Richard J Kinch writes:
Steve Barker writes:

This is wrong also! The number of quarter turns is dictated by the
weight of the door AND the caliber / length of the spring.

You're both wrong. Full turns equal the height of the door travel, divided
by the drum circumference, plus about a half a turn. Opening the door with
insufficient winding will lead to slack cables hopping off the drums, and
then disaster, so the extra half turn is important.

The number of turns = door height / (drum diameter * pi).
Should be about 5 for most doors.

If you start with the door in the full up position, you
can get everything connected without tensioning the
springs. Then lower the door and increase the tension
to fit and suit. You should be able to readily lift
the door with one hand when it's adjusted correctly.

Tensioning the springs as much as possible may allow
launching the door into low Earth orbit.