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One of the difficulties I face each time I make a new instrument tube is the necessity of making a suitable mandrel for laminating the composite material, usually carbon fibre/epoxy. My astrographs don't have adjustments for collimating the optics and that can only be achieved with very accurate tubes and housings for the optics. The same way that camera lenses are made.
I've been scratching my head for a while about how to make the mandrels for this baby until it suddenly dawned on me that I could perhaps 3D print them. I will need two of them - one for the actual OTA and one, almost as long, for the light baffle. The OTA being extremely short, has a large acceptance angle for stray light without a decent baffle.
I started with the less important one so that I can apply the knowledge gained to the second one.
The 3D printing took 4 days, with the printer running 17/24.
I used PLA because of its brittleness as this is a sacrificial mandrel that will have to be broken up and removed piece by piece when the carbon tube is finished.
After gluing all the pieces together, I skimmed the OD and the ends on the lathe, between centres.
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