Workbench Top - Attach 1" Oak to plywood - Glue & Screw?

[Doug Hobkirk]

I am making a workbench for a shared workshop for a non-profit that recycles household goods on a big scale - the building is about 7,000 square feet, the workshop is about 25x30. We repair donated furniture, salvaging parts out of furniture that cannot be saved.

I am building the bench out of wood we have on hand.

I built the carcass out of 3/4" plywood with some extra bracing - it's rock solid.
The 30x60 top is 2 layers of 3/4" plywood glued and screwed, with a longitudinal and 2 cross braces made of some magnificent plywood (1" thick, 5 or 5" wide, about 14 plies - I didn't see what piece of furniture they came from, but maybe fancy bunk beds).
I added a 20" wide clamp on the end (1" proud, allowing for the top layer described below)
The edge will be faced with 3/4" maple, 2 1/2 wide, matching the top thickness

I want to use 1" of solid oak for the top that I made from left-over table extensions.

I have planed the oak (I have a DeWalt planer in my home shop).
The oak is not continuous strips - I have two 11" wide pieces (40" and 32"), three 9" wide pieces (38", 11", and 11"), and two 10" wide pieces (42" and 30").
Everything is cut square and it all fits together properly.
I plan to layout the wood so the joints are staggered as best possible (I cut the 9" wide boards [They will be in the center] into 3 pieces rather than two at 42" and 30" to improve the stagger effect)


How should I attach the oak to the top? I have access to both sides of the plywood substrate (the beamed top can be lifted off the base carcass).

Glue each piece to the plywood and them screw it from the bottom, screws every 5 or 6inches?
Just screw it to allow for seasonal change? The shop is inside, the building temperature is at least 60 in the winter and never above 75 in the summer.
I plan to put biscuits every 9-10" - or is that a waste of time?
I do have a Kreg setup, so I can also join that way also.
I plan on sanding the top to about 120 and finishing with oil.

Thanks!

PS - A shared workshop (about 10 regular users and 6-8 occasional users, as many as four simultaneously) is quite a different experience than my personal workshop!

[Peter Quinn]

I'd run battens across the bottom of the oak top, across the grain, with elongated screw holes to allow movement. Probably every 12" or so. This will allow air both above and below the top. Solid wood tops do not like to be sandwiched on top of plywood with limited air movement, it can cause cupping. The battens need not be any thicker than perhaps 1/2", though I suppose they could be I'd secure the entire top to the cabinet with a few screws so it is solid but can move.

[Todd Burch]

Those oak pieces are not going to pull 2 thicknesses of glued and screwed 3/4" plywood out of flat. Put it together however it is easiest for you.

Todd

[John A langley]

Doug. That's an interesting method that you came up with for a workshop bench. It sounds like it is out of necessity. I'm going to take a guess. Try some dabs of silicone staggered along the wide boards about every 6" apart. It might still allow the oak to move whereas the plywood is pretty stable. You can weigh the oak down or clamp it overnight. This is how we apply our MDF build up on our solid surface countertops. Some other minds may come up with something better. Good luck.

[Bill White]

Yu didn't say anything about bench dogs. If that's not an issue, glue away. I don't think that screws will be a major asset, but that's just me. Titebond II 'cause there's not a lot of flexing in that glue.
Bill

[ian maybury]

It's not really a fix, but if the oak is not bonded to the plywood (and edge face to edge face) then there may be a risk of some odd bouncing and springing effects when hammering down on it - especially if it cups a bit. Plus it's going to function as a sort of separate layer rather than being structurally a part of the top that contributes as much to its stiffness as it could.

It sounds like you have done it, but gluing the two layers of plywood together will significantly add to the stiffness for the same reason.

Against that if you glue the oak down fully to gain the full structural benefit there's the risk of splitting and all the various problems that could be caused by the different rates of movement of it and the ply.

Don't underestimate the amount of movement that's possible, it's not untypical to separate factory made (and presumably well dried) solid oak flooring boards of maybe 75mm width by about 1mm using washers while putting them down - and they take up those gaps no problem as they equilibriate to the room.

This might sound like a cop out, but might it be best to keep the oak for something else, and to glue and screw another layer of ply to the top instead?

[Howard Acheson]

The first point to make is that it's not a good idea to glue or otherwise firmly laminate a solid wood over a composite material like plywood. The solid wood will want to expand and contract with changes in relative humidity while the composite material will have little appreciable change. If's it's not free to expand/contract it will cause the tabletop assembly to warp or otherwise split or fail. Oak is one of the least stable woods having large changes across the grain. For example, the solid 30" white oak surface will expand/contract 1/4" to 1/2" with a seasonal change is relative humidity.

Why do you want put the oak on top? Have you considered instead adding a 3/4" MDF on top of the plywood? You could then add a covering of 1/4" hardboard (masonite) the could be attached so it could be replaced if it gets too banged up. This would give you a heavy, solid bench top that should last years.

[Jim Matthews]

If the surface is going to be used heavily, a sacrificial top surface might better serve.
I would suggest hardboard mated to the plywood with carpet tape.

That surface could be finished or waxed to make for an easy to clean bench.