Cut out the rib pattern, transfer it to aluminum plate, cut, bolt to another plate,
toaster oven, add ball bearing slide, air cylinders, solenoid valves...
This works fairly well. Put a length of plastic in the oven at 300° for about 5 minutes, take it out
of the oven with gloves, put it in the forming rig, hit the switch with my foot, hold closed for a minute, open and inspect
new collar rib.
At this rate it will take 9 hours if I don't stop for lunch. I can see why people do multiple parts
at a time.
Eventually all the ribs, with a few spares, were done.
A fairly normal support structure consisting of 2 rings made of 1/8" thick
material: top 12" OD x 8" ID, bottom 16" OD x 9.75" ID and 6 supports that were about 3.25" tall. This was solvent welded
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
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.
Below is the collar attached to the torso with a thin gasket in between.I am not
sure if I will keep the gasket but it does give an interesting effect.