Carbon fiber magnetic ball joint jig for the Cerberus, Cerberus Pup, and other Rostocks

This jig is used to make consistent length magnetic ball joint arms for the Cerberus, Cerberus Pup, and other Rostock deltabot printers.

Requirements:

1. 3/8" steel ball bearings

2. 3/8" x 3/8" cylindrical neodymium magnets

3. Carbon fiber shafts, such as arrow shafts

4. High-strength glue capable of bonding metal to carbon fiber (I used Loctite Metal / Concrete epoxy, others have used JB Weld)

Print two and mount them onto a length of wood at appropriate distances using screws.

NOTE:

• The provided STL uses a 7.28mm diameter carbon fiber rod in the model. If your CF rod has a different diameter, download the SCAD (http://www.thingiverse.com/download:334677) and edit it in OpenSCAD, adjusting the cf_rod_dia variable appropriately.

• Assembly instructions are in the Instructions (http://www.thingiverse.com/thing:176647/#instructions) section.

The way I did it to keep the epoxy from getting all over the place is I glue one ball at a time using the following procedure:

1. Put a 3/8" x 3/8" neodymium magnet into each jig piece
   
2. Put ONE ball into one of the jigs (keep the other one out)
   
3. Mix a pea-sized blob of two-part epoxy
   
4. Carefully scrape all of the epoxy into the inside of one end of the hollow CF rod
   
5. Sit the jig vertically so the one with the ball and magnet are on the bottom
   
6. Place the end WITH the epoxy in it against the ball at the bottom of the jig (since all of the epoxy is inside the CF rod, there should be no squeeze-out)
   
7. Place the second ball into the other end of the CF rod and rotate it into place at the top of the jig
   
8. Let it sit 30-60 minutes before performing the operation on the second ball.
   

When you do the second ball, rotate the jig so that the second ball is now at the bottom and repeat steps 1-8.

What this does is uses gravity to let the epoxy flow down to the ball and stick to it. It's slow, but it works. :)