Orion Astrograph 8" f/3.9 focuser for NEMA 17

thingiverse

Focuser for Orion Astrograph 8" f/3.9 telescope OTA, suitable for other models with a similar 2" Crayford focuser. It's installed to maintain the use of the dual-speed Crayford for manual operation. This could be reversed, but I preferred to keep it as is to ensure smooth AP performance and allow for different pulleys if needed. Additionally, I wanted to avoid placing it next to the focuser, as most designs do, because I already find myself with limited space when spinning the tube for visual use. Required materials: Longer M3 screws (6 or 10) for a thickness of 4mm: M3x15 4mm bore GT2 pulley (20 tooth) 5mm bore GT2 pulley (20 tooth) GT2-110 belt NEMA 17 stepper motor Compatible controllers include: 1. OnStep controller: https://onstep.groups.io/g/main/wiki/home (Recommended, works with Smartphones, INDI, and ASCOM) 2. OnFocus controller: http://www.stellarjourney.com/index.php?r=site/software_focuser (Works with ASCOM/INDI only) 3. RomanHujer's Focuser Hand Controller (FHC): https://www.thingiverse.com/thing:3384824 (Focuser only) 4. Any other device capable of controlling a stepper motor. Tools: Allan Wrenches 3D Printer Suggested installation: 1. Print the test plate to check fit, if desired. 2. Remove the focuser with its 4 outer screws. Note that this will leave the drawtube loose. 3. Remove the single knob by inserting an Allen wrench into the small hole and loosening the set screw. 4. Attach a 4mm GT2 pulley where the knob was removed. 5. Remove the lock knob. 6. Remove the two screws holding the shaft tensioner. 7. Install the motor with the triangle facing up. 8. Replace the two screws holding the shaft tensioner (inner M3 screws). 9. Attach a 5mm GT2 pulley to the stepper motor. 10. Place the belt around the shaft pulley, then slide the motor in and loop it around itself. 11. Secure the motor with M3 screws (using 4 original ones if desired). 12. Tighten the belt and assemble the focuser. 13. Install the focuser back onto the OTA using the 4 outer screws, ensuring the drawtube is aligned flat with the shaft. 14. If necessary, adjust tension via the middle screw. 15. Install the lock screw and test its function. 16. Connect to a controller or camera setup and begin operation. Notes: A. There's no safety switch, but the focuser design prevents it from moving outside its range. However, be aware of this limitation. B. The focuser rests lightly against the secondary fin adjustment on some models; this shouldn't cause issues, but monitor for potential problems. C. An artifact may appear in the OpenSCAD view due to subtractive modeling issues, but it disappears when compiled.