How do you guys join 6mm (1/4") ply?

[Ty Williams]

I’m building some shelf-ettes to put into an exiting Ikea Kallax unit so that I can “double-stack” my CDs on top of each other to make more efficient use of the space and store twice as many CDs. I’m planning on making them out of 1/4” (6mm) baltic birch ply because I want to waste as little space as possible with the structure of the insert. What I can’t figure out is how to join 6mm ply to itself. It’s just so thin! I can’t Domino it and my smallest pin nailer is still 18ga (which I’m afraid will blow out the ply). I’m not wild about relying on gluing ply end/side grain to face veneer ether.

How do you guys join stuff this thin for a quick-n-dirty project?

[Jamie Buxton]

So you're making something with two 1/4" shelves, and many vertical dividers running between the two shelves? If so, run shallow dados on the top of the lower shelf, and matching ones on the bottom of the upper shelf. By shallow, I mean maybe a sixteenth. You're just trying to locate each divider for glue-up. Glue in the dados is what holds the whole thing together.

While these joints do have some end-grain to face-grain joints, they also do have some face-grain to face-grain joints, and they will hold together.

But one other issue... If I'm right in understanding your plan, you're going to be making shelves that aren't very thick, and loading them with CDs. I'm not clear about how many CDs per shelf you're storing. But if it is a bunch, you're likely to see sagging.

[Ty Williams]

OK, since I’m doing a terrible job explaining with words, here’s pictures of the mock-up.

Here’s what it looks like from Ikea. I’m out of shelf space, but have big voids above the CDs were I could stack more.


So I’m building these out of 6mm baltic birch ply, but I need to join them in some way more permanent than blue tape.


With the result being that I can double stack them in the shelving unit like this.


I’m not wild about the idea of having to put small pieces of wood in the corners. The plywood legs already cost me 2 CDs per shelf of lost space. I don’t want to increase that as even with double-stacking every cell in the unit I still have close to too many CDs.

[Yonak Hawkins]

How about eliminating the side supports and rest the shelf on shelf supports ? ..Recoup the CD space you are losing and no joint to fuss with.

[Ty Williams]

My concern with using shelf pins is that it would be easy to put a CD in a little too far and knock the shelf back off the pins and spill all the CDs to the floor.

[Jamie Buxton]

I like Yonak's suggestion of standard shelf pins. It even recovers those two CD slots your prototype gave up. You don't need to buy a whole shelf-pin jig. You can just make a template to position all the pin holes the same height above the existing shelf.

You do appear to have unused height, so you could make the new shelves a bit thicker to avoid sag.

[Jamie Buxton]

My concern with using shelf pins is that it would be easy to put a CD in a little too far and knock the shelf back off the pins and spill all the CDs to the floor.

Put a downward rim on the front of the shelf to prevent it from doing what you describe.

[Phil Thien]

Put a downward rim on the front of the shelf to prevent it from doing what you describe.

Or notch the bottom of the shelf at each shelf pin location, which would also lock the shelf in place.

[Yonak Hawkins]

... you could make the new shelves a bit thicker to avoid sag.

..Plus it would make the look more coherent. The existing members are solid-looking and the thin shelf tends to look rather spindly.

[Jamie Buxton]

One been-there-done-that tip...

The existing walls look to be too thin to handle two back-to-back shelf-pin holes. If you build a careful template which makes all of the holes some given distance from the front of the wall, the back-to-back holes will collide, and you won't be able to fully insert two pins. The fix is simple. Set up your template so that the pins on the left of a shelf are at different distance from the front than the pins on the right.

[Ty Williams]

I was seriously considering the shelf pins when I realized they won't work. The outside "walls" of the structure are a hollow torsion box construction. There's nothing to stick a pin into.

[Yonak Hawkins]

While there are solutions, even considering the hollow shelving, if you're set on supporting the shelf with side struts, I believe a 1/4" wide glue surface the full length would yield an adequately strong joint, as there are really no significant stresses on it.

[Ty Williams]

Well, I had wanted to use 6mm ply for everything to keep the volume taken up by the shelf to a minimum, both here and WoodTalk there were people concerned about sagging of the 6mm ply over time even with very little weight on it. I decided to switch to 12mm ply for the top/shelf portion and keep everything else 6mm. This solves the joinery question as well, since I could rout a 6mm thick by 8mm tall rabbet into the edges of the top, giving CONSIDERABLY more gluing surface. Moving to 12mm for the top/shelf also gives a much large gluing surface for attaching the stop in the back. I think this is the version I'll be going with.