squaring an out of square cabinet

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Forum topic by bloqbeta posted 12-29-2012 02:52 AM 10139 views 0 times favorited 12 replies Add to Favorites Watch
View bloqbeta's profile


19 posts in 2196 days

12-29-2012 02:52 AM

Hi everybody,

Before embarking on building my home kitchen, I decided to practice building a kitchen sink cabinet out of plywood.

I build it using the taunton press’s kitchen cabinets made easy. The plywood 3/4” was cut by the supplier on a vertical panel saw as to ensure proper dimensions and squareness.

The only thing I cut in my crappy and dangerous as hell skillsaw contractor saw was the 1/4” inch plywood back, which i doubt is square, but since it housed on a dado on the sides bottom and top I thought it wouldn’t matter.

I finished the assembly (with fasteners, no glue) and checking for squareness I saw that it was extremely out of square. I put a clamp diagonally, from corner to corner and brought it to square, but when I eased the clamping pressure it sprung back out of square.

Taking a closer look, it appears that only the left side from the front is out of square. The back side left and right is square.

The only thing that comes to mind is either the top or bottom is out of dimensions or the back is the problem.

Here are some pictures… ¿what do you think? Tomorrow I will dissasemble the whole thing and measure everything… Another question, will the eurohinges inset work with a cabinet out of square?

-- Ebanisteria Sabrosona

12 replies so far

View Dallas's profile


3599 posts in 2516 days

#1 posted 12-29-2012 03:01 AM

To check the square of the back, measure across the diagonal. They should be exactly the same.
If they aren’t the back is out of square.

-- Improvise.... Adapt...... Overcome!

View FirehouseWoodworking's profile


708 posts in 3302 days

#2 posted 12-29-2012 04:52 AM

Is the side out of square or is the panel bowed?


-- Dave; Lansing, Kansas

View mtn_goat's profile


11 posts in 2925 days

#3 posted 12-29-2012 05:56 AM

Be mindful of your thought that the back panel can’t pull things out of square. If your back is rhomboidal, your cabinet can be too, even if you technically have clearance in your dado. look for a tighter fit in one corner vs. the other as a clue.

View MNgary's profile


301 posts in 2446 days

#4 posted 12-29-2012 05:23 PM

When one side is 90 degrees to the base and the other isn’t, I check to make certain the base and top are exactly the same length and that both sides are exactly the same height.

-- I dream of a world where a duck can cross the road and no one asks why.

View kizerpea's profile


774 posts in 2396 days

#5 posted 12-29-2012 11:39 PM

first check that junky square u are checking with….


View AlaskaGuy's profile


4220 posts in 2338 days

#6 posted 12-30-2012 03:34 AM

+++++ on Jonathan’s advice.

I learned that the hard way. I cut up a whole set of kitchen cabinets (19 boxes) at one time . When I started to put them together every box was out of square. Saw blade not square to the table, had to start over.

-- Alaskan's for Global warming!

View RVroman's profile


163 posts in 2053 days

#7 posted 12-30-2012 03:37 AM

If you have not done so already I would check the size of your panels. Most suppliers here do not guarantee the accuracy of their cuts, or will only guarantee them to be within 1/2” of what was requested.

-- Robert --- making toothpicks one 3x3x12 blank at a time!

View Moron's profile


5032 posts in 3922 days

#8 posted 12-30-2012 03:46 AM

start over is the easiest and least expensive repair

or make a trapezoidal door

neither repair brings happy thoughts

that said, sometimes plywood cabinets have twisted forces within the layers of ply, and when not fastened down can twist …….the small tri-square might not be a true representation of the bigger picture so measure across the diagonals of the cabinet and see if they are the same.

the beauty of euro hinges……..they can hide what lies behind

-- "Good artists borrow, great artists steal”…..Picasso

View bloqbeta's profile


19 posts in 2196 days

#9 posted 01-01-2013 08:32 PM

Happy new year everyone,

Today, I decided to work on the cabinet, Checked the dimensions of all the pieces and they are dead on, and edges are dead on 90° to their faces.

So I went to work on the back: all the edges had bumps on the middle so I proceeded to hand plane the bump ald leave a hollow on all edges, between half and 1 thou hollow in the middle.

