Dome build: Wheels and lifting octagon braces.

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Friday: Dull and grey but dry. I centered the dome base ring and then marked the 2x8s ready for fixing the wheels.

There will be a conflict in the wheel's coach screws overlapping the posts.

There was no obvious way to have the wheels situated over the posts. The logical answer is to fix all the wheel trucks a few inches anticlockwise of the posts. The wheels can then be bolted straight through the 2x8s without any problem. I have drawn arcs on the 2x8s as a guide to wheel placement using the base ring as a stencil. The lines can also be used to guide a jigsaw to curve the 2x8s.

By lunch time I had all eight wheels bolted to the 2x8s a couple of inches away from the nearest octagon posts. I inverted the 10mm coach screws to put the domed heads down, threads upwards.

A tap upwards with a hammer on the 2x6s and a Bessey F-clamp was enough to indent the bolt heads into the cross braces. So that the 2x6s fitted tightly underneath the 2x8s for extra support. It looks much neater too than in their original, lower position.

The observant will notice I've left the octagon wall wide open above the [stowed] observatory ladder. I have plans for a pair of hinged doors to allow easy access to the veranda between the ladder handrails.  The ladder has been tilted almost upright to make more room for the dome components stored 'downstairs' out of the inclement weather.

The octagon cross braces were never intended to be visible. Being hidden [eventually] by the plywood cladding. Having the braces at the top of the posts will also provide a better fixing for the ply walls. A lower cross brace near floor level will provide further support for the plywood, observatory walls. I'll probably leave the middle braces in place to stop wall flexure in gales. Though I don't want to clad the building until I am satisfied I don't need easy access though the framework for the building work.


Saturday: I found a pair of cheap inline skate boots and bought them just for the wheels. I had to grovel on the ground outside with my cycle tool to remove the wheels because I had no room, nor use for the boots. The vendor had no need of the boots either so they were discarded.

I think I shall add alloy angle brackets to the main wheel axles to carry the skate wheels for centering the dome. This should make a neat and compact arrangement without the need for very tall "stalks" on the 2x8 base ring.

I may remove the bearings [temporarily] and turn the wheels down in the lathe to make them even more compact. Or I could use an angle grinder with the disk working across the tyre to remove rubber without the bearings over-revving. That might lead to eccentricity unless I resort to turning the last bit of tread down to size.

Later I applied poly. freezer bags to the naked support wheels to protect the needle bearings from rain and possible rust. The bearings are already greased but there is no point in taking risks before they enjoy the protection of the dome.

Sunday: I spent the night [repetitively] dreaming of ways of fixing the centering wheels to the main dome support/rotation wheels. I have some 2"x4"channel which could be cut into strips on the miter saw. Sadly the 2" webs aren't quite wide enough to allow the skate wheel axles to fit. I'd hate to have to add another plate on top because it adds to the complexity and would look rather crude. I have some 3x3 angle profile but that isn't deep enough to reach the main wheel axle. Ideally it needs to be a 3" wide by 5" tall, L-shape. Perhaps I'd better go back to looking at roofing steelwork for a centering wheel support?

I came up with umpteen ways of retaining the dome from lifting in a storm. Favourite are disks on top of the centering wheels to catch the base ring. The vertical ribs might need a small slot to clear these retention disks to avoid blocking dome rotation.

Click on any image for an enlargement.

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