Big Bertha 2.0: Something That I Didn't Think About

Big Bertha 2.0: Something That I Didn't Think About

It finally came time to mount Big Bertha 2.0 on the equatorial mount today--and I ran into a problem that I now realize is pretty significant. Deformation along the length of the telescope isn't a problem (especially now that I have switched the rail that the dovetail plate attaches to from 1/16" wall to 1/8" wall). But I hadn't considered the problem of deformation across the telescope. It was immediately apparent that when over at an angle, the primary mirror assembly would twist the rail quite severely.

I think the problem here is that all the stress of the primary mirror assembly is being transferred to the one rail to which the dovetail plate attaches. Within the existing design, I can see the following possible solution:

1. Add three more rails, so that I get a hexagon. This only adds about five more pounds to the telescope.

2. Add supports that transfer the load that is currently entirely on one rail (and at the bottom part of the rail alone, where most of the weight is) to distribute the load to the other five rails. This might be something as simple as using 1" square aluminum tube sections to connect all six rails together. This involves making a series of 60 degrees cuts (easy with the chop saw), then drilling and tapping holes that will allow them to lock to the rails going lengthwise. At least at the moment, I am having a little trouble figuring out exactly how this will work. The 1" square tubes are stiff enough, however, that I suspect that it would not take a lot of these segments to do the job. Remember that they don't have to be terribly strong themselves; they just need to stiff enough to transfer the load that is currently on one rail to the other five rails.

UPDATE: It occurs to me that the big problem isn't even twisting of the telescope itself--but that the lower assembly (which is very heavy, because of the mirror) is twisting on the rail because there is a single point of contact (round surface on a flat surface). Perhaps using an aluminum extrusion that consists of two right angles might work better. In that case, the round tubes drop into the extrusion. The tube then rests not only on a single point of contact, but also against the two uprights. In this case, a 4" wide base with two uprights would prevent the rotation across the flat surface.