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3/4 Pine Plywood not flat

1K views 13 replies 7 participants last post by  AlaskaGuy 
#1 · (Edited by Moderator)
Hey guys,

So I made my first work bench awhile back. The top is two pieces of 3/4 ply glued together. The ply is probably from Asia. Sticker said pine and each piece has 11 ply's and no voids. A year later I'm checking the table for square and it has a belly straight across the center. The top is 2 ft x 4 ft on a frame that is 18" x 48". The frame is square and level. I took the top off and middle is still sunk.

I'm wondering if this is because the ply is poor quality? I can't figure it out. Any help is much appreciated. Thanks
 
#5 ·
Everything's pretty damn close to level and square. I've never had anything incredibly heavy on top of it either that I can think of. I put some screws through the top down into the frame, that helped a bit but there's still a bit of a valley.
 
#8 ·
I honestly wouldn t trust Asian plywood for anything that needs to remain straight. I ve bought several sheets from the Borg, and the sheets I found that weren t warped when I bought them would warp after a few months. Your best bet would be to use a good MDF-core plywood. It costs more, but will stay straight.

- lumbering_on
MDF is your friend in this case. BUT don't forget the edges of MDF are poor for wear. You will need to attach a skirt of wood around it to strengthen the edges. This is a small version of this idea. You can finish it anyway you like. For a benchtop I use Formica. Tough stuff for most applications and glue doesn't stick to it so you don't glue something to your table.

Wood Rectangle Wood stain Hardwood Varnish
 

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#9 ·
MDF is your friend in this case. BUT don t forget the edges of MDF are poor for wear. You will need to attach a skirt of wood around it to strengthen the edges. This is a small version of this idea. You can finish it anyway you like. For a benchtop I use Formica. Tough stuff for most applications and glue doesn t stick to it so you don t glue something to your table.

- woodbutcherbynight
This. I would do double or triple MDF top, with a 1/8" piece of sacrificial hardboard. Wrap around the edges with something durable like maple, ash, oak, etc. When the hardboard gets too beat up, pull it out and flip it over. Then replace when that side's done. I did that with my garage workbench and my assembly table.
 
#13 ·
How do you guys go about securing two pieces of mdf to each other? How does mdf react to humidity? I know it s super flat. When you wrap hardwood how do you guys attach it to the top?

- Pyro
Pre drill screws like sheetrock. Countersink the mating surfaces slightly. Apply glue and screw it down, clamp, let dry. To deal with edges I use biscuits and glue.
 
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