What would the best configuration to open and close a large metal door (wheels are on top) using a simple block and tackle system.
This seems, my good man, to be a situation where what we Canuks call a 'chainfalls' might be appropriate. I don't have a clue what the technical name for the thing is. It's essentially a differential chain pulley system (wherein two side-by-side chain pulleys are one or two links apart in size). Depending upon the diameters, you can get up to about 500:1 ratio. Most of our overhead commercial doors have very heavy coaxial springs wrapped around an axle to act as a counter-weight, and use chainfalls for opening and closing. They have an advantage in that the chain being set into a wall-mounted bracket serves as a totally irreversible locking device. A 300kg door takes about 1.5 kg's of pull on the chain to open or close, but more than a tonne of upforce from the outside to open if the chain is tucked in. The same set-up can very well be used in a horizontal situation.brewnog said:For now, I will join Danger in suggesting the research of some commercial systems, or perhaps someone else might have a bright plan.
That's definitely an aspect of their charm that can be done without. When I was at one of my previous places of employment, I spent a good portion of my days running the damned door up and down. Despite the lack of force required, the repetition resulted in a blister or two.FredGarvin said:Chainfalls are OK if you don't have to open the door too many times during the day. They can take forever to open. Closing can, on vertical doors, take your hand off if you're not careful.
davepls said:Thank you for your response. What about closing versus opening? and does side versus top of door make a difference (in the location of the pulleys)?