Astronomy Hacks

Improve Dobsonian Motions with Milk Jug Washers

Eliminate the jerky azimuth motions that start to plague your scope after a while.

The azimuth (right and left) motions of inexpensive Dobs may be adequate when they are new, but often the azimuth motions become rough and heavy as the scope breaks in. This occurs because inexpensive Dobs use hard plastic or mechanical Teflon pads riding on a smooth laminate surface, and the friction and stiction (static friction) of this combination are difficult to control.

The real fix is to replace the bearings with virgin Teflon pads riding on bumpy Ebony Star laminate, but that requires spending money and devoting several hours’ work to the project. But there is a fast, free solution, albeit a temporary one. You can supplement the existing azimuth bearings by adding a center bearing made up of several thicknesses of plastic washers cut from flat-sided milk jugs. (Although milk-jug washers are traditional, some astronomers use old AOL CDs or even LP records; they’re called milk-jug washers regardless.)

The improvement in azimuth motions can be significant and, depending on the material you use for the washers, may last for dozens of observing sessions. When the washers begin to lose effect, it takes only a few minutes to remove the old washers and replace them with fresh ones.

To make the washers, cut full circles from the flat portion of the milk jug, or simply use recycled CDs. (In fact, a CD also makes an excellent template for cutting milk ...