Focuser Updates

Updates have been made to the focuser based on the 3d prints. One unexpected change is the possibility of doing away with the bearing axles entirely. I placed the bearings in their slots on the drive block print, and even with tight tolerances they spin very freely when placed directly against the Onyx surface. I guess use will determine the overall experience. Will its slightly pebbled surface prove too bumpy? Will I have to at least sand the draw tube? Will a little car wax go a long way? Will the bearings shift too much to hold precise focus?

Time will tell, but for now I am excited about the idea of removing the bearing shafts entirely because of the aforementioned difficulty in mounting the bearings on the shafts. Turns out the home refrigerator was insufficiently cold to do the trick. I was about to bring the toaster oven into the mix by refrigerating the shafts and toasting the bearings… or try using dry ice to freeze the shafts down to -80C. For now, the plan has changed to shaftless bearings because if it works, why bother with more parts and assembly.

It makes me wonder whether I should go through the trouble of printing the focuser separately from the tertiary housing so I can hot swap focuser concepts. It would also make assembling/adjusting the drive plate significantly easier. Up to this point the focuser drive block has been separate just for ease of unit testing. Maybe this will help in reality.

At first, I placed the bosses for the eyepiece retention screws in the wrong places. (Yes, I’m using screws not compression rings. Research suggests compression rings still apply pressure unevenly, and the nylon thumbscrews I’m using don’t mar the eyepiece barrels, to satisfy those who care. Personally, I don’t care at all about marring the eyepiece barrels since good tools are made to be used, but the nylon screws also cut down on weight.) Upon mirroring the tertiary housing to the left side and checking everything, I noticed the screw placement was overlapping. So I rotated them 45 degrees and now they actually will be better positioned relative to gravity.

In turn, the placement of these little screws will change the shape of the outer shell that holds the whole scope together (technically the mirror box that is extended so the retractable secondary cage can fit inside). Interesting that such a small detail can affect the dimensions of a much larger part. Here you see the focuser in black and the screws in a shiny silver even though they will be off-white nylon in reality.

Has every aspect of the tertiary module been designed? For now, it appears so. I added the holes for attaching to the rotating secondary cage. The focuser is updated, the filter cartridges are ready for their first print run, the tertiary mount is ready for unit testing. I am going to hollow out the back because there is a lot of solid material back there for no reason.

Oh, also the cover for the secondary cage attachment holes. Who’d have thought after a 20 hear hiatus on 3D modeling I’d be building complicated and real things in 3D.

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