Orion Astrograph 8" f/3.9 focuser for NEMA 17
Description
Focuser for Orion Astrograph 8" f/3.9 telescope OTA (Optical Tube Assembly), should fit others using a similar 2" Crayford focuser. It could be installed the other way, but I wanted to maintain the use of the dual speed Crayford for manual use. (Might help with AP, but the stepper should be good enough, and I could use different pulleys if needed.) I also didn't want to have it next to the focuser as most designs seem to use, because I already find I don't have a ton of room if I need to spin the tube for visual use. Required materials: Longer M3 screws (6 if you transfer 4 of the original ones to the motor or 10 if you don't) for thickness 4mm: M3x15 4mm bore GT2 pulley (20 tooth) 5mm bore GT2 pulley (20 tooth) GT2-110 belt NEMA 17 stepper motor Controllers that should work: 1. OnStep controller: https://onstep.groups.io/g/main/wiki/home (Highly recommended, works with Smartphones, INDI (Linux/Mac/Pi) and ASCOM (Windows) and can have a SHC (Smart Hand controller) which will let you control the focuser, and of course, provide goto control for the whole telescope.) 2. OnFocus controller: http://www.stellarjourney.com/index.php?r=site/software_focuser (Focuser only: Works with ASCOM/INDI, no smartphone or SHC) 3. RomanHujer's Focuser Hand Controller (FHC): https://www.thingiverse.com/thing:3384824 (Focuser only) 4. Anything else capable of controlling a stepper motor. Tools: Allan Wrenches 3D Printer Suggested installation: Optional: Print the test plate to check fit. (I think it has 3mm holes everywhere so the 5mm lock won't fit, it's just to check that things are centered.) 1. Remove the focuser (Drawtube will be lose after so keep that in mind.) with the 4 outer screws. This will cause the black part along with the knobs to come loose. 2. Remove the single knob. (There's a small hole to get an Allen wrench through to losen the set screw.) 3. Attach 4mm GT2 pulley where the knob was removed. 4. Remove the lock knob. 5. Remove the two screws holding the shaft tensioner. 6. Install with the triangle facing up. 7. Replace the two screws holding the shaft tensioner. (Inner 2 M3 screws) 8. Attach 5mm GT2 pulley to Stepper motor 9. Put belt around the shaft pulley, and slide motor in, looping belt around it. 10. Screw motor in place with M3 Screws. (I used 4 of the original ones.) 11. The belt should be tight, and it should be assembled. (The print provides a bit of tension on it. If left in a hot car or similar it might deform easier than a normal print, so be warned.) 12. Install back on OTA with the 4 outer screws. Making sure that the drawtube is aligned flat with the shaft. 13. If needed adjust tension via the middle screw. 14. Install lock screw and check that it functions. 15. Connect to controller/camera setup and GO! Notes: A. It does not have a safety switch or anything, but due to the design of the focuser, it shouldn't be able to move outside the range. (But if it does, you've been warned and I'm not responsible as in general.) B. It does rest lightly against the secondary fin adjustment on mine, I do not see how that will be problematic, but be aware of it. I'll update this if I find any issues with it. C. The artifact in the OpenSCAD view doesn't happen when compiled. It's is due to the annoyingness where sometimes subtracting things will leave an artifact in the preview view (F5). So if you download it and see that, you can ignore it as long as it goes away when you Compile (F6) as it should.
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