Building a 24 inch telescope

Rocker & base

The optical assembly must be properly supported for all its weight and has to be manupilated with ease and in a fluid manner. This is the duty of the “rocker” in dobsonian vocabulary.

Rocker

The rocker box features a significant use of wood and is made from 15mm plywood, screwed and glued together, then coated with three layers of marine varnish. It consists of two semicircular altimute axes (450mm radius and 30mm thick), resting on a plywood frame via four aluminum supports and eight 10x19x5mm ball bearings. The motion is very smooth without being uncontrollable. Brake pads will be added later to adjust friction. The semicircles are attached to the primary frame using turned aluminum sleeves, ensuring the wood is neither compressed nor in contact with the screw threads. The bearing strips are currently made from kitchen counter edges, to be replaced with metal strips in the future. A spacer is added to reinforce the rocker, ensuring proper squaring and rigidity so that everything slides smoothly on its rails.

Base

The base supports the entire telescope and is mounted on pneumatic wheels. It allows for azimuth rotation. The foundation consists of a welded steel frame on the wheel axles (20mm diameter), enclosed with two large 15mm plywood panels and beech spacers. The rigidity is excellent. A 10cm-wide polystyrene bearing strip is placed on this base. Then, a second platform rotates around an 8mm threaded axis on brass bushings. It is supported by eight 19x10mm ball bearings, asymmetrically positioned to align under the rocker’s bearings. This ensures the weight transmission is as vertical as possible, avoiding flexing. In the end, the azimuth motion is excellent, and only a brake pad is missing. The rotating base is large enough to accommodate future equipment, such as batteries for motorization or secondary mirror heating, and of course, electronics for a pointing system (like Argo Navis, for example).