What is Frankenscope? It is a scope that I can't resist tinkering with and experimenting upon. 
In this thread, the heart of the system will be a Tasco 60mm, f/15 (900mm focal length) refractor I found at a swap table at Scope Out 2015 (an annual event at the Cincinnati Observatory Center). Like the legendary monster, the scope and platform will probably turn out to be a mixture of inexpensive components from various manufacturers, married together by parts made out of wood and other materials from the hardware store. My pockets are NOT deep for yet another scope. This is a project for my education and entertainment. Already, I have stumbled upon a fun world of small aperture observing.
This OTA was made in China and is probably fairly modern, though I haven't tried to date its manufacture yet. It originally sold on a EQ-1 mount and has "From the Earth to the Moon" printed on tube at the sky end. I suspect that the objective might be pretty good, optically. It has a 1-1/4" focuser that, except for the pinion shaft and the bracket that holds it in place, is all plastic, even the chromed extension tube. I'm going to start with this.
I could, of course, try to scrounge a better quality metal focuser, but, I get that they are in short supply, especially for 1.25" EPs. OTOH, plastic is not inherently evil, especially when made thick enough for the task. The only physical load should be rigidly holding a diagonal, my largest EP, and, maybe a Shorty barlow. Besides, this focuser fits the OTA perfectly and has the correct Tasco tag on it already. It is just a little stiff to focus accurately.
I disassembled it and found a piece of fabric glued crookedly to the I.D. (inside diameter) of the focuser, opposite the pinion. This served as the 'bearing' for one tube to slide smoothly inside the other. In hind-sight, I should have left this in place to start this experiment and simply adjusted (backed off) the screws that mount and tension the pinion. Tuning these screws alone might have been all of the improvement required in the focuser motion. However, upon finding that viscous syrup (I hate this stuff!) that is invariably used to simulate "..precision, slow motion..", I plowed ahead and removed the fabric and the syrup.
What to use for a new bearing? The inspiration came right out of "Astronomy Hacks, Tips & Tools for Observing the Night Sky". Hack #42 suggests using the plastic of a common milk jug to create a stack of washers to improve Dobsonian motion. Could this plastic, if cut into narrow strips, be a suitable bearing for my focuser? I drank 3 glasses of milk just to find out.
First, I tried 2 quarter inch wide strips, spaced 120 degrees from the pinion. There was not enough clearance between the inner and outer tubes for this configuration. Then I tried a single strip a half inch wide placed directly opposite the pinion, like the original fabric was. This worked well. There was no angular backlash between the tubes and tension was adjustable with the screws that hold the pinion bracket in place. Next, I glued (silicon RTV is easy to remove if needed) the plastic strip to the ID so it doesn't move with the draw tube. Then I lubricated the rack and pinion with white lithium grease.
Does this focuser now have the buttery precision of a Crawford? Well, not quite, but it is very smooth. 
The focuser is molded plastic, after all, not machined aluminum with roller bearings. OTOH, I no longer bump back and forth endlessly past the ideal focus. With the tension lightly set, the focus knob turns with much less effort. There is a little lost motion in the focus knob due to the slots in the bracket being larger than the focus shaft. This is the reason the screws were originally so tight. I could make a new bracket, or 'V' the bottoms of the existing bracket. For now though, that very little bit of backlash is pretty easy to ignore.
Could I have tuned the focuser to my satisfaction without removing the original fabric bearing? I don't know. Had I been a little less rash, I could have explored this question better.
Everyone has probably heard the expression "You can't make a silk purse out of a sow's ear." The ATM's equivalent might be "You can't make a Unitron out of a department store scope". I don't doubt this. Due to other responsibilities, I will probably never be able to justify the expense, especially at today's prices, of the Unitron 145 (I do admit to a primal admiration for this scope). On the other hand, with some tuning, reasoned modifications and upgraded finder and EPs, I might be able to scratch my Unitron itch, at least partially, without investing thousands. I do intend to have fun with the project.
Edited by Tenacious, 23 October 2015 - 11:29 PM.
I'm always the last to stumble upon issues of social etiquette, just ask my wife!
