From wpk@saao.ac.za Wed Mar 14 09:23:17 2001 Date: Wed, 14 Mar 2001 09:12:17 +0200 (SAST) From: Willie Koorts To: Mal J MacDonald Subject: Re: Wow, you did a great job. On Tue, 13 Mar 2001, Mal J MacDonald wrote: > I just picked up your web page on the 9 inch split ring, I can't believe > the work that went into making the scope and web work. > Some of your ideas I'm gona use is: > 1, Holding the Truss tubes in place. > 2, wing-nut inside the driven roller-skate wheel. > 3, Somemore, somemore, somemore. > > The scope I' working on will be a 12.5 inch F7 (I hope). It's a standard > 2 1/4 inch thick Pyrex. In place of the split ring, I'm edging into a > light weight type (sort of a Dob). The Mirror support will be three > triangles, like yours, but the three mounting screws will be my > collimating adjustments. I may use your idea on the sled focussor > because it also solves the distant measurement between the primary and > secondary mirrors. > > I've a lot of thinking to do because I've finished grinding and will > start to polish when I finish my new Honey-DO list. > > Oh ya, the R.A circle will be a 4 foot measuring tape glued on the edge > of a flat of some type. This gives about 1/2 hour for 1 inch, or about 1 > arc second for each 1/32 inch. So M22 R.A = 18h 36.4 m or about 37 > 3/16 inches. I needed a clutch to lock/unlock the ring, bet I could use > the wing nut on the skate wheel Idea. > > Thank you for the world of great ideas. > Mal > > Mal MacDonald, USA, 42.2078 -70.8188 (more-or-less) Hi Mal Thanks for the nice comments - glad you could find some useful info from my efforts. It sounds a lot like what I did when planning my scope - I looked around at what others did and combined their good ideas and added some of my own to end up with a system that is to my liking. "My" method of holding the truss-tubes have been tried by a few others, quite successfully already - I quite like it and its still gripping like crazy after all this time. I half forgot about the wing-nut in the roller-skate wheel since it works so well - after setting it up initially, I never touched it again after that. The amount of frictional resistance just seems to stay the same over time. I set it such that one can slew the scope with some effort but there is no slippage when driving by stepper motor. It just makes a squeaking noise when pushed but this actually seems to impress people and warns me when the kids are starting to fool around if my attention is elsewhere talking to someone. Talking about Dobsonian, I must still finish this off and also add it to my site, but I since took the off-cuts (eg, the cut-outs from the split-ring, etc) and made a Dobsonian rocker box and base out of it, so I now have the option to go for the split-ring or just the Dob base. The split-ring is slightly more work to put up but is useful when I have a lot of people since it tracks automatically. The Dob base is nice and quick when its just me or a few others wanting to have quick look. The nice thing about re-using the off-cutts were that they needed minimal cutting since they were basically the correct size already - basically just needed squaring off. Please keep in touch with you progress and send some pictures of the final product. Happy ATM'ing! Willie