This video demonstrates the detailed process of machining with a mill the spider vanes (secondary holder) of a VIXEN VISAC VC200L Telescope.
After carefully centring the spider vanes on the milling table, the procedure is straightforward if done with care and produces excellent results.
Read on for more astronomical information 🙂
The Vixen VC200L telescope features VISAC (Vixen Sixth-Order Aspheric Cassegrain) optical system which is free of coma, field curvature, spherical and chromatic aberration.
The telescope has an enviable reputation for its flat field for astrophotography, producing exceptionally sharp images with no chromatic aberration due to the VISAC design.
The most significant complaint people have about the Vixen VC200L is the thickness of the spider vanes. They are 6mm thick, probably to achieve good results in the casting aluminium process.
This leads to, fat rhomboid – square core for brighter stars instead of the actual – desired centre/rounded. At 2mm, the vanes are still very strong, and no detrimental effect can be seen regards to holding the secondary mirror in place, being still solid as a rock at 2mm thickness.
The obstruction of the 6mm spider vanes is also significantly more in astronomical terms. By milling out 71mm(length) X 4mm(width) X sides, we are gaining back 1136sq/mm, which is roughly the size of the secondary mirror!
We are counting photons with these instruments, after all, so every bit of light/aperture helps 😛
Milling a large radius on a milling machine does not have to be limited by the size of the rotary table.
When tilting the head of the mill with a large cutter, be it a boring bar, fly cutter etc, the resulting cut is an ellipsis. This technique has been used for a long time by machinists before PC’s, CNC’s and other technological aids made their appearance in the industry.
The problem (or not 🙂 depending on the specifications tolerances) with the existing literature (such as the Machinery’s Handbook and others) is that the formula being used assumes that the desired width of said large radius is 0!
The following calculator averages the angle required to accommodate the width as well to provide a better approximation. By using the following calculator you can approximate a true circle radius with an accuracy of few microns.
Astronomy is a really broad subject. Same goes for astrophotography and all the weird gimmicks of this hobby.
Because for the most part of the year, I went full berserk mode into both and have gathered allot of images, data, procedures and various tutorials, which would kind of hijack this personal blog I decided to move astronomy and astrophotography into its own separate – special website 🙂
So if you are into any of those things or maybe like “nice” images of the cosmos, do visit the website : http://www.starcanvas.org
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