On Tue, 6 Feb 2007 12:29:29 PST, (Everett
M. Greene) wrote:

Richard J Kinch writes:
Everett M. Greene writes:

And what's wrong with it?

Everything. Method and results.

Very enlightening.

Method:

C = pi * D (geometry 101)

Unstated assumption of D = 6"

turns = distance / C

Results:

approx. 5 turns. Actually, less for typical 7' garage door

Now what's wrong?


Your objective? You appear to be trying to arrange the
spring tension to be zero when the door's fully raised.

What you should be trying to do is match the spring
tension as closely as possible to the load that the
door puts on the spring through it's entire range
of motion, while never letting the sum of forces
be small enough (or negative) to let the door bind
when you're trying to let it down. That is,
if the door has an automatic hoist. If it's all
manual, then you need the spring to EXCEED the
applied weight of the door in the up position.