I present to you my own hand cranked, laser cut marble machine. These are available to purchase as kits, for self assembly and I intend to run some local workshops for them too. The kit includes all the laser cut wooden parts, the nuts and bolts, and enough balls to fill the machine up and spares (8). Assembly instructions can be found here http://tinyurl.com/MarbleMachine1
A long time ago in a blog not so far away (this one actually) I ran a project where I laser cut one item per day for 365 days. While I was making the machine triggers and before I'd committed to running my own Donkey Kong machine there was a suggestion that I should be making kits like this to sell on the day. I gave it a whirl and failed and if it couldn't be cut in a few days then it was a hindrance to the 365 project so it went on the back burner.
I recently picked it up again for two reasons, one it's a nice idea and makes a fun toy and secondly I need to investigate ball lifts for the eventual recreation of Donkey Kong. In the meantime Michael Henriksen from BustedBricks created this awesome, hand cranked, laser cut, marble machine, which is a great little kit too.
I don't want to steal his thunder or jump on his bandwagon so if you're only going to buy one kit, buy his, but if you're starting a collection of machines then buy mine aswell. (The price is similar for both machines)
7 projects/ 10 weeks
The main feature of this marble machine is the ring lift. Three stacked pieces of wood mean that the holes the balls are sat in are actually sloped. When the ball enters at the bottom it wants to stay inside the ring, as the ring is flipped upside down the slope is reversed and it wants to push the ball out of the ring. The balls then run down a 5 loop spiral and back into the bottom of the machine ready to go again. The machine holds 6 balls comfortably but a few more could be held in the lift at any given moment.
As you can see the balls are pretty free running and reliable. Putting multiple balls down the spiral too close together can cause a bit of a jam but I've left the handle small so it's a lot of effort to do that. The machine was designed tested with catapult ammo quality balls in mind (about 9.5mm wide) so cheap to replace should you lose any.
Pictured above is the evolution of the design in it's current form. Not being very successful before trying to design everything up front I took the approach of cutting and modifying parts as I went along. The process was much more fluid, got through far more material but probably averaged out on a cost/time basis.
The spiral needs a little bit of tweaking to make sure all the loops are equally spaced and free running. The initial transition from above the rails to alongside the rails is made easier by widening the track but it can still have a tendency to jump a loop. To this end only the top loop is fixed to the frame, the other loops are held apart by the frame but can be moved back and forward as required and then glued into place.