Square a bookcase

[Chris Hibler]

Hi Folks,

I'm really new to woodworking and I recently thought I would try making a bookcase from plywood. The problem I'm having is, I'm not sure how to get it square. 

I had it pretty much built using the Kreg Jig but it turned out to look more like a parallelogram, the sides were not straight.

I have it disassembled now and I could really use the help of the community to teach me the proper way to make sure the bookcase is straight/square.

Thanks in advance.

Chris

[Tim E Daniels]

If all your lengths are the same for your sides, and it is a parallelogram, measure your diagonals. They should both some out to the same length

[Derek]

I'm no expert... but here are a few ideas:
1. Adding a plywood backer is a great way to make sure it's square: http://www.ehow.com/how_5964661_square-bookcase.html
2. A face-frame can accomplish the same goal.
3. Measure from corner to corner diagonally... the measurement should be the same before you tighten down the screws/glue, etc.

[Tim E Daniels]

A good example from JerryAlfaro is