Go fast, or go home! - Part III
- Ville Puoskari
- Aug 19
- 2 min read
One of the most frustrating challenges I faced with my telescope build was the secondary mirror spider assembly. The first version worked fine at home, but every time I transported the scope to an observation site, I had to deal with very minor collimation issues. The problem turned out to be subtle: the nuts and bolts holding the spider together each had the tiniest bit of play. Individually, it didn’t seem like much — we are talking about sub 0.1mm levels of play. But added together, it was enough to shift things out of alignment with enough bumpy roads traveled with the OTA in the back of my car. First attempt at solving it was simply tightening the whole assembly more securely to the tube. That worked temporarily, but it quickly became clear that I was just deforming the OTA itself and the whole assembly lost tension. Not exactly the perfect solution. The real fix was to machine a brand-new spider from a solid block of aluminum. This way, there would be no weak points, no unnecessary fasteners, and no flex.
Designing the part, preparing the work-holding, and machining the already greatly oversized block took over two days, but the result was completely worth it. This way I could save some money, as the block was a scrap piece I bought from a machine shop elsewhere for a bargain. The new spider is rock solid, fits the OTA perfectly snug, and holds collimation beautifully.
As a bonus, the aluminum stock I purchased was oversized, so I was able to machine a back-plate for the primary mirror out of the leftover material. This is mainly a cosmetic touch. Speaking of cosmetics - While I was at it, I gave the scope a fresh paint job and even milled a small aluminum finder shoe as a side project. These details might not affect optical performance, but they certainly add to the overall polish and satisfaction of the build.
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