I pondered over the design of the cradle for a long time and had quite a few goes before the final one.
Basically it is made from double layer 12mm ply giving 24mm thick rings top and bottom.
- My OTA has an outside diameter of 230mm so I routed an inner circle of 234mm diameter to allow for the felt insert between the cracle and the OTA.
- I started with a square "ring" then took the corners off as I could imagine how often I would hit my knuckles on them. There is no reason they could not be left square on the outside, I happen to like the octagonal look.
- The minimum thickness for the rings is 25mm at the sides. This was to give adequate strength and room for the side boards to be attached and away from the OTA.
- The side boards are simply 12mm plywood 150mm wide and 180mm high. They were glued and screwed flush with the outer surfaces of the rings.
- When the rings were glued to the side boards I ripped the whole setup down the middle with a fine saw giving the two halves.
- The two halves were hinged together on one side and the clasps used are simply the suitcase ones available form most hardware stores.
- I lined the inside of the rings with self adhesive felt to prevent too much damage to the OTA.
- This clamped very well and needed no other adjustments.
- The bearings were made out of 12mm ply doubled to give 24mm.
- They were made as one unit with a 12" diameter, I worked on the generalisation that the bearing should be 1.5x the diameter of your primary.
- The cutouts are just for decoration as were done with a hole saw.
- The circle was cut in half with a fiine saw.
- The bearing surfaces were finished with some rough finish laminate I "aquired" from a friend. The ends are secured with heavy duty staples.
- The bearings were mounted with some knock down furniture fittings. When I get to the split ring mount they will be replaced with T nuts and large knobbed bolts for a simple tool free change.
Enough for now.
Cheers