How to join plywood at 90 degrees without face frame

[Frank Kalder]

I'm trying to build a simple box with veneered plywood for all 4 sides. All 4 sides will be visible, and I can't have a face frame of any sort.

Any ideas on how to join the ply? I want the horizontal top to seamlessly join the vertical sides. If I were making this from solid wood, I'd probably just cut the top and sides at 45 degrees and biscuit them together. I don't think that would work with plywood -- I'd have to get the 45's exactly right for the 1/16 ply veneer to match up. These are fairly big pieces of plywood, and I don't think I could cut 45's that accurately on them.

Any suggestions?

[Myles Moran]

45 degree miter lock bit with a router? As long as you're careful aligning your edge guide you should be able to get fairly close, and then burnishing with a round screwdriver after the glue up should help you hide any imperfections.

[Bill Dufour]

glue blocks?

[Terry Therneau]

Rockler sells a "miter fold" dado set. Essentially, you don't cut the plywood veneer, removing wood up to that point. It's much like the trick of setting 4 cut sides on a long strip of tape and the rolling it up into a box, with the veneer as the tape.
I've never used it, just seen the ads.

[Bill Dufour]

Rockler sells a "miter fold" dado set. Essentially, you don't cut the plywood veneer, removing wood up to that point. It's much like the trick of setting 4 cut sides on a long strip of tape and the rolling it up into a box, with the veneer as the tape.
I've never used it, just seen the ads.

I think that is how Tesla made their pickup truck, origami.
Bil lD

[Bruce King]

If you have straight plywood you can rabbet edges with a thin veneer left. Then the other piece for that corner just fits right in the rabbet. If more strength is needed add some pocket holes before it’s glued up then put in the pocket hole screws after the glue has dried. If you can maintain alignment perfectly the screws can be put in before the glue has set. Having the edge of the thin veneer visible is better than a non perfect miter.

[Brian Behrens]

It seems to me that your issue is not being able to cut accurate 45s on these large pieces. You can make accurate 45s using a chamfer bit on the router table. Do you have a track saw? Or use a circular saw with a home made track. I'm not understanding why you cannot make the cut accurately this way. Check your blade with a combination square and make the cuts, if they are off it is easy to tweak with a handplane. Then use either biscuits as you stated, or splines to reinforce the joint.

[Curt Harms]

I used 3/4" ply for a microwave cabinet and cut 45* miters on the table saw to join the edges. I cut biscuit slots in the mitered edges and glued them up. Once dry I moistened the very edges of the mitered pieces and rolled them together with the shaft of a large screwdriver. I wasn't sure if rolling them together would work but it's stayed good for probably 15 years, YMMV I guess.

[Tom Bender]

Unless you require a lot of strength just glue the miters and forget the biscuits, splines, dowels etc.

[Evan Van Dyke]

Why not use a mitered rabbit joint? Should be even stronger with plywood since you won’t get all end grain in the rabbit.

[glenn bradley]

If you are not setup to process large sheet goods you have set yourself quite a challenge. For sound reinforcement cabinets back in the day, 13 ply marine ply and lock-miter joints were the rule. A lot of sheet goods do not do butt joints (including miters) very well without help; splines, lock miter, biscuits. You do not say what the requirement is for the edges that will show at the 'face'. Can you give us a drawing or a picture of something similar?

Mid Century Modern made use of long miters on veneered ply. Many 'clean' or minimalist designs today do as well. Biscuits can help with alignment. A lock miter or splines can help with strength. I guess I need a better idea of what you are trying to build beyond the one joinery question in order to be more helpful(?).

[Doug Garson]

You could try this approach. https://www.youtube.com/watch?v=dQk_glgNAQk

[Mike Henderson]

I didn't do these corners to hide the joints but perhaps you could do something similar. Go ahead and join your plywood at 45 degrees with splines or biscuits or whatever. Then cut the corners - I think I did this on my router table - and lay in a contrasting wood. That will keep you from having to match the plywood perfectly.

Mike

Box152.jpg

[Ben Helmich]

There’s a YouTube channel called 3x3 Tamar. She showed several different ways to do this using solid wood edging on the ply. You might check it out.

[Doug Garson]

There’s a YouTube channel called 3x3 Tamar. She showed several different ways to do this using solid wood edging on the ply. You might check it out.

Great minds think alike, that's who I linked to.