Making a good joint

[Aaron Coffee]

Would the previous suggestions work for 1/2 ply as well?

[kennyrayandersen]

I LOVE POCKET SCREWS...however, never used 'em for a butt joint to extend ply...if I did, I would want to put them in from both directions...one side/one way on one sheet and the opposite side/direction on the other piece with a screw placed at about 2"s apart(staggered from side to side) and I would probably want to use some thickened epoxy as well.........
madjack

It’s a problem generally screwing into end grain of plywood. The screws put pressure that tries to separate the different layers and it will split (inter-laminar tension failure) – it’s the weakest direction for strength in plywood.

[Steve_Cox]

I LOVE POCKET SCREWS...however, never used 'em for a butt joint to extend ply...if I did, I would want to put them in from both directions...one side/one way on one sheet and the opposite side/direction on the other piece with a screw placed at about 2"s apart(staggered from side to side) and I would probably want to use some thickened epoxy as well.........
madjack

It’s a problem generally screwing into end grain of plywood. The screws put pressure that tries to separate the different layers and it will split (inter-laminar tension failure) – it’s the weakest direction for strength in plywood.

I would suspect that the thickened epoxy was to negate the potential damage done by the Interfiber/interlaminar failure due to the multi-axial states of stress. In other words, if you use the epoxy you can just screw it.

[kennyrayandersen]

I LOVE POCKET SCREWS...however, never used 'em for a butt joint to extend ply...if I did, I would want to put them in from both directions...one side/one way on one sheet and the opposite side/direction on the other piece with a screw placed at about 2"s apart(staggered from side to side) and I would probably want to use some thickened epoxy as well.........
madjack

It’s a problem generally screwing into end grain of plywood. The screws put pressure that tries to separate the different layers and it will split (inter-laminar tension failure) – it’s the weakest direction for strength in plywood.

I would suspect that the thickened epoxy was to negate the potential damage done by the Interfiber/interlaminar failure due to the multi-axial states of stress. In other words, if you use the epoxy you can just screw it.

In any composite matrix there are fibers, which is where the strength comes from and a matrix that holds it all together. It seems odd but the epoxy is generally the weak link. However, in wood, the fibers aren't as strong as the epoxy. If the plywood was made from epoxy and wood it probably wood be stable enough to screw into the edge. But I've had both plywood and especially mdf (both) split when screwing into the end grain (edge) of the plywood. Even regular would doesn't hold together as well when screwing into the endgrain. If you pre-drill the plywod it would certainly be less prone to split, or if you glued a strip to the edge that would also work. The epoxy, unfortunately, doesn't setup before the end grain will split. (I think it is probably the wood that actually splits anyway FWIW.

[Steve_Cox]

I LOVE POCKET SCREWS...however, never used 'em for a butt joint to extend ply...if I did, I would want to put them in from both directions...one side/one way on one sheet and the opposite side/direction on the other piece with a screw placed at about 2"s apart(staggered from side to side) and I would probably want to use some thickened epoxy as well.........
madjack

It’s a problem generally screwing into end grain of plywood. The screws put pressure that tries to separate the different layers and it will split (inter-laminar tension failure) – it’s the weakest direction for strength in plywood.

I would suspect that the thickened epoxy was to negate the potential damage done by the Interfiber/interlaminar failure due to the multi-axial states of stress. In other words, if you use the epoxy you can just screw it.

In any composite matrix there are fibers, which is where the strength comes from and a matrix that holds it all together. It seems odd but the epoxy is generally the weak link. However, in wood, the fibers aren't as strong as the epoxy. If the plywood was made from epoxy and wood it probably wood be stable enough to screw into the edge. But I've had both plywood and especially mdf (both) split when screwing into the end grain (edge) of the plywood. Even regular would doesn't hold together as well when screwing into the endgrain. If you pre-drill the plywod it would certainly be less prone to split, or if you glued a strip to the edge that would also work. The epoxy, unfortunately, doesn't setup before the end grain will split. (I think it is probably the wood that actually splits anyway FWIW.

Think of the pocket screw as joint stabilization while the thickened epoxy has time to penetrate and cure in the joint. Of course pocket screws by nature are set in pilot holes and drill their own hole in the substrata being joined. Limiting the torque applied to the screw will determine whether laminate damage will occur or not.

[Forrest747]

Yellowstone was great. Sad to say I did not see any TD in the RV campground we stayed at. We stayed in a cabin hopefully for teh last time. Yet the road calls again and tomorrow its Vegas.

Yet for teh day I have to work on Charley I made up the joint. a simple butt joint with Gorilla glue and a backing plate. Left the gap in the middle to accomodate the loft frame.
I hope it holds.

[Marck]

I've done this on 4 tears

Braggart lol