?

--dan

[Chris Friesen]

How about glue? 1/4" is a reasonable width, but you'd want to have fairly accurate cuts.

Chris

[Scott Cox]

"Scarf" join them with opposing rabbets.

[Robatoy]

Luthiers butt-join pieces much thinner than that. As Chris pointed out, you'd want a good fit. A single pass with a 1/4" router bit (straight) along a fence, which cuts through both pieces at the same time (sometimes called a 'dutchman') will give you a perfect fit.

The joint will be stronger than the wood, if done properly.

[Father Haskell]

Traditionally done with a shooting board and plane. Fit is close enough that the pieces don't even need to be clamped, just rubbed and pressed together until the horse glue cools.

Joints in guitar bodies are usually reinforced by cleats or braces.

[Father Haskell]

Cut the joints straight and use yellow glue. The joints will flex before they snap. Clamp the panels together with a "mold," that is, a sheet of 3/4" ply with tacks around the panels less an eighth of an inch so that pressing down on the joint will force the panels together -- if your finished glueup is 12" wide, you'll have two rows of tacks on your mold board set 11-7/8" apart. Masking tape under the joint will keep the panels from gluing themselves to the mold.

[Leuf]

What kind of 1/4" ply? If it's 3 ply with thin outer plies and a thick center then you can make a decent glue joint so long as you have the grain of the outer plies perpendicular to the joint. If you've got 5 ply baltic birch with all the plies the same thickness then you'll get a better glue joint with the outer plies parallel to the joint.

Usually you have some kind of a back or bottom on the piece which provides a lot of strength to keep those joints from racking.

For something like a basket/tub, well I would probably make it like a drawer. Dovetail the corners and the bottom sits in a groove. But I wouldn't be using ply for the sides.

-Leuf

[Dave Gordon]

Thats a stepped scarf. Better would be a tapered scarf

glues make this a pretty strong joint.