Next, a fixture to assemble

Like many of us, to assemble the collar, I used Bob Greiners excellent drawings. Just glue them to a board. Next, to form a guide for the outside diameter for the collar, I cut out a circle 19.25” in diameter in some 1/8” thick sheet plastic. The idea is to have a smooth edge that a fixture can be slid along to position the ribs at each point from Bob’s drawings and at the same time be at the correct radial (in-out) and axial (up-down) position.

This 19.25” circle guide is screwed down to the board so that, as close as possible, its center coincides with the center of  the rib pattern.

Next, the support ring assembly for the ribs is located and bolted down the same way. Note that there are spacers (brass nuts actually) that hold the support up above the board so that the ribs can slip in with some clearance.

Now everything, the pattern, outer circle & the support structure is lined up with the same center point. All that is needed is a fixture to hold the ribs in place while the glue sets up.

The idea here is to locate the ribs by their outer edge instead of the inner ends. After all, its the outer edge that shows! When its all done no one will ever see the rib ends. This is slightly different from the normal design of the collar that requires that each rib be both formed identically and have accurately trimmed ends. Trimming rib ends adds a lot of work as well as adds additional tolerance problems that will definitely make the collar more irregular. By using the 19.25” circle guide and aligning only the outer edge of the ribs a much more uniform collar results. Paul Felski in the UK did his collar somewhat the same way: www.b9robotbuildersclub.com/pub/builders/scrapbooks/sb_B90203_1.html

The fixture is made from a block of plastic, aluminum plate & hardware. It is set up with its radius and edge so each rib will be pointing at the center of the assembly. The two pins are enough to do this very well. Put some glue (Household Goop) on the ends of a rib, slide it in place, slide the fixture into the rib, align the fixture with the pattern, wait for the glue to set up. Repeat. Unfortunately it can only do one rib at a time.

Goop was used instead of solvent weld to allow ribs to be repaired. While Goop is strong it is not as strong nor as permanent as a solvent welded part. If (when?) a rib breaks it is possible to remove the Goop, something that would be very difficult to do with solvent welded parts.

Here it is completed. Very nice. But I suffer from “The doer’s eye”: Every spot I even slightly messed up I remember and forever my eyes are instantly drawn to it!

With Bobs drawing and this simple fixture it was fairly easy to keep the ribs lined up. This collar weighs in at 4.17 lbs.