Crack Generator 3000 plans

Since I suddenly have so much time on my hands, I've decided to build this. I'm not entirely sure how the crank mechanism works however. From the comments, I gather they used two really long threaded rods with a bike chain going between them to allow both rods to be turned at the same time. I understand that bit, but how turning the thread actually moves the boxes eludes me. How exactly should the boxes be attached to the threads? I apologize in advance for being dumb.

Edit: I'm thinking you need some sort of flange nut on one box that will move along the thread, and then on the other box a bearing of some kind to fix it, but still let the rod spin?

Maybe something like this? I would still be using wooden tracks like in the video to support the weight of the boxes. 

That contraption is going to weigh quite a bit, you'll need some type of sliding support to allow smooth lateral movement.

Essentially, each one of your walls will need a nut (or two) mounted parallel to the sides your hands will be touching while climbing. The threaded rod will go through each nut. Your nuts must be facing the opposite direction on each of the two boxes so it will move in opposing/converging directions when you turn the shaft.

Take a look at these links to McMaster-Carr,  you'll be able to figure it out from there.

 
https://www.mcmaster.com/threaded-rods/=ef5121cd697a41bab8af7b80bc1ad5e0k8e56shw 

  mcmaster.com/gears 
 
Edit: fixed a word.

Oh neat. I didn't think about having nuts in the opposite direction. Thanks!

Hey OP, did you end up going through with this build? I'm thinking about building it as well and would love to hear how you got it done.

No, sorry. Ended up going with a more conventional crack machine. 

What was the "conventional crack machine" Zachary?

Not the best picture, but I basically attached two 2x8s to the side of a moonboard-like wall with threaded rods. 

Zachary - I was thinking of building a moonboard and mounting a crack on the side, and I ran across your image. I have a few questions if you don't mind. 

1) In the picture, what is the left 2x8 attached to (e.g., a 2x6)? 

2) how long are the threaded rods? 

3) Do those threaded rods go through just the two 2x8s (and whatever the left 2x8 is attached to), or does it go through some additional bracing? 

4) Anything you would do differently next time?

Thanks!

Richard

1. 2x4. The lumber I used was untreated, so it may look a little bigger than your typical pressure treated 2x4. 
2. 12 inch long, 1/2 inch diameter. It goes just wide enough for me to use stacked hands. 
3. The threaded rods go through the two 2x8s and the 2x4 that makes up the frame of the moonboard. Held together using just nuts and washers. 
4. I'm pretty happy with how it turned out. My only complaints are that it's annoying to change sizes and the crack isn't really deep enough for any feet first shenanigans. 

Zachary - What would you recommend to allow for feet first shenanigans? That was one of the reasons I was interested in that angle, to practice pivots, etc. 2x10s? 2x12s?

I think 2x12s would be wide enough. Just needs to be wide enough so you can fit your feet in there without your toes poking out the back. 

Here's the write-up and links to photo's how we built the thing: https://medium.com/@jeroenvanzeeland/how-to-build-a-crack-climbing-machine-db7027a407e8

Jeroen, Kudos brother. Way to go above and beyond! A most sincere thank you, which is rare on MP. Well done!

If you're going to use 2x12 probably cheaper, easier, and straighter to use LVL. Would probably have to coat it with something to make sure you don't get splinters.

Zachary K wrote:

I think 2x12s would be wide enough. Just needs to be wide enough so you can fit your feet in there without your toes poking out the back. 

I built an invert machine using 12s and some plywood but it wasn't adjustable. Ended up setting it to baggy hands/paddles. Helps me work on my dumb invert OW problems by way of forcing you to develop the core strength needed to invert at all. I would definitely do it again but would use your design to make it adjustable.