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Warped Plywood Cabinet Carcass - Help!

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Forum topic by SuperBee18 posted 06-23-2016 12:18 PM 610 views 0 times favorited 11 replies Add to Favorites Watch
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SuperBee18

5 posts in 167 days


06-23-2016 12:18 PM

Topic tags/keywords: plywood warp cabinet carcass walnut

Hey All,

I’m setting off to make the first of 6 cabinets to refinish my kitchen. I bought 3/4” walnut plywood from my local hardwood store and started to build the first cabinet carcass. I was able to get it assembled with one stretcher in last weekend and now that I am back at it the warp is pretty bad.

5/8” over a 30” span!

Questions are…
1. Can it be fixed? I wetted the concave side and set cinder blocks on it over some furring strips and not much changed in the couple days but it has been humid.

2. If I did get it straight will it just warp again once installed?

3. I see the wood itself is dated 6/6/2016. Is it too fresh/wet from manufacturing?

4. Would the MDF core be the way to go?

Any help/insights would be greatly appreciated!

Thanks
Brian


11 replies so far

View bondogaposis's profile

bondogaposis

4030 posts in 1815 days


#1 posted 06-23-2016 12:30 PM

5/8” over a 30” span, is too much. You’ll never get that out. You are wetting down plywood? Best to start over.

-- Bondo Gaposis

View Lazyman's profile

Lazyman

695 posts in 851 days


#2 posted 06-23-2016 12:30 PM

Not sure that wetting is the way to go here. It might cause the plys to separate or the glue on the joints to let go. Post a couple of pictures of the construction and warping and maybe someone will come up with a better approach.

Were the panels flat before you cut them? Did you notice any warping after cutting but before assembly? How are they joined, (screws, glue, dados. etc).

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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SuperBee18

5 posts in 167 days


#3 posted 06-23-2016 03:36 PM

I googled “flattening plywood” and quite a few returns mentioned wetting the convex side with a spray bottle and then drying it over furring strips however – it didn’t help much.

I’m using pocket screws. The panels were NOT totally flat flat when I cut them so I constructed the cabinet convex to the inside figuring the stretchers might help. I placed some stretchers in the a.m. and then clamped it. I’ll try to get it out in the sun as soon as that happens and go from there. But at $150+ a sheet I can’t really afford to scrap too many of these.

Here’s a pic showing the warp.

With a drawer up top I then wanted a slide out shelf below.
Maybe I place a perm full size shelf just below the slide-out to keep the dimension?

View pintodeluxe's profile

pintodeluxe

4856 posts in 2277 days


#4 posted 06-23-2016 06:33 PM

Well, plywood does bend and warp a bit. It is usually not a problem with plywood cabinets, because of the joinery that holds everything together. Rails and face frames ensure that everything is flat and square in the end.

I wouldn’t mess with the water / sun business to flatten it. Just use joinery that forces is flat. I typically use dados and rabbets for the case, and attach the face frame with biscuits.

I guess if you were planning to build a frameless cabinet you would be in trouble, but with a faceframe I think you’ll be fine.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View CharlesNeil's profile

CharlesNeil

1610 posts in 3335 days


#5 posted 06-23-2016 06:36 PM

Pintodeluxe, go it right

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SuperBee18

5 posts in 167 days


#6 posted 06-23-2016 06:38 PM

Thanks Pintodeluxe – I hear ya loud and clear.

But I am looking to go frameless.

View GregD's profile

GregD

783 posts in 2600 days


#7 posted 06-23-2016 06:56 PM


Well, plywood does bend and warp a bit. It is usually not a problem with plywood cabinets, because of the joinery that holds everything together. Rails and face frames ensure that everything is flat and square in the end.

I wouldn t mess with the water / sun business to flatten it. Just use joinery that forces is flat. I typically use dados and rabbets for the case, and attach the face frame with biscuits.

I guess if you were planning to build a frameless cabinet you would be in trouble, but with a faceframe I think you ll be fine.

- pintodeluxe

+1

Installation is another opportunity to pull things into (or out of) square.

There was a time it seemed that only the cheapest grades of plywood would curl like that. And then for a time I could find domestically produced plywood that rarely had that problem although at 1.5X to 2X the cost of the imported stuff. More recently I can’t find any plywood that doesn’t curl like that with some frequency. The problem seems to trace back to a ply layer where adjoining pieces overlap. Better to have voids, IMHO, but you typically don’t get a choice.

The bottom line is that the only way you can ensure that a plywood is going to be flat & square is to build it into a structure that forces it to be flat and square.

-- Greg D.

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SuperBee18

5 posts in 167 days


#8 posted 06-23-2016 07:21 PM

Thanks Greg D.

Thanks for all of the comments!

View Lazyman's profile

Lazyman

695 posts in 851 days


#9 posted 06-23-2016 10:19 PM

If it will fit with the design, I’ve see a square frame at the top that pulls all of the corners at the top together and gives them regidity, especially on cabinets with frameless doors. You may still have some bowing in the middle so you may have to wedge something in there, at least temporarily while you pull it all together. If you are going to have a shelf anyway, you may want to install that at the same time you are attaching the top frame or you may have a heck of a time getting it in there later.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View JBrow's profile

JBrow

818 posts in 384 days


#10 posted 06-23-2016 11:28 PM

SuperBee18,

I am guessing that the photo shows the base cabinet with what will become the front of the cabinet closest to the camera. I would think that ideally adding a top or at a minimum a piece about 3” wide at the front top between the two sides would straighten the plywood, at least good enough to proceed. If you cut a scrap piece the exact width of the cabinet measured at the back and clamp the scrap piece to the top front, you can judge whether this idea will help.

If the scrap piece clamped into place works, then perhaps a top could be added to the cabinet which would not only straighten the plywood but also add rigidity to the box, especially since the cabinet is frameless. The top would not need to be expensive plywood since it will never be seen. Holding the top down a bit from the top edges of the back and sides will keep the top from interfering with countertop installation. But a 3” wide strip at the top front similar to what was installed in the back would probably work.

I doubt any efforts normally effective in taming solid lumber suffering from moisture related movement will be effective with plywood. MDF core plywood should be more stable and flatter, but it is messy to cut and would not hold screws as well as plywood. Since the kitchen is a wet location, I would personally avoid MDF core plywood at least near the floor.

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SuperBee18

5 posts in 167 days


#11 posted 06-23-2016 11:42 PM

Hey JBrow,

I think you may be right or at least I like your thinking. I came home today after it being clamped all day with some 4” stretchers and with a straight edge on the outside they looked pretty good.

I bought the wood and I won’t be out anything to finish so I think I’ll do just that.

I’ll post pics of the results.

Thanks all for your input.
It’s much appreciated.

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