How to fix an out of square cabinet?

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Forum topic by BryanB posted 11-08-2009 04:40 AM 10417 views 0 times favorited 7 replies Add to Favorites Watch
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5 posts in 3867 days

11-08-2009 04:40 AM

Topic tags/keywords: cabinet mdf problem square sag question

Where to start…. I am building some cabinets and bookshelves for our family room. This is my first real woodworking project as an adult. Why start small, right?

So I assembled the first base cabinet and it is out of square! Specifically only 2 opposite corners, the other 2 corners are square. Can it be fixed and if so how do I fix it?

In addition, I also realized the top and sides are bowed about 1/8” over 36”. I used 3/4” MDF because I am intending on painting it. The dimensions are 36”w x 32”h x 24”d, so I know I’m pushing the limit of what MDF can handle. Now I’m wondering why I didn’t choose a pre-primed or pre-finished plywood.

Any and all help is much appreciated! Thanks in advance!

-- Bryan | San Jose, CA

7 replies so far

View bruc101's profile


1200 posts in 3542 days

#1 posted 11-08-2009 06:47 AM

The only MDF I use is for templates so can’t offer much about MDF. What kind of joinery did you use and did you put a back in the cabinet?


-- Bruce Free Plans

View TopamaxSurvivor's profile


18272 posts in 3676 days

#2 posted 11-08-2009 06:51 AM

How much is it out of square? Is it noticable and distracting?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View BryanB's profile


5 posts in 3867 days

#3 posted 11-08-2009 08:20 AM

I used dadoes and rabbets with glue and screws, but haven’t put the back in yet. Maybe the back will help true it up?

It’s about 1/4” over 2’, so I don’t notice it but am concerned that once I keep building it out with the face frame and bookshelves on top that I’ll regret not fixing it now.

-- Bryan | San Jose, CA

View Rick  Dennington's profile

Rick Dennington

5864 posts in 3195 days

#4 posted 11-08-2009 08:43 AM

I’m like bruc101: I don’t use MDF for building cabinets,etc. But MDF is usually pretty flat and stable, and not bad to bow out or warp. it’s just paper,basically. Sounds like you may have some cuts or measurements wrong somewhere. I think with a 1/4” out, if you rabbit the back edge and put a back on it, it should help it square up some. Once the back is on, check your diagonal measurements corner to corner. Sometimes you can pull it back into square with clamp pressure. Good luck.

-- " At my age, happy hour is a crap and a nap".....

View huff's profile


2828 posts in 3286 days

#5 posted 11-11-2009 12:26 AM

Rick gave you some good ideas. Make sure your face frame is square when you build that and try to align the cabinet to the face frame as close as possilbe. You can sometimes pull a cabinet back to square. This may rack your cabinet, so I would be more interested in getting the front aligned as square as possible and allow the back to be out of square a little if need be. This is a great learning experience, but not a huge deal. I’ve spent years learning how to build a square box, on to find out I’ve never found a perfectly square house to put it in. LOL. That’s why I love working with curves!. Good luck and I’ll bet your next cabinet will be better.

-- John @

View a1Jim's profile


117095 posts in 3578 days

#6 posted 11-11-2009 12:49 AM

Hey Bryan
I agree with Rick and huff putting a squarely cut back into a rabbit should help allot an any thing left over that’s out of square can be tweaked with the face frame. of course the best way is when gluing to check square top and side and clamp with a shop made or store bought square to hold it in square when the glue is drying one in each opposing corner

-- wood crafting & woodworking classes

View BryanB's profile


5 posts in 3867 days

#7 posted 11-11-2009 01:25 AM

Thanks everyone for all the great suggestions! I’m going to try to get some time in the “shop” this week and see what happens.

-- Bryan | San Jose, CA

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