Pulley system for opening garage door

[Whiskeymike]

My shop has a 10 foot tall pull up door with no automatic opener. It's not bad, but the wife is not a fan. I was thinking of mounting a pulley up top and running a rope down to make opening the door easier. How does the diameter of the pulley affect the ease of pulling up the door? Where would be a good place to purchase a pulley that does cost as much as a jack shaft opener? On amazon, I saw large pulleys, but they didn't have a mount, just the wheel itself.

Also, is there a config of using two pulleys to use the rope to make it open and close? Right now I have a 6 foot rope attached to pull it down, but all in one would be great.

 

[DIC]

You could hang up a ****** block


http://www.harborfreight.com/4000-lb-capacity-lifting-block-60644.html

 

[wssix99]

You'd need a system with multiple pullies to get a mechanical advantage. Is the problem that it's hard for your wife to lift or because she needs to bend over?

The springs are what makes the door easier to open. How old are yours currently on the door?

 

[nehog]

(seriously, a picture is likely to generate better suggestions!)



(Uh, picture of the door not the wife!)



(OK, a picture of the door and the wife!)

 

[jstroede]

http://www.garagedoorstuff.com/product/garage-door-chain-hoist-wall-mount-gear-reduced-2000r/

You are looking for a chain hoist. You have to work a little to adapt it to hollow shaft but it can work.

John

 

[rslaback]

The size of a pulley does not effect the mechanical advantage of it at all.

 

[egdede]

The size of a pulley does not effect the mechanical advantage of it at all.

I think it does; see 'gearing ratio'

 

[kbs2244]

The spokes of a pully are just levers connected by a rim.
The length of a lever, and thus the dia of a pully, plays a huge part in its mechanical advantage.

 

[rslaback]

I think it does; see 'gearing ratio'

It doesn't actually. It makes the coefficient of friction less in order to spin it compared to a smaller pulley, but it doesn't actually change the mechanical advantage. The only way that a pulley creates a mechanical advantage is if it is able to move with a load.

If you look at the example of a block and tackle system, the pulleys on top that remain in the same location, the pulleys on the bottom that are able to move with the load will each reduce amount of force required and increase the amount of rope that needs to be pulled.

http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm

http://en.wikipedia.org/wiki/Mechanical_advantage_device

 

[rslaback]

The spokes of a pully are just levers connected by a rim.
The length of a lever, and thus the dia of a pully, plays a huge part in its mechanical advantage.

I think you are confusing the use of a pulley and the use of a wheel and axle.

In a wheel and axle, the circle is solidly attached to a smaller inner rod, In a pulley the circle is able to freewheel on the axle.

If you are talking about applying a force to the outside to increase, the force on an attached axle (like a doorknob), yes. In that case the actual fact that a full circle is present is irrelevant.

However, in this example a pulley is begin used to change the direction of a rope. The axle isn't connected to the outer pulley (or in this case, there is a bearing to allow it to free spin) so the diameter of the pulley doesn't matter.

 

[JakeKohl]

A pulley only turns a rope. If you combine pullies into a system with purchase, then you get additional force for your effort. A 2:1 system will double your force and double your pull length. 4:1, quadruples and so on. The diameter of the pulley in this type of system does affect friction and typically, smaller diameter pullies are meant for smaller diameter ropes. I sail a lot and design rigging systems for sail control. Whatever you do, don't look for your hardware here. You'll be better off buying an opener.

 

[Rubber_Duc]

Sorry if I missed this somewhere in your post as to why, but why not just put an opener on it if it is used a bunch especially by your wife? I'm thinking it would be easier than fabricating a pulley system unless I missed something, if so sorry and disregard.

 

[wssix99]

I think it does; see 'gearing ratio'

The spokes of a pully are just levers connected by a rim.
The length of a lever, and thus the dia of a pully, plays a huge part in its mechanical advantage.

This would help if you were turning the shaft or a crank by hand. When you are acting on the rope, the force required is the same - it can just be put to work in another direction.

 

[Norcal]

There was a used bldg. material store that had single phase roll up door openers for $50 ea. Too bad did not know anyone at the time who needed them, place has since closed.

 

[srmofo]

I think you are confusing the use of a pulley and the use of a wheel and axle.

In a wheel and axle, the circle is solidly attached to a smaller inner rod, In a pulley the circle is able to freewheel on the axle.

If you are talking about applying a force to the outside to increase, the force on an attached axle (like a doorknob), yes. In that case the actual fact that a full circle is present is irrelevant.

However, in this example a pulley is begin used to change the direction of a rope. The axle isn't connected to the outer pulley (or in this case, there is a bearing to allow it to free spin) so the diameter of the pulley doesn't matter.

