Circular Arcs
The circular arcs on the skyStopper are made of 13 layer baltic birch plywood.
They roll on double bearings, and the weight per bearing is small.
The construction of the SkyStopper begins with the computations for the required arc radius. Actually there is a range of allowed radii. During construction, the actual achieved radius is measured with precision, and the math for the rest of the unit is adjusted to account for the actual arc.
The arcs come out right thanks to the use of a precise adjustable pivoting routing jig. The jig makes it easy to get an arc with a straight edge on one side and a measured radius on the other side, well machined and smooth.
As a hobbyist myself, I know how attached I get to some of the gadgets I have designed. I would not consider replacing them while a repair or adjustment is still an option.
You might have a platform which you made yourself, but you might want a better arc for it. You can special order an pair of arcs of the right size from me, for a nominal fee, and I will ship them to you. A pair of custom made arcs of the proper width within 1 mm of the requested radius can be purchased for $99 plus shipping. Tighter tolerances are possible.
To specify, you need to note the required overall radius and the thickness of the arc strip at the center. The material will be a piece of selected flat 13 layer baltic birch plywood, 17.3 to 18.5 mm thick.