How do you square the supers you build?

[efmesch]

Winter is on its way and with it the season for building new equipment. 
Assembling new supers by fitting the sides into their slots doesn't always guarantee that they sit perfectly on the super below. 
There must be some simple way to make sure that all your supers come out perfectly. 
How do you do it?

[Perry]

Good question.
I usually square them with an actual square, and then as I stack them I place a heavy weight on top of the stack ensuring nothing moves until the glue dries.
The marine battery in the pic gets awfully hard to lift as the stack gets higher. 

[efmesch]

Do you put in  the nails/screws/staples before or after the glue sets?

[Perry]

I glue them up, screw everything together, one final check for square, and then on the stack with weight. If anything goes askew in the process it shows up when I place it on the stack and I can adjust before adding the weight.

[Papakeith]

I pretty much do as Perry does. 
I square up the first one and then square up the next one and place it on top of the stack.  If it is a bit off I'll adjust until the stack is straight. Then I haven't bothered with a weight yet, but I think that may be a good idea to get them to set completely flush to one another.
Once they are set I place them up on a shim and roll the paint on.
I put them together with glue and staples.  So far so good.

[LazyBkpr]

   I have a wooden table in the middle of my wood room.. I built a jig out of 2x4 scraps on that table and made sure the JIG was perfectly square..  I drop in my boards, glue and nail, pull them out of the jig and set them on a stack like Perry does.

[pistolpete]

I keep checking mine for square with a 60cm framing square as I'm assembling.   If need be, I put a clamp on from corner to corner to hold it square while the screws are going in and until the glue dries.  I'm not shy about shaving a touch here or there with a hand plane to make them flat.

[apisbees]

squareness can be controlled with a jig, square, checked corner to corner, with a square but having the super sit flat and not rock corner to corner depends  on 2 things. The board not having a twist, and the ends being cut square.

[Barbarian]

A slight alternative.

I use nails and glue. Before the glue has set, I put the super on a flat worktop then use a rule to check the diagonals are equal. If unequal, then a little nudging to square up.

[efmesch]

Barbarian, You Owd Codger,  you return me to my days of High school geometry.   

[Lburou]

Important skill to make things square so they fit well in a stack Ef.  I made one of these jigs and things stay pretty square.  Then, stack them with a weight on top like everyone does.   

At the same time, I made one of these frame jigs from robo's web site.