I have built some drawers for a cabinet and have discovered when I placed them in the cabinet that in the upper part of the cabinet when I place the drawer they get stuck and will
only go not place with some force. So obviously the cabinet is not completely square, In order to get the drawers to fit is there any problem with sanding down the rear half of the drawers until they fit correctly or should I remove the need space from the inside of the main box?

The space need is approximately 1/16″ from each side.

I await your advice on this matter.

Thanks
Benny