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 After some experimentation,
the dome construction method that works best for me has been the fast
machee and spackle method (I'm fibreglass averse, but also like to do
things myself). Bill's dome was made of newspaper, and I didn't get a very
good bottom edge. The new dome is still not perfect, but much better than
Bill's.
Bill's dome plug was a 1/2" too small, so I made
another one. this time I drew a circle on the base board of the right
diameter and made sure that the template stayed on the line as it rotated.
 The key with fast machee is to use it stiff, and give it
plenty of time to dry: a week to 10 days is needed. I've had domes warp if
they're dried too quickly with a fan heater.
When spackling the dome, I went around the lower 3"
of the dome with a straight edge, which helped keep the surface nice and
smooth.
After sanding I sprayed it with a heavy wall primer (Kilz
brand in the US) and then used automotive primer and paint over that. In
case anyone's wondering about the strength of a fast machee dome. Here's a
picture of me standing on one! |
MOUNTING THE DOME |
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With Bill, I used the
classic centre pivot method to mount the dome. With Dirk I decided to go
for a pivotless dome, to give me a little more headroom, as I'm a little
over 6' tall, and Bill is cramped inside for me. |
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I stacked up two
wooden rings, cut on a router so they are perfectly circular. |
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The top of the neck
bin has the conventional four aircraft wheels in a vertical alignment, but
also four additional wheels in a horizontal alignment to stop the dome
from moving sideways (instead of the central pivot). They're positioned so
they fit exactly inside the larger ring. |
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I mounted the eye pivot platform
slightly above the disks on spacers to give the brackets room to go
underneath it. This allows the dome a full 360 degree rotation (at least
until I trail any wires downwards(!). |
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Here are some top views to show
the arrangement of wheels.
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The brackets I used were
L-brackets and were too long, so I twisted them in a vice and mounted them
at a 45 degree angle. If I was doing this again I might make the hole in
the top of the neck bin small enough so they fit right. |
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getting there
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wearing a temporary dome
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THE EYE |
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Dirks eye is made
very much like Bill's. One difference is that I cut the eye disks using a
router rather than a hole saw. The hole saw tends to melt the edges of the
acrylic, whereas a router produces a nice clean cut (it's in contact with
the plastic for much less time). I also cut 2", 3.5" and 4"
disks, rather than the specified 2", 3" and 4" disks. This
produces a circular profile at the size rather than a diamond shaped one. |
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Bill's hole sawn eye disks
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Dirk's routered eye disks
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Here's the jig I made
for cutting the eye disks, and the set of disks I made with it. Another
advantage of this method is that you don't need a new hole saw for every
disk size you want to make... |
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 Notice
here that the threaded rod that goes through the eye pivot is mounted
1/4" above the centre line.
With Bill I had it go through the centre, and then I had
to arrange for two mounting bolts each going 1/4" into the pivot,
which was much more complicated.
This new arrangement is much simpler, and you can't see
the difference from the outside. |
