"Richard J Kinch" wrote in message
. ..
Roger Shoaf writes:

Since these sections are ordinarily
assembled by one person the *huge* force might not be so *huge*.

You are speculating about hazardous things you clearly don't understand.

The force is applied *after* assembly.

Sure it is but if the force was significantly greater than the weight of the
door, you would have a devil of a time closing it.

I believe it was Newton that said for every action there must be an equal
but opposite reaction.

From your web site you describe winding the spring. You also show a weight
of 350 pounds for the door. So at full down each side of the spring is
going to be applying about 175 pounds of force up to equal the weight of the
door.

when the door is half way up, that number will be about half as the spring
unwinds, and at 3/4 the way up will be about 1/4 of the 175pounds or perhaps
a little more because of the preload. For the sake of argument, let's say
the force was about 50 pounds.

This is like a 50 pound weight on one side of the pulley trying to lift up
one edge of the garage door attached to the other side of the pulley.

Is this what you are calling a *huge* force?

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.