Rapid OTA mounting continued.

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Thursday 39-48F: This morning I removed the 6" + 90mm refractors simultaneously from the saddle. It was completely effortless thanks to the pulley system.

Bolting the new channel section on its side, to the saddle, presented a slight problem. Any through bolts would impede the square tuning from entering the channel. Any bolts used to hold only the lower leg of the channel to the saddle would have to be countersunk. Not an easy task when access is blocked by the upper channel leg. 30mm long bolts won't allow themselves to be tilted in a 20mm high channel.

However, provided I allow the square tube to be slotted to half way I can use long bolts right through the channel and saddle. The bolt shanks then become the lateral location devices. Downside is the weakening of the rather small section of the crossbar tubing I intend to use on the folded OTA. I could stuff the tube with solid aluminium before slotting. Or go up in size of channel and square tubing to retain the necessary stiffness and strength.

Not that loads on the crossbars are particularly high. Say ~40lbs/2. The loads would also be at right angles to the slots. The tube would be closely housed in the unbroken channel area for well beyond the slotted section. The tubes are fixed at their outer edges of the folded OTA. Once the OTA is mounted, the lower saddle screw will be tightened to lock the OTA solidly in place.

Perhaps I am simply worrying too much? It's just that I usually like to have a decent safety margin to avoid the risk of expensive accidents. I'll have another look in the scrap aluminium pile for a sturdier match of channel and tube. In the end I decided to use the original, Birch plywood, cross bars for the first trial. I just need to drill a single hole to fix the channel to the saddle and I can test the new folded OTA mounting system. It rained steadily all day! With the folded OTA upstairs in the dome and the work going on downstairs in the shed/workshop, there was a lot of to-ing and fro-ing.

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