Sliding dovetails with plywood

[todd1814]

I had planned to do this with a project but recently read that plywood won't be strong enough. Has anyone tried this? What part of the joint won't be strong enough?

I'm building a small cabinet with a shelf that will have about 40-50 lbs of weight on it. Because of the design, I can't have any fasteners coming in from the outside. I don't want to have plugged holes either. Initially I planned to use dado's to hold the shelf. I later decided that sliding dovetails would help hold the sides together too. The top of the cabinet is a hinged lid so it won't provide any support in holding the top together. The front and back of the cabinet will have a face frame so the back can't provide lateral stability either.

I'm using 3/4" Red Oak Plywood but who knows what the center is made of. I haven't counted the ply's (if that makes a difference).

Any advice is appreciated!

[Bob Bowles]

[Igor]

Dowels?

[Peter Ashby]

You can cut the joint, though if you are using a router on the ends of the shelf scribe the veneer prior to crosscutting with the DT cutter to prevent breakout. As for stability, one shelf will help but on its own I agree with the other posters. Peter

[Bigpole]

Biscuits

[Dan Dresner]

Seems to me that if you dovetail a long pin on the edge of a sheet of plywood, you are effectively reducing the support of the joint to a tenon the thickness of the base of the pin. The plies that form the top and bottom of the pin will have been separated from the rest of the sheet and would now be held to the sheet only through the glue that bonds the plies themselves. If you mentally exaggerate the movement of the joint under racking and deflection stress, you can visualize that the stress on the "orphaned" plies will only weaken their bond to one another: any support from the wider portions of the pin would contribute to the strength of the joint only as long as the fibers and glue in them remained microscopically intact.

Furthermore, if you imagine that the wider portions of the pin have become completely separated, the joint now actually consists of a flat-sided tenon housed in a long "tail", supported only by the inner, narrow edge of the tail.

I'm an amateur hobbyist, so I sure can't claim any certainty, but it seems to me that the strongest joint would be a good old dado, which would maximize the glued surface area, minimize any compromise of the plies, and give the most wood-to-wood anti-racking contact.

It sounds as if you are making a stereo cabinet: how about adding hardwood cleats under the shelves and/or corner braces at the back of the cabinet?

DanD

[Renata]

Slightly different scenario:

I was going to do this very thing (dovetails w/plywood) but for a different purpose. I'm trying to suspend a shelf within a cabinet (say for a VCR) and was planning on using dovetails to act in concert with the glue to hold the shelf in place (suspended). i.s. sliding (pins?) dovetails on the underside of the shelf above, who's counterparts (tails?) would be the side pieces of the suspended shelf. That way you have a bit of a structural joint just in case...

Ya suppose this might not be a good idea? Alternatives? Alternatives that don't involved hardware? Or, is there hardware I can hide (kinda like a bed rail doohickey)?

Thanx Renata

[Peter Ashby]

The same criticism can be made of a solid wood sliding dovetail in straight grained wood. Since modern glues are reputed to be stronger than the wood.....

Strength is not the issue, stiffness is. Without fasteners there is only the glue holding the sides together. The OP does not want fasteners yet wishes some stiffness, a sliding DT joint is thus the joint of choice. Debate is then over exactly how much stiffness one such joint at either end will impart. The choice of joint is correct.

Peter

[Peter Ashby]

I think I see what you mean. If you want to do this without hardware then your choice of joint is correct. If your stock is thick enough and the pin angle is right it should also be strong enough.

Peter

[Renata]

OK - thanx.

3/4" thick but I'm not sure of the angle that the router bit has. Would closer to vertical (angle) be better?

Thanx Renata