# Fixing bowed plywood



## William H (Jun 22, 2020)

I am working on a 16" x 30" drill press table top. I noticed there is a bow of about 1/8 inch in the 3/4" plywood top toward one end. I am hoping to reduce or eliminate this bow without having to remake the whole top. I am usually not able to spend much time in my workshop each week and I have been working on this project for over a month. I am pretty good at selecting wood from the big box store, so I can't believe I would have missed this.

I am using aluminum channel bars on edge which I have clamped to the top. Will this take out the bow?? How long would I need to leave it clamped?? Is there a better way?

Any advice would be appreciated. Thank you.


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## David Nickell (Jul 6, 2020)

There are many others here who can have way more experience to draw from, but I'm going to respond in hopes of getting a conversation going.

When I built my work bench I had a 3/4 inch piece of plywood on hand that had about the same amount of bow in it. I purchased another piece of 3/4 inch piece that seemed straight and without significant flaws. All plywood will have some bow to it. I turned the pieces so the would correct each other and covered them in glue, then set weights all over the plywood until the glue could dry. That gave me a surprisingly flat surface 1 1/2 inches thick for the bench top. It has remained flat, and level, and is solid. 

I don't know if this would be an option for your situation, but it worked for mine. Planing plywood isn't an option, but creating opposing forces held together with glue helps. I also screwed the top to the bench frame without glue so that it can be changed out if ever necessary. The screw heads are recessed so they don't interfere with anything I'm doing on the surface. I would think the weight of a drill press should help hold everything in place if you can start with it flat.


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## woodnthings (Jan 24, 2009)

William H said:


> I am working on a 16" x 30" drill press table top. I noticed there is a bow of about 1/8 inch in the 3/4" plywood top toward one end. I am hoping to reduce or eliminate this bow without having to remake the whole top. I am usually not able to spend much time in my workshop each week and I have been working on this project for over a month. I am pretty good at selecting wood from the big box store, so I can't believe I would have missed this.
> 
> I am using aluminum channel bars on edge which I have clamped to the top. Will this take out the bow?? How long would I need to leave it clamped?? Is there a better way?
> 
> Any advice would be appreciated. Thank you.


Other than the method post just above, there is no good/easy way to fix a single warped sheet of plywood. Leaving it out in the rain, or sunshine after damping it, or weights or clamps have all been tried with various successes, but none were completely flat. Steel angles may work on a single sheet, but aluminum doesn't have the needed rigidity in thinner sections. On my drill press table I used 1" x 3"s to completely surround the sides and front as stops to locate it and retain it. Something like that may work on a larger table like yours, I donno?


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## William H (Jun 22, 2020)

David Nickell said:


> There are many others here who can have way more experience to draw from, but I'm going to respond in hopes of getting a conversation going.
> 
> When I built my work bench I had a 3/4 inch piece of plywood on hand that had about the same amount of bow in it. I purchased another piece of 3/4 inch piece that seemed straight and without significant flaws. All plywood will have some bow to it. I turned the pieces so the would correct each other and covered them in glue, then set weights all over the plywood until the glue could dry. That gave me a surprisingly flat surface 1 1/2 inches thick for the bench top. It has remained flat, and level, and is solid.
> 
> I don't know if this would be an option for your situation, but it worked for mine. Planing plywood isn't an option, but creating opposing forces held together with glue helps. I also screwed the top to the bench frame without glue so that it can be changed out if ever necessary. The screw heads are recessed so they don't interfere with anything I'm doing on the surface. I would think the weight of a drill press should help hold everything in place if you can start with it flat.


Thanks for the reply. At this time I don't have the option of gluing another piece on top or below. I should have thought about the possible bow earlier, but I just get wrapped up in all the other aspects of the project like dado placement, the fence and the drawer construction underneath the table so it is high enough to use the table crank. But it's not really any good in the end if the table isn't flat. Live and learn I guess.


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## Rebelwork (Jan 15, 2012)

Do the best you can and make another later. Plywood is excellent for the projects if it's usable. Sometimes I go to MDF or particle board for jigs and fixtures....

I ended up using walnut ply on mine..


