Plywood butt joint with screws strong enough? - Woodworking Talk - Woodworkers Forum

 
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post #1 of 10 Old 02-16-2017, 04:53 PM Thread Starter
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Plywood butt joint with screws strong enough?

Anyone know if joining plywood together at a right angle with screws would be strong enough for a shelf? I'm new to woodworking and already cut and painted my shelves. I'm starting to put them together and I'm worried it's too heavy to be safe. Any suggestions would be greatly appreciated! Here is an image of the shelf: http://imgur.com/a/Rmbpy. Additionally, the thicker boards are just two pieces of 3/4" plywood glued together...

Last edited by jpro1001; 02-16-2017 at 05:04 PM. Reason: Added wood thickness details.
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post #2 of 10 Old 02-16-2017, 05:13 PM
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If the sides didn't show there certainly wouldn't be anything wrong with putting it together with screws. I would also use wood glue. What's shown in the image the sides do show. I think you would be better off using glue and finishing nails instead of the screws.
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post #3 of 10 Old 02-16-2017, 06:19 PM Thread Starter
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The sides won't show, they will be up against a closet wall. I was thinking that since plywood is multiple layers of thin pieces it's not very strong if you screw into the side of it. It seems brittle. This shelf is very heavy and I don't want it to fall on my kids (or anyone). I guess I was hoping for a magical joint solution (without building it all again) or a new type of hidden brace/bracket design I haven't seen before... The wood just doesn't seem very strong. The few screws I tried putting in so far went in like butter...
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post #4 of 10 Old 02-16-2017, 06:19 PM
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I agree with Steve, but I think you should still drill small pilot holes if you hand nail to avoid getting "shiners".

If you don't have time to do it right the first time, when will you have time to do it over?
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post #5 of 10 Old 02-16-2017, 08:47 PM
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Quote:
Originally Posted by jpro1001 View Post
Anyone know if joining plywood together at a right angle with screws would be strong enough for a shelf? I'm new to woodworking and already cut and painted my shelves. I'm starting to put them together and I'm worried it's too heavy to be safe. Any suggestions would be greatly appreciated! Here is an image of the shelf: http://imgur.com/a/Rmbpy. Additionally, the thicker boards are just two pieces of 3/4" plywood glued together...
How are you going to attach the shelves to the wall?
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post #6 of 10 Old 02-16-2017, 09:03 PM
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Originally Posted by MT Stringer View Post
How are you going to attach the shelves to the wall?
You will need to add a hanger strip (1 X 2") under the top shelf to hang this assembly.
And it will best to hit 2 or 3 studs to hang. Otherwise you will be using toggle bolts and on a shelf that big, that will be more difficult.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #7 of 10 Old 02-16-2017, 10:57 PM Thread Starter
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Yeah, I was planning on using 2x2s as a sort of hook at the top possibly on each shelf. The 2x2s will be in the studs and the side panels will also be in studs. So you guys really think plywood is strong enough to hold the butt joins? I didnt put glue on the joints. I guess i can back the scews out and glue them too. I would need to sand the paint off for glue to stick right?
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post #8 of 10 Old 02-17-2017, 09:01 AM
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You should glue. With glue and screws it should be very strong. Be sure you hang it securely.
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post #9 of 10 Old 03-08-2017, 02:49 PM
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Butt joints with screws in endgrain is a very weak joint. I would not feel comfortable with heavy shelves secured this way. Screws in the end of plywood are notorious for pulling out.

A pocket screw would be much stronger than a screw stuck straight into the end, but still not great.

Pockets screws with glue would be better.

Dadoing a slot for the shelves to sit in would be ideal, but looking at your design not sure you could work that in.

I would consider adding some kind of mechanical fastener. This could be small L brackets (you could make a slot for it so it doesn't stick out), or small gluing blocks. With little Gluing blocks you can angle them, then paint the outside edges the same color as the shelves. This would still look nice and add a ton of strength.
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post #10 of 10 Old 03-13-2017, 11:46 AM
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I've had bad luck with screws going into the edge of plywood.

I've done something similar, but making the joints rabbet joints at the edges and dados for the shelves, and that held up quite well. Another thing I've seen suggested, but haven't tried, is drilling an oversized hole in the edge of the plywood, gluing in a solid wood plug, and then driving the screws into that. I'm not sure how it works, but it sounds like it might take care of some of the issues.
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