2 inch helical telescope focuser

thingiverse

Update: It's difficult to keep the eyepiece centered on the optical axis with this design. I doubt decreasing the drawtube width adjustablility will help (but printed draw-tubes work just fine!) I've been trying to think of a cool/easy way to keep it centered but I think I would rather just design a crayford style focuser.... I saw http://www.thingiverse.com/thing:13476 and realized it was built for 1.25" eyepieces. So I designed this from scratch to accept 2.0 to a little over 2.6 inch draw tubes, and not use metal bearings and be lighter overall. Doesn't really have the same aesthetic charm tho... let me know what you think about that! Mounting plate is .55" thick and mounts practically flush with 1/2" plywood. Not entirely sure that's the best idea now due to wanting some extra drawtube to back out for larger eyepieces, so the mounting may change. Also right now the mounting holes are where they need to be, something funky like 3+1/8" apart. The carbon fiber rod I used ended up to be pretty to really tight in the printed parts, but the plastic wheels still spin on the rod. not like a bearing, but they spin smoothly so I ended up with a very smooth helical operation! It's not perfect in that the drawtube can be aligned kinda off-center but it's not that bad/manageable as long as you use zip ties instead of rubber band. You may also wish to know that I'm designing this around a 10" F/4.485 with a 2.49" secondary mirror and a tube ID of 12" except it's a truss tube... so at the front of the scope, the 75% zone light cone has a diameter of 11.598" hence my concern with having a long enough drawtube. ehh, I'll see how it goes. Instructions Be sure to use abs juice because there isn't much surface area on these parts! You'll need a mounting plate, 3x "2inchPetal", 3x "2inchPetal LHT mirror". Also I'm using a 1.8 mm Carbon Fiber rod and pressing on some 23/32" rubber wheels I found at a rc hobby shop. I plan to either friction weld caps for the CF rod, or use some fuel hose and glue to captivate the rod. Using a 1.8mm drill bit, i drilled out the holes in the prints and drilled through the wheels. The CF rod is really snug in the printed parts, but the wheels spin with a little bit of force (each wheel turned out different tho). all in all, smooth operation! I'm using nylon bolts to attach the petals (size # 6 or 8, i forget) and #10 for attaching the mounting plate to the secondary cage of a truss tube telescope. once I'm done the stl's shouldn't need any manipulation, just print them in mm. Although... my printer is not extremely well calibrated... it is within 0.01" and the dimensions/clearances where chosen through trial and error, so good luck with that.