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AndyCart
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For once, I may be ahead of you! I'm half way through printing the CP-I rod holders and effector plate, and plan to use some leftover 5/16" steel spheres from my Johann recirculating ball bearing carriage experiment to ride in the 10mm cups. I think that shock cord is the way to go, but we'll see once I have the last two rod holders printed.....
Pictures please :-)
Here are the results of my failed experiment. My current Delta RepStrap uses 1/2 inch (12.7mm) spherical magnets with cupped steel SHCS on the ends of the rods as the sockets. My initial thinking was that I was going to toss some leftover 5/16" steel spheres into the CP-I's effector plate sockets loose, then put my current rods on top of them for testing. Sure, there would be slop, but it was only a proof-of-concept. I changed my mind, and decided instead to use CA to attach 1/2" plastic spheres to the sockets using CA instead, and then use my existing rods on the plastic spheres.
Here is the effector plate with spheres hanging from a shock cord to each carriage (note the CP-I upper bracket): :D
Getting two rods in was relatively easy (the blue painter's tape is holding a bit of wax paper under each screw for lubrication):
After the third rod, the effector plate kept wanting to twist from the shock cord tension, so I had to dedicate a hand to holding it straight from then on. On multiple attempts, I was trying to insert rod #5 when one of the others would fall out and hit the floor. Since that meant letting go of the effector plate to retrieve it from the floor, I had to start over from scratch. I'd post pictures or video, but you can Google "keystone cops" for a better slapstick comedy routine.
Long story short, one of the major benefits to magnetic ball joints as used on the CP is simple effector plate and hotend maintenance. I can have the effector plate off in 15 seconds, and back on again in 30 seconds. Even with quick disconnect hooks on the shock cord, it is darn near impossible for one person to get six rods in place using a non-magnetic, tension-based retention system. It can probably be made a bit more simple by using deep sockets with the spheres attached to the rods, or maybe by crafting some removable rod holders for doing the installation. I'm at the point in my life where saving a few dollars by not using magnetic spheres isn't worth the hassle, and will be ordering another batch of 1/2" spherical magnets for this new effector plate as soon as I post this message.....