No project is ever completely done, even one “finished” decades ago… My 6″ f/5 RFT is the current incarnation of my first telescope, Primero. Built into an 8″ irrigation pipe this ‘scope is a rich field ‘scope that is just fun to use. And yes, I worked on this telescope again.
One feature I have always meant to change is the tube rings. Simple aluminum straps that I kept loose enough to allow the ‘scope to be rotated to keep the eyepiece at a convenient angle for viewing. The issue is that in use the tube would constantly slide down through the rings throwing the mount off-balance.
I finally got around to fixing that. A set of 3D printed rings along with a stop mounted to the tube that prevented this sliding, keeping everything centered and balanced. The rings are attached to each other by the two dovetails and a handle forming a cage.
The smooth aluminum tube rotates on felt pads kept just tight enough to provide some friction to the rotation. A pair of stops with bearings mounted to both ends keeps the optical tube from sliding through the rings. As the new rings also include a nice carry handle the telescope is much easier to move around and hold while attaching to the mount.
In order to fit around an 8″ tube these rings are just under 10″ outside diameter, any larger and they would not fit on the build plate of the 3D printer. Actually, telescope parts for 6″ or 8″ telescopes is the main reason I have always purchased 10″ build volume printers.
A few tricks allow the 3D prints to be quite strong… All the brass heat-set insets are set from inside the rings, they cannot be pulled out without pulling them through the ring. In addition the rings are modeled with extensive ribbing rather than infill, this provides multiple thick printed walls rather than the relatively weak infill to support the load.
I did print a Vixen style dovetail bar for the rings, but it proved to be far too flexible, the scope would jiggle and bounce. I took it off and put a machined aluminum dovetail on. The second dovetail is the original hand machined Losmandy style dovetail bar.
At the same time I removed the old Telrad base from the ‘scope, spending time cleaning the original foam tape off the aluminum tube. It was replaced with a 3D printed Vixen style finder mount, with an adapter/riser to allow use of the Telrad, or to allow use of the PiFinder or one of my optical finders.
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