*
Monday 6th 42F, dark grey overcast with drizzle.
In the absence of any proper amateur astronomy to do, I had to fall back on ATM. So I started rebuilding the folded 7" OTA. The objective was an easy swap from long tube to folded front plate. I shan't bother with the quick release objective mounting bayonet plate. I hope I shan't be lifting the folded OTA unaided. So don't need the weight saving for dragging it outside as I did before.
The 3.5" Feather Touch needed a bit more elbow room on the backplate than the Vixen 2" base, but not very much. First I drilled a short chain of holes. Then ran the jigsaw around the marked circle. Much quicker than chain drilling the whole thing.
There followed some serious filing with a coarse, half-round file. Having built up a decent sweat and stripped down to my shorts [again] the adapter ring would finally go through the back plate. Now I just need to refit the back plate to the Porsa framework again.
Then refit the folding, flat mirror, T-shaped, collimation bars. I had expanded these in my original build to the maximum possible dimensions for fine adjustment and long lived collimation.
Job done. The plastic pots are to protect the folding mirrors when not in use. The back of the objective is protected too but this was removed for the photo. The folded OTA sits in a dead spot in the dome beside the stepladder handrail. I shall fix a batten to lift the objective well clear of the floor. There is a stumpy and also a full length dewshield waiting in the wings. Probably the stumpy one will do well enough to combat dew. I'll take some better pictures when I have the folded OTA mounted.
Then refit the folding, flat mirror, T-shaped, collimation bars. I had expanded these in my original build to the maximum possible dimensions for fine adjustment and long lived collimation.
Job done. The plastic pots are to protect the folding mirrors when not in use. The back of the objective is protected too but this was removed for the photo. The folded OTA sits in a dead spot in the dome beside the stepladder handrail. I shall fix a batten to lift the objective well clear of the floor. There is a stumpy and also a full length dewshield waiting in the wings. Probably the stumpy one will do well enough to combat dew. I'll take some better pictures when I have the folded OTA mounted.
Still cogitating on a quick release and re-fit "bar in a slot" bayonet system. For rapid, easy, secure and foolproof OTA swapping, on the big GEM. Something simple: A couple of aluminium, channel sections, laid on their sides and fixed across the saddle ends, top and bottom. Crossbars to fit the channels fixed onto each of the OTAs. Bars are stiffer than channel so ought to go on the OTAs.The mage shows how the pulley cords drop at about OTA mid-length. Hopefully this will ease loading and unloading the individual OTAs onto the mounting.
It needs some sort of locking pin or mechanism. Just in case any of the OTAs are inverted by accident. Or by the errant drives. A dovetail may offer the ability to balance the tube longitudinally by sliding. However I shall ensure balance of each OTA in a fixed position. Or with sliding weights on the saddle rather than on the OTAs. Which merely adds to the weight to be lifted. I had sliding weights on rails on the saddle before I removed them to fit three OTAs at the same time.
*
No comments:
Post a Comment