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Re: Stability Of E/Mount

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Posted by Doug Hudgins/">Doug Hudgins on September 9, 1998 04:46:11 UTC

: Are there any ATM's out there that can help me with a : small problem I have been having with my 12.5" Newt. on : a equatorial mount. I built the mounting years ago when : I was in the process of building a 8" Newtonian. A terrible : tragedy occured when the table I was using was knocked : over by our hound and cracked the unfinished 8" mirror. : After that episode I rebuilt a massive grinding table and : then proceeded with a 12.5" blank I had, building the : scope and other mechanics around the mounting. : My first problem is, the shafts and head are built to : support a 10-15lb tube assembly. The 12.5" scope is : considerably heavier, around 30lb. or so. My counterweight : total about 37lb. You can see I've got about 65lb sitting : on my fabricated aluminum tripod. A lot of weight. : The guts of the mount include 1" diameter shafts on the : R.A. and Dec. axis. It is built from machined steel pipe : and plate. The bearings are sealed roller bearings. : The scope tends to resonate when it's balanced, vibrating : with any movement east, or west. : Around the Dec. axis the vibration is not noticable. : The second problem is, with all this weight I am getting : quite a bit of backlash in my fabricated R.A. Drive motor : and gearbox. I have tried to compensate for the backlash : by un-balancing the scope, but to no avail. The gearing : is made of all spurs, no worms in this set. : I know there are ways to solve the backlash problem, but : what about the annoying resonances in the tripod and : equatorial mount. Has anyone else had a similar problem, : or offer any suggestions. : Thanks : Anthony

I can't really help, but I can comiserate. I have been struggling for years to use my 10" f15 classical cassegrain on an old sand-cast Astrola mount with 1 1/2" shafts and sealed roller bearings. My difficulties are much the same as you describe - primarily the annoying and amazingly persistant oscillation (resonance?) that accompanies any movement in RA. I have torn this mount apart, and rebuilt it from the ground up more times than I can count. I have rebuilt the complete drive/clutch/gear assembly at least twice. In the end, I just can't avoid the fact that the tube assembly is just too much for the mount.

What am I going to do? Surrender! I just got a line on a used Opticraft mount w/ 2 1/2 shafts - I'm going to give up the fight. Good Luck - maybe someone with more mechanical savvy will kick in a few useful suggestions.

Doug Hudgins San Jose, CA

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