How to cut a pull out slat bed from a single piece of plywood?

Question

I know the simple answer is to cut the slats separately and making an assembly, I've done that before. This time I want to cut it from a single piece of 3/4 plywood. It will be approx. 3.5ft x 4ft when collapsed and approx. 6ft x 4ft extended with fingers/grooves about 1" in width... I want the slats skinny as it will also serve as a table.

I don't think a jig saw is the right tool; certainly not freehand.

I've considered making one side (forstner bits/table saw) and using that as a router template... but that seems like it would have to be very exact and a lot of wood waste.

I've also considered buying/using a dado blade set, but getting the step/spacing right seems problematic to me.

Or possibly contracting it out to have laser cut... not sure if that would be cost effective, or even possible at that thickness.

Anyone experienced with cutting something like this?

EDIT:

I think I have a good idea of how to do this with a plunge router and 1" bit.

I'll cut the first slot using a fence attachment. And then I'll mount a 1" hardwood follower to the base... (I'm ok with drilling a couple holes in it).

Because the follower is effectively only a half fence I'll probably need to do a plunge entry for subsequent slots, and then rotate/switch directions for the exit. I could probably use the completed half as a template, or just repeat the process. I guess I could rout both halves as a single unit and then cut it in half/assemble/trim.

It will definitely be time consuming and wasteful, but I think it should work; and I can make the assembly for the cost of a sheet of plywood + a 1" router bit.

Any opinions?

FWIW, I have a 2.25HP Triton plunge router kit I can use for this.

Answer 1

To make something like this from a single piece of ply I think the only reasonable way is by laser. This literally looked like a laser path when I first saw the image of your proposed design. Every other method I can think of, including CNC¹, would create 'kerfs' wide enough that this would be hopelessly loose and floppy — 1/8" gaps?

In terms of how practical getting it laser cut is as discussed in the Comments, availability of a suitable laser locally and then the cost are potential issues. Obviously this is ruled out in some locations where there's no laser (or none that you can find), and in others the cost could be prohibitive. Is the design worth persevering with if the table ends up costing hundreds? I wouldn't have thought so when there are other ways of working around what you want to achieve here.

Not using just one piece
Now re. your edit and the idea of using a router with a follower, obviously this is one of a few ways you could do it. In essence you're creating a very long finger joint that will just interlock flat, instead of at 90°.

By likening it to finger joints it immediately highlights a potential problem though. Finger joints can often end up being very tight and require the joint to be tapped together using a mallet or a hammer with a protective block, even as short as they are. Take that same degree of tightness and multiply it by approximately 50 and you have an interlocking thing that you either couldn't push together at all, or without damaging the material irretrievably!

So you need to introduce just a smidge of slop. The easiest way to do this would be some light sanding². Again multiply it up and it's quite a bit of sanding..... but at least it's for a one-off.

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¹ Which even if suitable could have the same potential pitfalls as a laser.

² Being careful to maintain square edges. There's a tip for that in this previous Answer.

Answer 2

A plunge saw on a track (aka tracksaw) would be ideal for the long straight lines. Finish the corners with a jigsaw.

If the tracksaw is unavailable and you're very comfortable with a regular circular saw, you could do it with plunge cuts. Plunge cuts have the potential to be very unsafe (exposed blade, unstable saw, kickback, etc), so please proceed cautiously. You could set up a guide that would help you stay extra straight when cutting.

All this plunge stuff assumes you want to make both pieces out of one ~4x4 piece of ply. If the saw kerf (width of the blade) is an issue, you could subtly taper the fingers so they'd nest more tightly.