Improved Rocker Box Pads

A small design detail in a dobsonian telescope is a method to restrain the mirror box in the center of the rocker box, to keep it from sliding side-to-side in the elevation bearings.

Rocker Box Pad
A standard carpet pad embedded into the wall of the rocker box
A common solution is to use a couple carpet pads to provide a lateral support that keeps the wood from rubbing. The pads do not add any friction that would keep the scope from tracking smoothly at high power. These pads are available in most hardware stores in both sheet form as well as pre-cut circles, usually one inch in diameter.

I have had trouble with these pads in Deep Violet. They do not stay put! Sometimes when inserting the heavy mirror box into the rocker I would catch a pad and simply shear it away from the wood. I ended up using a larger pad and using small wood screws to secure it instead of the adhesive.

While sanding another rocker box I had an idea to improve these pads. There is ample time to consider all the details of a design when spending a couple hours with a hand sander. The idea was simple, cut a simple pocket into which to insert the pad, leaving just enough of the pad above the surface to do the job. This would keep the pad in place as it cannot be hit from the side. This also allows a closer tolerance in the mirror box/rocker box fit.

Drilling a Pocket
Drilling a pocket to accommodate a carpet pad in the side of the rocker box
I used a 1″ forstner bit to drill a pocket about 1/2 the height of the pad. A forstner bit drills a neat pocket with a mostly flat bottom and nearly perfect sides with no breakouts. Care must be taken to achieve the correct depth on all the pockets. Setting the depth limit of drill press would be the ideal method to set the depth. Using a hand drill, consider a few wraps of tape on the drill bit or a mark with a permanent pen. Go slow and take care to drill a neat hole.

The result is a neatly recessed pad that will stay put!

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

2 thoughts on “Improved Rocker Box Pads”

    1. Depends on what you are sliding against. With finished wood I would recommend the carpet pads. Against fiberglass and resin? The teflon will probably work fine.

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