Also, I took away 1 mm to the length and to the width, and made it dead square.

I reassembled the cabinet and fined tuned the diagonal measurements, front and back and until there was no doubt it was the same to the mm.

THe revelation came when I tested the panels, all were bowed to a certain degree, both sides, top and bottom.

So I guess I will leave it like it is. Now, my questions:

1. Is all plywood as crappy as mine, meaning that all plywood bows so easily?

I live in an EXTREMELY humid environment and decided to make the cabinets with 3/4” plywood for this reason, melamine would puff up and MDF would certainly be worse.

2. Is there a way to correct the bow? I imagine that if you fasten all the boxes in the kitchen as a whole unit you can control the sides from bowing…

3. What conditions in the shop can help minimize bowing? I think that if you assemble the box the same day you cut the plywood would help keep the bending forces at bay, is this true?

I am not living in my house at the moment, so I had to build it in the backyard in the sun, with changing temperatures and humidity during the day, I guess this doesn’t help either.

Thanks for you help.

-- Ebanisteria Sabrosona

View bloqbeta's profile


19 posts in 2196 days

#10 posted 01-01-2013 11:06 PM

Hi Kizerpea, The square is a PEC square and it is solid, very well machined, and very acurate. I would like to own a Starret but right know a Starret is way down in the list. I am very obsesive on accuracy and I am always checking it for squareness and I am very pleased with it. My only complaint is the setting screw when you take out the ruler, it is a pain to put it back, and I think it is an issue that the folks at Starret have solved. Hope I can have one soon.

RVroman: I live in Guatemala, and it is difficult to find good supplies, suppliers and woodworking stores. Plywood, MDF, is local and you can only find it up to 5/8’. On the other hand, the best mahogany and cedar is from here, but most of the good stuff is exported to you guys, you need good contacts and thankfully I have them. There is a booming market on kitchen cabinetry in GT, so the folks where I bought and dimensioned the plywood, have found a great niche selling, cutting and edge banding for all cabinet makers, with gauranteed accuracy. They have top of the line german, and U.S. vertical saws and such. In fact, this cabinet was my first time trying this supplier and I am very pleased with the accuracy on their cutting services, but the plywood they sell is local and of the lowest quality.

FIrehouse ww: You got it right, the box is square but the panels are bowed!

-- Ebanisteria Sabrosona

View FirehouseWoodworking's profile


708 posts in 3302 days

#11 posted 01-02-2013 01:59 AM

Sorry to hear that I was correct.

I keep an accurate framing square that I use only for cabinet making so it won’t get dropped or bent. The longer framing square legs allow me to check squareness when assembled as well as looking for bowed plywood before I cut the panels. It has saved me a number of experiences such as yours.

I also try to store my sheet goods flat whenever possible, fully supported on a flat surface. Since my shop has a concrete floor, my sheet stock lies upon a one inch sheet of pink foam insulation so that it will not pick up any moisture. If you stand them up against a wall, they will bow over time. If you must store sheet goods against a wall, try storing them tight to the wall and put something heavy like a cabinet in front to keep them from bowing.

You may be able to fix your problem if you were to add a face frame of matching hardwood to your cabinet. If you cut a dado on all four pieces of the face frame, you might be able to bring the sides back into square and you’ll have a square opening for your door. Best of luck.


-- Dave; Lansing, Kansas

View fuigb's profile


492 posts in 2987 days

#12 posted 01-02-2013 02:28 AM

If an error is to be made then make it consistently. I cut matching panels ( e.g. left side n right side) simultaneously, one stacked atop the other. Or on the same sled with the same stop. Ideally the stock is flat, but there’s a point to which you may have to accept that your pieces take different paths but still end up at the same destination. I use this fail safe method because I find it easier to correct errors in the middle of a run than in a corner.

A problem that I cannot entirely shake is paneled sides not matching up after assembly of all of the rails n stiles. Like wtf, how is this possible? What can you say except that a series of tiny errors compound over a long run and errors + errors = mess. Solution: as with above, assemble each, stack, cut to desired final dimension. End result are two perfectly matched sides to a wardrobe and the 90s which truly are 90 upon assembly.

-- - Crud. Go tell your mother that I need a Band-aid.

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