Anyone know how to keep cut square when hack sawing

[jonte]

Please forgive me if this has been asked many times before, but I'm curious to know that when the square tubeing used for the chassis is cut with a hack saw, how do you ensure a square cut without resorting to files/lenishers/grinders etc. to square it up?

In eager anticipation of a reply confirming that this can be done, I'm taking up weight training to strengthen the forearm muscles of my cutting arm

Jonte

PS.... came across cutting guides for use with round tubeing whilst surfing but nothing so far for square stuff.