joining plywood panels - Woodworking Talk - Woodworkers Forum
 
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post #1 of 20 Old 12-07-2012, 03:52 PM Thread Starter
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joining plywood panels

Hi. This is my first post. I am making a box or a case of sorts. It's not a fine woodworking project; it is purely functional. It is based on the road cases that touring shows use, like this:

http://www.disco-world.co.uk/images/...Case_Large.jpg

Normally the panels of these cases are held in place with aluminum extrusion and rivets, however I need to inside of the case to be perfectly flat--no rivets or aluminum poking through.

So my question is what is a strong enough method of joining the panels? I was planning on using 3/8" or 1/2" plywood (I want to keep the weight down). The outside edges of the box will be covered with aluminum angle iron. I want to be as efficient as possible in terms of labor and materials, so if I can avoid having to make additional cuts that would be preferable.

Again, this is purely about functionality, so if screws would be adequate, that's fine. The case is going to hold books, so it needs to support a bit of weight.

If you couldn't tell, I'm not very experienced when it comes to working with wood, and I greatly appreciate any help.
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post #2 of 20 Old 12-07-2012, 04:09 PM
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If you don't want to go thicker than ˝" ply, I would use rabbets and glue. You could still use a fastener on the outside, since you have an angle to cover the joint.




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post #3 of 20 Old 12-07-2012, 04:16 PM
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Little more work and $, but glue it up out of 3/8 or 1/2 plywood, then coat inside and outside with fiberglas mat and resin. You can reinforce the corners with a second strip of mat. Hardware can be glassed right in.

Alexis de Tocqueville was a very smart man.
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post #4 of 20 Old 12-08-2012, 06:01 PM
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You could use Chicago screws and slightly countersink the portion to the interior of your box. These will give you a mechanical attachment which wood joinery likely wouldn't be as strong for in the dimension material you're working with.

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post #5 of 20 Old 12-09-2012, 06:39 PM
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Hi, nichoth, I am also in event production. Could you describe the reason why the insides of the cases must not have any fasteners penetrating them?

I would really think about drilling shallow holes in the inside of your panels so you can sink nuts into them, or install pan-head machine screws from the inside if you don't mind having nuts exposed on the outside of the case.

Either of these ideas will be a lot more expensive than rivets or wood joinery, but honestly, you need a solid way to attach corner pieces to your cases. If you don't they probably won't last very long on tour.

Making a strong rabbit joint in 3/8" plywood sounds hard. I'd think you would need to use a hardwood plywood so the tool doesn't tear rather than cut.
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post #6 of 20 Old 12-09-2012, 06:39 PM Thread Starter
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Quote:
Originally Posted by Alchymist View Post
Little more work and $, but glue it up out of 3/8 or 1/2 plywood, then coat inside and outside with fiberglas mat and resin. You can reinforce the corners with a second strip of mat. Hardware can be glassed right in.
Resin is lightweight, but having worked with it before I don't plan on ever using it again because it is so toxic.

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You could use Chicago screws and slightly countersink the portion to the interior of your box. These will give you a mechanical attachment which wood joinery likely wouldn't be as strong for in the dimension material you're working with.
These are pretty cool. I had never heard of them before.
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post #7 of 20 Old 12-09-2012, 08:40 PM
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Some years ago, my son and I built a large amp road case for his band. We used half inch ply with rabbits and glue joints. Aluminum angle and corner reinforcements were installed. It is still in use today. It gets some pretty rough use. I can't remember where I got the hardware. It was a Canadian company. Google Amp Case Build and you will see the similarities to what you are after.

Roger from the Great Horicon Swamp
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post #8 of 20 Old 12-10-2012, 06:10 PM Thread Starter
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Some years ago, my son and I built a large amp road case for his band. We used half inch ply with rabbits and glue joints. Aluminum angle and corner reinforcements were installed. It is still in use today. It gets some pretty rough use. I can't remember where I got the hardware. It was a Canadian company. Google Amp Case Build and you will see the similarities to what you are after.
Good to know that rabbets and glue are strong enough.
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post #9 of 20 Old 12-14-2012, 12:45 PM
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This is the perfect job for pocket hole joinery. I would drill all the pocket holes on the inside surfaces then plug them when done. This would give you a very clean look and it would be very strong.