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## William H (Jun 22, 2020)

woodnthings said:


> Other than the method post just above, there is no good/easy way to fix a single warped sheet of plywood. Leaving it out in the rain, or sunshine after damping it, or weights or clamps have all been tried with various successes, but none were completely flat. Steel angles may work on a single sheet, but aluminum doesn't have the needed rigidity in thinner sections. On my drill press table I used 1" x 3"s to completely surround the sides and front as stops to locate it and retain it. Something like that may work on a larger table like yours, I donno?


Thanks for your reply. I am thinking of using a steel angle underneath. That might work if I have a way of attaching an angle along the front & rear. Thanks.


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## William H (Jun 22, 2020)

Rebelwork said:


> Do the best you can and make another later. Plywood is excellent for the projects if it's usable. Sometimes I go to MDF or particle board for jigs and fixtures....
> 
> I ended up using walnut ply on mine..
> View attachment 421618


Looks really good. Nice and flat.


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## woodnthings (Jan 24, 2009)

William H said:


> I am working on a 16" x 30" drill press table top. I noticed there is a bow of about 1/8 inch in the 3/4" plywood top toward one end. I am hoping to reduce or eliminate this bow without having to remake the whole top. I am usually not able to spend much time in my workshop each week and I have been working on this project for over a month. I am pretty good at selecting wood from the big box store, so I can't believe I would have missed this.
> I am using aluminum channel bars on edge which I have clamped to the top. Will this take out the bow?? How long would I need to leave it clamped?? Is there a better way?
> Any advice would be appreciated. Thank you.


Without see your exact construction I can't give specific advice on how to fix it. Are there dado slots for T tracks? How is it secured to the rest on the table? Is removing it out of the question? Can steel angles be screwed to the perimeter? Can wood aprons be screwed or glued our the perimeter and if so, how deep can they be? Got any photos?


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## William H (Jun 22, 2020)

woodnthings said:


> Without see your exact construction I can't give specific advice on how to fix it. Are there dado slots for T tracks? How is it secured to the rest on the table? Is removing it out of the question? Can steel angles be screwed to the perimeter? Can wood aprons be screwed or glued our the perimeter and if so, how deep can they be? Got any photos?


The dado slots are for T tracks. They are routed into pieces of melamine (spelling??) which are glued to the plywood base. The melamine makes up a left and right section on the plywood base, with the middle open for a removeable sliding insert. I am thinking of attaching the angles on the perimeter of the plywood base.


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## Steve Neul (Sep 2, 2011)

A warp is caused because the moisture content of the wood is greater on one side than the other. Without knowing your construction it's difficult to say if this would help but you could wet the concave side of the plywood while drying the crown side. You could put like an electric space heater blowing on the crown side to dry it. You just need to be ready to add some structure to it when you do get it flat or it will warp back.


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## William H (Jun 22, 2020)

Steve Neul said:


> A warp is caused because the moisture content of the wood is greater on one side than the other. Without knowing your construction it's difficult to say if this would help but you could wet the concave side of the plywood while drying the crown side. You could put like an electric space heater blowing on the crown side to dry it. You just need to be ready to add some structure to it when you do get it flat or it will warp back.


Thanks for your reply. It is flat now that I have aluminum channel bars clamped on their edges to the top. If I wet the underside (concave side), would that help or am I still most likely going to need steel angle bars attached to the bottom/perimeter?


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## Steve Neul (Sep 2, 2011)

William H said:


> Thanks for your reply. It is flat now that I have aluminum channel bars clamped on their edges to the top. If I wet the underside (concave side), would that help or am I still most likely going to need steel angle bars attached to the bottom/perimeter?


Right now the wood is under pressure and the aluminum is forcing it flat. It wouldn't hurt to wet the underside to lessen the pressure. When that dries it would probably be helpful to seal both sides with some kind of finish to stabilize it.


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## William H (Jun 22, 2020)

Steve Neul said:


> Right now the wood is under pressure and the aluminum is forcing it flat. It wouldn't hurt to wet the underside to lessen the pressure. When that dries it would probably be helpful to seal both sides with some kind of finish to stabilize it.


Thanks, I will do that.


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## David Nickell (Jul 6, 2020)

A third generation carpenter, the best I have ever known, once told me that anybody could build, but your skill as a carpenter/woodworker was in how you overcome mistakes.


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