Dome build: Dome steering wheels. Pt.1.

Sunday: I spent last night [repetitively] dreaming of ways of fixing the centering wheels to the main dome support/rotation wheels. Without horizontal centering wheels or rollers the dome would have no 'steering' and would just roll off the building sideways at random. The centering wheels keep the main support wheels firmly on track by running along the inside of the dome's base ring. The curvature of the main wheel's contact surface avoids tyre scrub on the endless corners.

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 easily. I'd hate to have to add another plate on top because it adds to the complexity and would look rather clumsy.

I also 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?

Here is the first attempt for measurement:

A short length of base ring has 

been added for the image.

I cut a 40mm wide strip from the 2" x 4" channel section. Then sawed off one web by hand. The initial, main axle hole was too high so I filed it longer to allow the bracket to sink below the track's bottom edge.

The main wheel tracks rather near the inside of the base ring. So the skate wheel could be moved nearer the edge of the alloy top section by a few mm. [1/8"] I could also turn down the diameter of the wheel by as much as 20mm if necessary. That would move the track nearer the center of the base ring.

The angle profile isn't really tall enough. Nor the web wide enough. Perhaps I can find some simple shelf brackets as donor material to do the job properly. There are dozens of potential shelf bracket donors at a big DIY outlet in the city. I intended to visit the outlet to see what would best suit my needs. Since the brackets come in assorted lengths I imagine they must be stronger/wider in the larger sizes. Since there will be waste material cut from the top, shorter leg this can be used to reinforce the upright leg around and above the main wheel axle hole.

I have came up with umpteen ways of stopping the dome from lifting in a storm. My favourite, so far, is having alloy disks on top of the centering/steering wheels to catch the base ring if it lifts. The dome's vertical, plywood ribs might need a small slot to clear these retention disks to avoid blocking dome rotation.

Always one to listen to sensible advice, particularly from experts, I have ordered some normal skateboard wheels online. Luckily, plain white is right at the budget end of the market. The 45mm width and smaller diameter [60mm] are both in favour of greater success. I shan't need so much inward offset for the wheels to get the base ring back on track. Though the difference in radius is barely 8mm it all helps the cause.

The height of the wheel, when turned to horizontal, means reduced cantilevered loads beyond the main wheel's axle hole. The wider wheels will allow much greater variations in dome ring height due to wind, wobble or warping.

My 42 mile cycle ride resulted in eight, stainless steel, shelf brackets. With excellent depth and form for strength at the bend, and rust free into the bargain, I was delighted to find them at quite a modest price. They should be amply stiff enough in use with a 50kg, 110lb load capacity. The 40mm width is absolutely perfect for self-centering and alignment in the pressed steel fork of the main wheel housing.

The image [right] shows the shelf bracket in place with the skate wheel attached. I marked the center of the track to ensure it lay over the center of the 'crowned' main wheel.

It is hard to believe how well the bracket fits its role to such perfection. I added a small bolt to retain the lower leg when the main axle bolt wanted to alter the angle of the bracket as the large Nyloc nut was tightened.

The wheel's colour match is as close as could be desired and both will hopefully show up as dome perimeter landmarks in the dark. The shorter leg of the bracket will need to be removed to avoid sharp obstacles projecting in the dark. In fact the bracket can be cut off within the radius of the small wheel for safety.

Needless to say, I am delighted with how well the bracket and its wheel turned out. I may turn off the dished outer rim of the skateboard cruiser wheels in the lathe. It serves no useful purpose and there is ample tread width without it. I may use some 8mm stainless steel, threaded rod [studding] for fixing the centering/steering wheel. Spacers are needed to lift the wheel clear of the racket. This function can best be fulfilled by an adjustable Nyloc nut. Or even a pair of normal nuts locked together.

Whoops! I have just been reminded to leave some wheel clearance for non-circularity of the dome base ring. It had completely slipped my mind!

Wednesday: Completed drilling and fitting the shelf brackets to the main wheel pressings. No bolts to fix the wheels. Another shopping trip! Bought all stainless steel screws and nuts for the wheels and brackets. Should have finished the wheels by tomorrow lunchtime.

Click on any image for an enlargement.

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