You are assuming that pulleys can't be permantly attached to the inner shaft. Think of alternators, pumps, etc. Not all wheels are fixed either. Really you are just playing semantics with words . assuming the op just wants to fix a pulley to the jachshaft. That's certainly not going to be free spinning....now if he makes a loop the pulley at the bottom will be free spinning and will have no mechanical advantage

 

[rslaback]

You are assuming that pulleys can't be permantly attached to the inner shaft. Think of alternators, pumps, etc. Not all wheels are fixed either. Really you are just playing semantics with words assuming the op just wants to fix a pulley to the jachshaft. That's certainly not going to be free spinning....now if he makes a loop the pulley at the bottom will be free spinning and will have no mechanical advantage

The systems that you describe are wheel and axle systems. The idler in that belt system is the only true pulley. Wheels that are not fixed do not provide any mechanical advantage to a system (other than the moment of friction previously mentioned).

You are making the assumption that the op was talking about mounting a wheel on the end of his jackshaft to lift the door. Others were assuming he was talking about mounting a pulley near the top of the door and then connecting a rope to the bottom so that the door is opened by pulling down on a rope instead of up on the door. Until he clarifies no one really knows for sure. That is why until now I haven't said squat about if it will work in his application.

Call it semantics if you want. There are many people who assume that if I have larger pulleys in my block and tackle that it has a greater mechanical advantage than if there are smaller pulleys. All I am trying to do is clarify that is not the case.

 

[srmofo]

The systems that you describe are wheel and axle systems. The idler in that belt system is the only true pulley. Wheels that are not fixed do not provide any mechanical advantage to a system (other than the moment of friction previously mentioned).

You are making the assumption that the op was talking about mounting a wheel on the end of his jackshaft to lift the door. Others were assuming he was talking about mounting a pulley near the top of the door and then connecting a rope to the bottom so that the door is opened by pulling down on a rope instead of up on the door. Until he clarifies no one really knows for sure. That is why until now I haven't said squat about if it will work in his application.

Call it semantics if you want. There are many people who assume that if I have larger pulleys in my block and tackle that it has a greater mechanical advantage than if there are smaller pulleys. All I am trying to do is clarify that is not the case.

Its semantics. I don't know anyone calling the non drive wheels on their car pulleys, and can't ever recall someone calling their alternator pyllwy a wheel..

But yes you are correct in that a large free spinning pulley does nothing except adding contact area. Kinda thought that was a given considering most of us have been through a 5th grade science class.

I assumed he wanted to mount it to the jackshaft because he was asking about mechanical advantage, then he compared the "wheel" to an opener, and then also discussed finding the mount for it. What do I know though, its just my tale in deductive reasoning.

Op. I suggest looking at McMaster-Carr. You could probably even use a cable drum if the rope is tensioned tight enough. Assuming you want a mechanical of course. If not head to Lowes buy 2 cheap pulleys. Mount 1 high, 1 low then attach the rope to the door. Might want to pick up some gloves because its going to wear you out trying to lift that if the springs are not set properly

 

[Whiskeymike]

I'll see about taking a pic today.

The difficulty is the weight of the door, not bending over. Also, trying to get the door all the way up/open is difficult. Normally have to take a broom to get it all the way open so we can reach.

Door is 8 years old. Seems in good working condition.

I originally was going to put a jack screw opener in, but I'm lazy and would rather work on my jeeps than mount and wire up the opener. A pulley seemed like it'd be a half hour, brownie points with the wife, done. But it sounds like it's going to be more complicated.

I though pulleys were how they did it before there were openers, no?

 

[rslaback]

I'll see about taking a pic today.

The difficulty is the weight of the door, not bending over. Also, trying to get the door all the way up/open is difficult. Normally have to take a broom to get it all the way open so we can reach.

Door is 8 years old. Seems in good working condition.

I originally was going to put a jack screw opener in, but I'm lazy and would rather work on my jeeps than mount and wire up the opener. A pulley seemed like it'd be a half hour, brownie points with the wife, done. But it sounds like it's going to be more complicated.

I though pulleys were how they did it before there were openers, no?

Before there were openers, a sprocket was usually mounted to the torsion bar and another below near the floor. Then a chain was looped between the two. You'll need the full loop of chain because of the need to go up and down and that you do not have the room to mount a 3' sprocket on the end of the torsion bar (which is what it would take to get 10' of door movement in a single rotation). It'll be easier to put in an opener.

If you only want to take care of getting the door up that last little bit then a simple pulley mounted to the wall with a rope tied to the bottom roller will do. You won't get any mechanical advantage out of it but you won't need a broom handle either.

 

[wssix99]

The difficulty is the weight of the door, not bending over. Also, trying to get the door all the way up/open is difficult. Normally have to take a broom to get it all the way open so we can reach.

It shouldn't be like this. It sounds to me that you have a balance/spring problem. If it's that hard to open, it could burn out a garage door opener if you were to put one up. Even they require an easy-opening door.

 

[In The Doghouse]

You should adjust the door spring tension so that the door will stay in place when it is half way open plus lubricate everything. Then opening and closing is very easy no matter the weight of the door.