INTRO
I recently printed a Bhatinov mask for my newly acquired 10" Dobsonian telescope and needed a way to easily and securely attach it. Printing a mounting ring in it's entirety was out of the question since the bed of my printer wasn't big enough. So, I decided to print sections of the ring and glue them together. Knowing I would probably need rings for different filters (I also bought a premounted solar filter), I wrote a script for openSCAD so I could easily control different variables.
PREP
1) Download and install openSCAD
2) Download and save all of the files
3) Open openSCAD and then load the FilterRingSectonRevx.scad script
4) Get a ruler with a metric scale and/or some calipers
5) Gather your filters and your scope and do the following
DESIGN
First review the diagram that shows all of the pertinent dimensions in millimeters you will need to know and use in the program:
*OD (Telescope Outside Diameter) - carefully measure this and add 1mm*
*FilterOD (Filter Outside Diameter) - again, measure this and add 1mm*
*height - this is the distance between top edge of scope to bottom edge of the collar*
*FilterThickness - measure this with calipers if you have them*
*overlap - the distance between the edge of the filter assembly and the actual filter material*
*SectionCount - determine how many ring sections you need to print based on your scope OD and the size of your print bed. For a smaller scope this value can be set to 1. For my Apertura 10" DOB I set this to 3 for three 120 degree sections*
*AddClips - when set to "true" this variable instructs the program to add a small retention clip to each section. For some filters you may want to set this to "false" and have a friction fit. I would recommend setting this to "true" for extra security*
*ClipDepth - sets the depth of the clip relative to the OD*
*ClipCount - if SectionCount=1, this variable tells the program how many retention clips to place on the filter ring. It defaults to one per section otherwise.*
*AddSupport - if set to "true," adds a small block to an area of the model that will require support on the print bed. This allows you to disable supports on your printer and provides a cleaner mating surface*
Once you have plugged in all of your values, do a quick render and look at the result. Make adjustments as required (use my screen grab as an example) and save as an STL file
PRINT
1) Load the STL file into your slicer and flip it over so the retention clips are on the top. You may also have to move it in X and Y rotate it around the Z axis so it fits on the bed. Enable supports if you chose not to add them to the model in the previous step.
2) Use the settings below for your print. Let it cool after printing and do a fit check on both the filter and the telescope. If it it looks good, print the remaining sections. Otherwise, adjust and repeat.
ASSEMBLY
1) Clean off any remaining support material
2) Arrange sections on a clean flat surface
3) Apply glue to the inside of the thin tabs on the end. Gorilla Glue works well for me.
4) Squeeze in the mating tab from the adjacent section and use paper clips (see image) to hold both surfaces in place
5) Repeat for remaining sections
6) Let the glue cure for at least 12 hours
7) Do a final fit check
8) Glue in your filter or mask
wallyware
