Any 3d printed mirror test stands out there?
Posted 05 May 2021 - 06:14 PM
Posted 14 May 2021 - 07:23 PM
Dale Eason did one for the Interferometry groups round robin test.
Ask Diego, he also belongs to the interferometry group.
Posted 14 May 2021 - 08:15 PM
A test stand can be designed for a specific mirror or made to accept any number of mirror sizes and thickness. The one I designed was for a specific mirror and made to take apart and be light enough to be shipped with the 6 inch mirror being tested by the group. So I have not responded until know since it was a special purpose stand. It had 2 point 90 deg apart edge support placed at the edge center of gravity of the mirror to help eliminate test stand induced astig. That was provided by 2 rubber o rings on spindles that projected from the back of the stand. I never published the plans. It was designed using Fusion360. I don't have any idea where the .stl file is anymore.
I would not try to make a 3D printed stand for anything larger than the 6 inch. I print a lot of things but that is not a best use of the printer for me. A wooden stand is quick an easy to build that can hold more weight in my opinion. For general purpose work I made an adjustable stand that can handle 6 to 18 inch mirrors of varying thickness from an aluminum plate with wooden feet.
Posted 14 May 2021 - 11:40 PM
Elaborate rear face supports tend to be somewhat pointless when the test system optical axis is horizontal or nearly so.
If the test system optical axis is vertical or nearly so a more elaborate rear support system is useful when testing large mirrors.
Since its possible to rotate the test mirror about the test system optic axis to allow (if the test mirror substrate is rotationally symmetric ) support system induced aberrations to be separated from test surface aberrations, the repeatability of of aberrations induced by the mirror support system can be more important than reducing such aberrations to a lower value.
A simple edge support using a pair of piano wire flexures can easily support the weight of a 20' diameter 35mm thick cylindrical glass substrate.
small diameter delrin pads also work well, printed plastic pads of the same diameter dont work as well.
Printing a plastic test stant for large mirrors is a time consuming and expensive task compared to using aluminium and plywood both of which which have a higher Young's modulus than plastics.
Posted 15 May 2021 - 07:11 PM
Even just setting them with 90* 3/4 plywood legs is fine, not what I’d normally do but this does help with the wide range of mirrors/sizes over a weekend. Didn’t affect the tests at all. One of the reasons Delmarva Mirror Making seminar was so successful at producing lots of very good Morris over a 3day weekend
- PrestonE likes this