Looking for advice on strength of joints

[Michael Lande]

Hey there. I’m new to this forum and a pretty new woodworker. I am building a couple of large “ceiling clouds” to hang in a music mixing room (my “plan” is attached below).

Each “cloud” is a roughly 8’ x 8’ square frame of 4-1/2” wide 3/4” cherry wood - assembled like the walls of a box, not a picture frame - with mitered corners (how hard can they be? haha)

The bottom of each “box” will be made up of three open frames (each assembled from 6/4 poplar and assembled like a painting canvas frame and covered in fabric) and two 7” wide 3/4” cherry boards alternatingly laid into the bottom of the frame - so frame, board, frame, board, frame. All of these will be screwed to each other and to the frame from the inside.

I’ll add an additional cross bar to help prevent any sagging.

Each top corner will have 2’ x 3’ gussets, flush with the top edge and glued/screwed in from the outside. This entire box will be filled with rigid insulation and hung on the ceiling from pad eye plates screwed into the centers of the gussets.

This seems pretty strong to my inexperienced self and I live in California where the weather fluctuations aren’t extreme, but I’m at a loss as to whether these things will hold together over time. Will expansion/contraction be a problem, especially with the mitered corners?


Thanks for any thoughts on this.

Cloud.jpg

[Thomas McCurnin]

They hold no weight other than their own structure, right?

Miter joints aren’t very strong, but you gave gussets on top which should hold everything together. Splines or glue blocks would add considerable strength with no weight.

[Michael Lande]

Thanks, Tom. Yes, the structure itself is the only weight (I'm not sure how much that will be yet). Also, they will not be moved in any way once they are hung.

Glue blocks would be easy for me to add and I'll do that.

Michael

[Jim Becker]

I think your method will be fine for the intended application. These are hung statically and only have to carry their own weight. The corner gussets will do the majority of the work.

I may be doing something similar for a future shop to help control sound...I'm spoiled by an acoustic ceiling presently.

[Charlie Jones]

The wood will move across the width of the boards. It should not be a concern here.

[Michael Lande]

Thank you, Jim and Charlie. Very helpful.

Not having a lot of experience, accounting for wood movement seems like an incomprehensible artform. I was also a little concerned that suspending all the weight from the gussets themselves might be an issue. Glad to hear this should all work fine.

[Alex Zeller]

Normally I would say screwing into the edge of plywood is not a good idea but with glue and not much weight it should work. It's much better for the plywood gusset to be screwed through the face into the boards however the edge of the plywood would be seen from the side. A better idea would be steel corner brackets (or shelf brackets so you have a place to suspend it from) with either short screws on the inside of the miters or countersunk flat head screws on the outside and nuts on the inside.

[Dave Mills]

The only thing that strikes me is the use of 6/4 poplar. Since it's only holding its own weight with a span of just 4ft, I'm not sure of the need. Especially if the 6/4 direction is laying flat if I'm reading right. Seems like overkill. Not that I've ever built such a thing!

[Michael Lande]

Normally I would say screwing into the edge of plywood is not a good idea but with glue and not much weight it should work. It's much better for the plywood gusset to be screwed through the face into the boards however the edge of the plywood would be seen from the side. A better idea would be steel corner brackets (or shelf brackets so you have a place to suspend it from) with either short screws on the inside of the miters or countersunk flat head screws on the outside and nuts on the inside.

Thanks, Alex. I can use steel corner brackets for strength but I was using the gussets also as a way to get the hooks where I need them (inset from the corners so you don't see the hanging wire once installed). I suppose I could glue and screw sections of the 6/4 poplar around the inside of the corners, 3/4" from the top edge, and then glue and screw the gussets through their faces into those poplar pieces. That way the gussets would still be flush with the top edge. Does that seem better than my current plan?

[Michael Lande]

The only thing that strikes me is the use of 6/4 poplar. Since it's only holding its own weight with a span of just 4ft, I'm not sure of the need. Especially if the 6/4 direction is laying flat if I'm reading right. Seems like overkill. Not that I've ever built such a thing!

Thanks, Dave. Yes , the poplar will be laying flat (it will be 8' long). The only reason those panels are there is to hold the fabric in place - like a painting frame for canvas but with acoustic fabric instead of canvas. When the cloud is suspended from the ceiling you will mostly see the fabric, flush with the bottom edge of the main frame, and intersected with the two wood panels (which will hold some flush mount lights). I was thinking I could probably get away with narrower poplar, but figured I'd rather err on making it overbuilt instead of underbuilt. I've never built such a thing either!

[Alex Zeller]

I was thinking something like this. You could attach the wire to the diagonal support. That way no eye bolt is even needed.
51odtkNDraL._AC_SY355_.jpg

[Warren Lake]

Never seen acoustic panels made so large

[Michael Lande]

I was thinking something like this. You could attach the wire to the diagonal support. That way no eye bolt is even needed.
51odtkNDraL._AC_SY355_.jpg

Argh. Won't let me see you picture. Got a message saying "On May 2, 2019 we removed privileges to view pictures…"

[Jim Dwight]

If you have to go to the lumber yard and buy it, cherry is much more expensive than poplar. I think alder is also pretty inexpensive in the west where you are. Where it will show, if you like the look by all means use cherry but for hidden parts, I would use something cheaper. If you want the corner braces to be wood, using solid wood, instead of plywood, would hold screws better. Or you could use plywood corner braces but put holes for pocket screws in the braces and screw them to the outer plywood frame. It's the screw into the edge of the plywood you want to avoid, it tends to just split the layers.

[Michael Lande]

If you have to go to the lumber yard and buy it, cherry is much more expensive than poplar. I think alder is also pretty inexpensive in the west where you are. Where it will show, if you like the look by all means use cherry but for hidden parts, I would use something cheaper. If you want the corner braces to be wood, using solid wood, instead of plywood, would hold screws better. Or you could use plywood corner braces but put holes for pocket screws in the braces and screw them to the outer plywood frame. It's the screw into the edge of the plywood you want to avoid, it tends to just split the layers.

Yes, cherry is expensive! I'm matching some other wood in the room and in my staining test the cherry matched better than alder. All the cherry will be visible so I'm biting the bullet (but using poplar for the hidden parts). I can do glued edges and pocket holes on the plywood gussets, but I'm hanging the entire panels from them. Wondering if they will be strong enough since the panel will be suspended above my head! Same worry about solid wood - seemed like plywood would be stronger. Earlier in the thread I brought up the idea of gluing and screwing (there's got to be a better way to say that) sections of the 6/4 poplar around the inside of the corners, 3/4" from the top edge, and then glue and screw the gussets through their faces into those poplar pieces. Not sure if that's actually weaker, though.