The Formica-Teflon Cross - An alternative mirror edge support for Dobsonians

[Roel]

While designing a ultra portable travel dobsonian I encountered the problem of applying a sufficient primary mirror edge support within the extremely limited amount of space available. I wanted something as simple as possible, which would always support the mirror in the center of gravity. I came up with the following solution:

First I determined the center of gravity with this great online tool: http://www.cruxis.co...ecalculator.htm

I glued two narrow strips of Formica onto the edge of the mirror, exactly in its center of gravity. The center of both strips were placed 90 degrees apart.

Next I glued two vertical strips of Teflon directly onto the inside of the primary mirror box:

And this is what it looks like with the mirror installed:

The mirror is now supported only at the point were the Teflon and Formica meet. Because the strip of Formica is placed at the COG and the Telfon strips are 90 degrees apart, the mirror is always supported correctly, even when sliding up and down during collimation. The required space is even less than with a cable sling.

I have used this idea on several telescopes now and it works great! The fricton between the two materials is very low without "stiction" so collimating is very smooth, even with the OTA pointed relatively low.

By the way, this is the complete telescope, a 350mm (14") f/4:

 

[faulksy]

lovely idea, but they say teflon can cold flow, acetal is best and causes the least stiction. might be ok with a light mirror though

[mapstar]

Nice job Roel. It does as Mike says cold flow but it will depend how the mirror is stored. I suspect horizontal in which case it shouldn't be a problem.