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3/4 Pine Plywood not flat

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Forum topic by Pyro posted 12-09-2018 10:07 PM 485 views 0 times favorited 13 replies Add to Favorites Watch
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Pyro

61 posts in 616 days


12-09-2018 10:07 PM

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


13 replies so far

View MikeDilday's profile

MikeDilday

258 posts in 914 days


#1 posted 12-09-2018 10:45 PM

Is the top supported in the middle?

-- Michael Dilday, Suffolk, Va.

View Pyro's profile

Pyro

61 posts in 616 days


#2 posted 12-09-2018 10:49 PM

Yessir. Checked it yesterday, looks good.

View bgilb's profile

bgilb

101 posts in 3513 days


#3 posted 12-10-2018 01:21 AM

Are the 2×4s square?

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Pyro

61 posts in 616 days


#4 posted 12-10-2018 01:32 AM

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.

View lumbering_on's profile

lumbering_on

578 posts in 945 days


#5 posted 12-10-2018 01:33 AM

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.

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Pyro

61 posts in 616 days


#6 posted 12-10-2018 01:37 AM



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.

- lumbering_on

Wow really?

View woodbutcherbynight's profile

woodbutcherbynight

5967 posts in 2864 days


#7 posted 12-10-2018 01:45 AM



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.

-- Live to tell the stories, they sound better that way.

View jmartel's profile

jmartel

8525 posts in 2605 days


#8 posted 12-10-2018 01:49 AM



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.

-- The quality of one's woodworking is directly related to the amount of flannel worn.

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lumbering_on

578 posts in 945 days


#9 posted 12-10-2018 02:15 AM


Wow really?

- Pyro

Unfortunately, where the RH where I live can be anything from 100% to less than 30%, which causes cheap plywood to warp.

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Pyro

61 posts in 616 days


#10 posted 12-10-2018 02:18 AM



Unfortunately, where the RH where I live can be anything from 100% to less than 30%, which causes cheap plywood to warp.

- lumbering_on

Yeah that makes sense, definitely could have happened to me.

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Pyro

61 posts in 616 days


#11 posted 12-10-2018 02:21 AM

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?

View woodbutcherbynight's profile

woodbutcherbynight

5967 posts in 2864 days


#12 posted 12-10-2018 03:08 AM



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.

-- Live to tell the stories, they sound better that way.

View AlaskaGuy's profile

AlaskaGuy

5332 posts in 2764 days


#13 posted 12-10-2018 03:09 AM

Can you post a photo of what you have supporting your 2 layer plywood bench top?

-- Alaskan's for Global warming!

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