PIPE BENDER PROBLEM?

It's also under 'Tools' so don't say it's in wrong section. more plumbers would be looking here who have had same problem.

Pipe bender little used now doesn't bend the pipe.
Bought with a friend to refurb our own properties and to reduce the amount of joints needed.

Procedure:
15mm inserted in the bottom of the former invert.
the slide in bar fitted in position on the pipe then pulling the arms together no conact of the wheel on the handle with the slide in bar, and noted 12mm gap between bar and wheel what would be the cause?