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  #11  
Old 08-16-2022, 11:18 AM
Jades1 Jades1 is offline
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I watched the video...what I'm doing is way more complicated than that

So the question I have is whether the pulleys are creating an exact force that is preferable to me just being able to move it up and down with my hands and tightening with the shaft collar and using the pulley just as a 2nd safety mechanism. If a pulley does provide the exact amount of force to prevent racking than that is probably the best way forward.

I googled old school drafting table, with pulleys, etc. Not a lot came up. Is this what you're thinking? https://www.instructables.com/Build-...rafting-Table/
Where would the two cables join, such that you are pulling with one cable to tie it off. Do you have a schematic you could link?


Shade Tree Welder, when you say I need longer linear bearings, are you referring to the linear bearing unit? Maybe I could just put two of them together?
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  #12  
Old 08-16-2022, 11:25 AM
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Quote:
Originally Posted by Jades1 View Post

I googled old school drafting table, with pulleys, etc. Not a lot came up. Is this what you're thinking? https://www.instructables.com/Build-...rafting-Table/
Where would the two cables join, such that you are pulling with one cable to tie it off. Do you have a schematic you could link?

Yes, that's the one, scroll down on the linked for the "schematic".
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  #13  
Old 08-16-2022, 12:27 PM
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Quote:
Originally Posted by Jades1 View Post
I watched the video...what I'm doing is way more complicated than that

So the question I have is whether the pulleys are creating an exact force that is preferable to me just being able to move it up and down with my hands and tightening with the shaft collar and using the pulley just as a 2nd safety mechanism. If a pulley does provide the exact amount of force to prevent racking than that is probably the best way forward.

I googled old school drafting table, with pulleys, etc. Not a lot came up. Is this what you're thinking? https://www.instructables.com/Build-...rafting-Table/
Where would the two cables join, such that you are pulling with one cable to tie it off. Do you have a schematic you could link?


Shade Tree Welder, when you say I need longer linear bearings, are you referring to the linear bearing unit? Maybe I could just put two of them together?
Drafting Table: The cables are there to equalize the force you input with your hands to move the guide up and down and keep the drawing guide from racking. Each cable end is anchored to the guide. As with all cables, there needs to be some kind of mechanism to take up the slack, such as a turnbuckle, threaded end or movable pulley.

If you want to support a weight, that force will need to come from somewhere else.
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  #14  
Old 08-16-2022, 02:00 PM
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Originally Posted by Shade Tree Welder View Post
That but I think you need longer linear bearings. You are calling them cartridges, they are the linear bearings or double the number of them and mount them on a board or frame that is co-planar with your guide rails, If you go with the doubling of them have them mounted at least 6" apart on center.
Yes, longer bearings will prevent the table from jamming cockeyed.
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  #15  
Old 08-16-2022, 02:34 PM
Jades1 Jades1 is offline
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Okay, I see more of how it will work, but still not completely understanding. So if the bottom left cable ran through the bottom pulley and then the top right pulley to a boat hook (or something like that), it seems like that would still create issues, as you are just adding slack to one of the sections. Would you then need a double pulley such that slack could be given to both sections and then you tie off the two cables at one point?

How far apart would the four pulleys need to be in this case? Because it seems that if you need to tie two cables into one, you would need to run the cable for a bit before going through the final pulley (else you wouldn't have the full range of the lifting desk).
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  #16  
Old 08-16-2022, 03:34 PM
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Originally Posted by Jades1 View Post
Okay, I see more of how it will work, but still not completely understanding. So if the bottom left cable ran through the bottom pulley and then the top right pulley to a boat hook (or something like that), it seems like that would still create issues, as you are just adding slack to one of the sections. Would you then need a double pulley such that slack could be given to both sections and then you tie off the two cables at one point?

How far apart would the four pulleys need to be in this case? Because it seems that if you need to tie two cables into one, you would need to run the cable for a bit before going through the final pulley (else you wouldn't have the full range of the lifting desk).
Believe it or not, math works. Pull down one inch on one cable and the opposite end moves one inch. EXACTLY one inch unless it's under extreme tension and stretching.

Both ends of both cables are tied into one structure, be it a bar, beam, flat sheet or whatever.

Once the cables are tensioned up, you'll grin from ear to ear.

Can't read your mind, so the length of the rope needs to be from the cow to the barn.

Did you see the schematic?
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  #17  
Old 08-16-2022, 04:06 PM
Jades1 Jades1 is offline
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I didn't see a schematic...just the pictures from his project.

Maybe I'm misunderstanding something, but you are talking about a closed system, right? Where, as you write, "Both ends of both cables are tied into one structure." In my question, I was wondering if it was possible to take that and make it not only keep everything parallel, but to lift (and hold) it as well.

Regarding length of rope/cable: I guess what I'm wondering is the four pulleys would be at the four ends of linear rails--is that correct?
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  #18  
Old 08-16-2022, 07:04 PM
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Your link: Step 2, Theory of Operation
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  #19  
Old 08-17-2022, 10:55 AM
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Quote:
Originally Posted by Jades1 View Post
I didn't see a schematic...just the pictures from his project.

Maybe I'm misunderstanding something, but you are talking about a closed system, right? Where, as you write, "Both ends of both cables are tied into one structure." In my question, I was wondering if it was possible to take that and make it not only keep everything parallel, but to lift (and hold) it as well.

Regarding length of rope/cable: I guess what I'm wondering is the four pulleys would be at the four ends of linear rails--is that correct?

Quote:
Originally Posted by arizonian View Post
Drafting Table: The cables are there to equalize the force you input with your hands to move the guide up and down and keep the drawing guide from racking. Each cable end is anchored to the guide. As with all cables, there needs to be some kind of mechanism to take up the slack, such as a turnbuckle, threaded end or movable pulley.

If you want to support a weight, that force will need to come from somewhere else.
See above quotes.
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  #20  
Old 08-18-2022, 11:55 AM
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Quote:
Originally Posted by Jades1 View Post
I didn't see a schematic...just the pictures from his project.

Maybe I'm misunderstanding something, but you are talking about a closed system, right? Where, as you write, "Both ends of both cables are tied into one structure." In my question, I was wondering if it was possible to take that and make it not only keep everything parallel, but to lift (and hold) it as well.

Regarding length of rope/cable: I guess what I'm wondering is the four pulleys would be at the four ends of linear rails--is that correct?
You put the pulleys on the holding object, and attach the moving object to the cable. You can put the pulleys wherever you want, so long as they're equally spaced in relation to your task. Unless you find a way to 'lock' the cable in place any pressure you put on the desk will allow it to move. If there is substantial tension, it will serve as a lock but the likelihood is that you could end up breaking parts off your mechanism when something heavy is set on the surface.

Another way to go about it is via half the cable system of an Etch-a-Sketch. The knob/dial would allow you to twist it to the necessary height.

Schematic:
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Last edited by dubby; 08-18-2022 at 12:15 PM.
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