Kregg makes a jig that can be used in 1/2" stock. I don't know if it will work on 3/8" stock or not. You would need to verify that if you decide to go with 3/8".

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post #10 of 20 Old 12-15-2012, 11:38 AM
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I'll respectfully disagree with you about using pocket joinery on 1/2" plywood. The stress of the screw biting into the adjoining material is going to delaminate the layers of ply. Rabbets or dadoes with plenty of glue would be much better.
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post #11 of 20 Old 12-16-2012, 09:14 AM
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Originally Posted by Homewright View Post
I'll respectfully disagree with you about using pocket joinery on 1/2" plywood. The stress of the screw biting into the adjoining material is going to delaminate the layers of ply. Rabbets or dadoes with plenty of glue would be much better.
You have every right to disagree, but until you actually do, it don't comment on how it wont work. I have used the Kregg jig to build many 1/2" plywood shipping crates and it is very strong. I was answering the OP question and basing it off of personal experiance. I would never recommend a process that I haven't tested and proven myself.

My apologies to the OP for this. I just wanted to give you another option, and clerarify it will work and be plenty strong. I have used the Kregg (black) pocket jig on 1/2" ply many times and it is very strong. I will continue using pocket hole joinery on my shipping crates in the future.

Mike Darr

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post #12 of 20 Old 12-17-2012, 06:47 PM
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We can agree to disagree. I don't see such a joint holding up for the long term unless you're using cabinet grade ply which again would be better with rabbets or dado joinery. Shipping crates for a single usage don't qualify for long term proof.
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post #13 of 20 Old 12-18-2012, 08:17 AM
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Quote:
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We can agree to disagree. I don't see such a joint holding up for the long term unless you're using cabinet grade ply which again would be better with rabbets or dado joinery. Shipping crates for a single usage don't qualify for long term proof.
You just made my point. You said you don't see a joint like that holding up. That says you have never did it. That is not fair to the OP.

I have shipping crates that I have been shipping the same item back and forth across the country for years. In my case shipping crates aren't a one time use. That's why I built them the way I did.

I was giving the OP a cheap alternative based on real world experience. Since he stated he doesn't have much woodworking experience he most likely does't have the tools to cut rabbets. You aren't helping anybody by telling them what you think might happen. That isn't what this forum is about.

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post #14 of 20 Old 12-19-2012, 02:45 PM
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Since you obviously can't accept the agreement to disagree I'll put it quite plainly here. Building crates isn't very far up the evolutionary ladder of woodwork. It's not a rocket science approach to building a box. It's simply you've landed on one method which works for you in a very finite approach. Good for you. But I'd venture to say if he has any tools at all, he'll be able to rabbet or dado before having the specialized jig Kreig makes. I stand behind my statements and quite frankly don't need to have tried something to see where its shortcomings might occur. I've been working with wood over 40 years and know what I know.
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post #15 of 20 Old 12-20-2012, 11:11 AM
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It seems like with plenty of glue both would do the trick.
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post #16 of 20 Old 12-27-2012, 02:08 AM
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+1 for rabbet and dado on plywood. Screw makes damage on plywood layers even if the ply is pre-drilled. Layers will split out eventually. This is my expirence.
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post #17 of 20 Old 12-27-2012, 09:01 AM
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Quote:
Originally Posted by Midwest Millworks View Post

I was giving the OP a cheap alternative based on real world experience.

Mike Darr
My opinion..."cheap alternative" is an understatement.

My opinion... Pocket screws are junk joinery.

My opinion...It's still a butt joint, which is the weakest joint.





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post #18 of 20 Old 12-27-2012, 11:31 AM
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you could also run a 1/8" slot cutting bit along the edges and insert a spline between the pieces. a lot depends on the clamp-ability of you pieces - size.

as a test, i have actually butt joined, with glue only, 1/4 ply and it is holding today (6 yrs) as a cabinet back.
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post #19 of 20 Old 12-28-2012, 01:49 PM Thread Starter
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I made a prototype by rabbeting and gluing 3/8" CDX plywood. The dimensions are 24" x 14" x 12", and it seems to hold up well when filled with books.
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post #20 of 20 Old 01-05-2013, 07:22 PM
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Agreed!
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