June 15, 2022
Description
A mirror cell for a six-inch Newtonian. It may be rescaled or adapted to metric - the user just needs to identify which hex-bolts will fit after scaling. Note the depicted backplate is not included, it needs serious revision to be tenable. That's from a shelved design for which I made one wobbly but working prototype. But the cell itself is perfect for the job!
If you do plan on re-scaling, you can find CAD files for any and all screws on McMaster-Carr's site.
Print directions
This part will hold a two-to-five pound hunk of glass. It needs to be sturdy. 3-5 perimeters depending on your nozzle size, and a cubic infill of 30% to 50% depending on how brave you're feeling. The rest can be printed solid.
Bill of Materials as Scaled:
Assembly
Use the primary cell as a marking/drilling guide for your back-plate, ideally plywood.
Pull the 3 large bolts through the cell so the hexes embed. This may need some force or heat-setting. Then run a washer, spring, and washer over the bolts. Hold the cell face-down now, with the springs upwards. Pull the back-plate down over the bolts, and secure it with the three knobs. This may be challenging - it took a bit of elbow grease for me to put the anti-vibration knobs on, but it was worth it. The telescope maintains collimation perfectly.
The washers are optional, but help tremendously to reduce long-term creep in this print. I'm not sure how big an issue that is or isn't, because my prototype uses them!
Flip it back, insert the three feet into the slots. Then gently place the primary in. Take extreme care from here on to not touch the primary with the screws. The coating is very fragile.
Hex nuts go inside the clips, bolts through those. Nuts also through the underside of the cell. You may need a heat tool to insert the nuts from underneath. You may forgo the nuts in the clips, if desired.
The clips should be only tight enough to retain the mirror - you should be able to slide a piece of paper between them and the mirror / freely spin the mirror. The same goes for the side-bolts, which should just keep the mirror from bouncing around.
You now have a sturdy, collimate-able primary cell for a six inch newtonian.
See below for details on the assembled cell.
What if I use metric/ can't find imperial screws or vice versa?
Metric or whatever standard works fine - this is thread agnostic, we only care about clearance and the width of a hex-nut. Print a little section of this (your slicer should let you do this!), go to a hardware store, find what screws/nuts fit.
Can you provide the backplate?
The backplate would take some revision to be workable. If enough support rolls in from Hadley, I can support my other projects some more. But for now, this is as-is - and this plus my focuser is already enough to make building a larger newtonian significantly easier.
Does this scale up or down?
Yes, but so do the screw-holes and engineering challenges. Also note that beyond eight to ten inches, mirror support becomes much more complicated. The square-cube law also comes into play, and I doubt even a monolithic print such as this would adequately hold up.
Modifications, etc:
You can find other telescope parts, improvements, alternates in my collection here. Support these files as well!
How can I support this?
Tips are always appreciated, as is support on Printables. I'm also (barely) on Patreon, where I host shelved projects I don't have time to provide support/documentation. Designing, testing and improving takes a lot of time, parts, and filament - and support gets me more of all three.
License:
Creative Commons — Attribution — Share Alike
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