plywood – screws or nails when anchoring into Edge or End grain
digitallimit
| Posted in General Discussion on
Need your folks experience and recommendations.
When connecting plywood together and anchoring into Edge or End grain… is it better to use nails or screws or even dowel?
I am using simple box joints for a project, but not sure what constructive method to use.
Replies
Hey there,
Maybe you could tell us a little bit about your project and we can better help to give you some advice!
Hi Eideann,
I want to make a simple wooden version of a craftsman tool chest. I do not have a lot of power tools yet like:router, tablesaw, biscuit joiner, so it will be limited on tool capability.
thank you
Screws and glue will hold a plywood box together very well. Nails would not hold together as well in the edges of plywood.
Box joint is another term for finger joint. If that is really what you are doing, then you don't need any fasteners other that glue; assuming all of the fingers fit well.
If you are using plain butt joints, then just glue and clamp. If you want a little more strength, add some triangular glue blocks on the inside of the corner. Or, you could add some dowels after it is glued up.
I hate to be finicky, but finger joints are thinner than box joints.
Anyhow, edge joints hold up well with just glue. If you're going to use screws, use coarse-threaded. They grab the plies better. And you can use dowels if you're industrious. But like Eideann said, we can only guess without a better idea.
Good luck,
Mikaol
Hey there,
Like suggested, screws are the better option in plys. What tools do you have? If you have a circ saw and a drill you can really made a fair amount of things to get yourself going. There's nothing wrong at all with screwing some plywood together when you're starting out. You could look into getting a pocket hole jig if you want to hide the screws. They get a bad rap, but they're perfectly serviceable for tasks that they're meant for - as in they're not meant to be a replacement for a dovetail or mortise and tenon. For case construction and face frames they're great.
I made a big mistake. I still get the type of joints mixed - I am using a 'plain butt joint' as Bilyo pointed out. I apologize for the confusing.
How would I keep the screws from separating the plies and bulge the top layer?
Predrilling pilot holes will help with that. Use a drill bit that is a bit smaller than your screws to get started, then you can drive the screws in with minimal bulging.
@Eideann
Would I predrill the full length of the screw or just half the length as a starter?
You don't necessarily have to drill out the entire length of the screw. I usually like to leave a bit of wood for the screw to bite into. You can try a couple test pieces to see what's working well for you. You can want to use a small a bit as possible to mitigate potential bulging and splitting while leaving enough room for the threads to really bite down. Big Box store plywoods are notorious for being inconsistent and sketchy on their inner plys.
Putting screws into the edge of plywood is always risky. Even with pre-drilling, there is a good chance the plys will separate. If you glue your butt joint together first, it will help prevent separation as the cured joint will help hold the plies together. Then, pre-drill and insert your screws. A trick I sometimes use if I think there might be a problem with splitting or ply separation is to put blocks on either side of the edge with clamping pressure before inserting the screw. This doesn't always work as, sometimes, I just can't get a clamp to reach the spot.
I think the easiest and best way to make a butt joint, especially with plywood, is to glue the joint together, let it dry, then drill and insert dowels. Cut them off, sand them flush, and you have a reinforced joint with no worries about splitting the plies. Of course, you have to like the idea of having the exposed dowel ends. They can be spaced in a decorative way, however.
Somewhat depends on the screw type. But in plywood, drill the hole full length with a tapered countersink bit, or else you risk splitting the ply as the screw is driven. That said, if the screws are the self drilling type, depth may be be not as critical, but I suggest drilling full length anyway.
Within 2" of the end of the panel, it helps to place a clamp over the drill site and remove after the screw is driven. This will prevent splitting on the vulnerable edge.
I build a lot of ply cab boxes. My procedure is to align the panels, fix in place with 15ga nails, and place screws about every 6" along the length, 1 1/2" from top and bottom. Most of the time I do not use glue. I don't think there is much benefit in plywood and adds little to no strength. I use 2" screws in 3/4 ply.
What about driving in the dowel below the surface and using a plug over that with the grain going in the same direction? Newbie, don’t shoot!
Screws will work but there's always the risk of splitting, especially if the plywood has voids and other poor internal construction. The screw heads will show and (depending on the screws used) can look a bit ugly. But does that matter to the OP? If the piece is purely utilitarian, perhaps not. If it's furniture, it might matter.
Dowels would be a good jointing method of edge to end of face in a plywood box structure. Dominos or biscuits would also work ... but need a more expensive machine to make the joints. Precise fit and good glue will make a strong joint.
Dowel ends will show on the plywood face whilst biscuits or dominos won't, so plugging over dowels with plugs matched to the grain of the plywood face could hide the dowels, as user-6779032 suggests.
Plugging over the tops of the dowel ends where they would otherwise show means pushing the dowel some distance through the face of the plywood to make room for the plug. If the plywood is thick, there's still be plenty dowel in the face piece being held in place by the glue applied to it. But if the plywood is thin, pushing the dowel through to make room for a plug on top might leave very little dowel glued into the face piece of plywood. That would make the plywood face-to-edge dowelled joint weaker.
Lataxe
Another thought occurred - a lock mitre cutter in a router table can make some very good corner joints in plywood casework. If done carefully and with high quality plywood having a good face veneer, it can look like solid wood.
The lock mitre cutter has the reputation of being difficult to set up well. In practice it's not that difficult if test cuts are made in scrap. For plywood of a given thickness, set-up pieces can be made for putting the lock mitre cutter to the right setting in the router table & fence for later cuts in the identical kind of plywood.
I once made a large plan-chest for a graphic artist friend using high quality 18mm plywood with a very nice maple veneer face side. The veneer had been sliced off the side of a large log to make sections (flitches?) that look like planks of wood, rather than the rotary cut veneer, which is easily identifiable as such.
This plan chest has been to New Zealand and back (from the UK) twice and suffered a few blows in the shipment processes but hasn't given anywhere in it's lock-mitred framework. Strong joint, invisible and no fasteners except the glue.
Lataxe
Last time I made a plywood tool box, I put a section of 2x2 or something like that into each corner and screwed both panels into the 2x2.
I’m a big fan of rabbeting and gluing one edge and then screwing/doweling for this type of construction.
The rabbets and glue will hold together welL enough for the rest of the process to work, and they’ll reduce the amount of visible edge grain.
If the look is not a problem, I drill appropriate pilot holes (correct diameter and a bit longer than the screw) and use screws and glue for some shop fixtures. These have held up to quite a bit of abuse for many years.
The idea of a corner brace inside occurred to me too. Alternatively do the same with an L shaped reinforcement on the outside of each corner. Wrap 1x2 pine or whatever you have around each box corner, glue it all on and you need the screws less.
This would dress up the outside and hide the pLywood edges. You could use a block plane or similar to chamfer the outside corner and make it look nicer.
Mike
Be cautious with power drills, because they can sometimes drill too hard and sink the head in too deep denting the plywood. Variable speed power drills using lower power to ease the screw into place will help. Brace and bit hand drills or a good egg beater style drill are another way not only to pre-drill, but some brace and bit drills can also drive screws.
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