Square is as important as level!

    (Orginal post from the 3D Printing Experience blog) 

OK, if you have been 3D printing for more than a day you've heard the term "leveling you bed" it's not so much actually getting the bed level as it is getting the bed parallel to the plane of the extruder's movements. Level is very important so the first few layers adhere the the bed as well as having them being an equal thickness.

    But, this isn't about leveling your bed. This is about how "Square" your frame structure of the printer is. Square is all the axises being 90º from each other,  which though not as important to getting the first layer to adhere, but just, if not more important to getting items to print properly, especially if you are trying to print mechanical item that need to fit together and have reasonably tight tolerances. If you're getting prints that are leaning, or just don't fit right, it's likely you may have the frame out of square. Below is an image of the 3 main issues of out of square frame   even though the nozzle is leveled with the bed.

results of out of square frame.

(note, Z axis can be out front to back as well as the side lean displayed)

Mostly applies to Prusa i3's and such with moving Y plane bed.

   Though the above image it's very visible because I exaggerated the issues, it may be much more slight in your printer to the point it's hard to actually see, but can give problems when printing fitted parts that need to align and work together.  I have designed a simple triangle thingie that you can print to check your printer for square.  Now you can print any old box, or what ever as long as the bottom, one side and front or rear has a flat straight plane, I just personally like the triangle thingie as I think it looks cool!

Thingiverse -Triangle Square Thingie

   Now print it (or what ever) out. Once printed, take a square and check just how well your printer is doing. Honestly, its best if possible to leave the item on the bed. that way it's easier to tell in which direction/what side is out so you can fix or adjust it.

 print the little triangle thingie- leave on bed if possible

X to Z axis,  lean side to side and tilt front to back.

X to Y axis

   Now a "speed square" will work, but the combo-slide square work best in this application as it allows you to lift the bottom edge just a tad to clear any brim or border you may use to adhere the print to the bed. 

notice I lifted the edge of the rule to avoid false reading from brim

  After checking if you find something out of square you'll need to adjust it.  It's going to be widely different depending on printer model and style so I won't get into that whole thing, but you can consult your manufacturer or hit up many of the groups and forums for your particular model.

But, once you have checked and fixed any issues with your printer being out of square then you will notice not only mechanical parts fit better but also organic prints should improve in visual quality.