628 Drive Problems
Posted 03 December 2012 - 01:26 PM
Posted 03 December 2012 - 03:39 PM
If it's turning, try torquing the three clutch pressure screws down a little tighter. Just be careful not to strip them.
Posted 04 December 2012 - 09:44 AM
Posted 04 December 2012 - 10:07 AM
Posted 04 December 2012 - 01:57 PM
Posted 04 December 2012 - 04:41 PM
Doesn't that put stress on the motor?
Not if the scope moves. And not if the clutch disengages when you move the scope manually. You can put a lot of torque into a pinion gear from a worm, but because of the mechanical advantage of the worm, not so much the other way around.
You should be able to find a happy medium with the screws. It might change with the temperature (mine does a bit).
Posted 04 December 2012 - 05:04 PM
Posted 06 December 2012 - 12:08 PM
Posted 06 December 2012 - 12:35 PM
Make sure your polar shaft moves freely with the 3 clutch screws loosened off, say a full turn or so.
Did you test the scope balance, with the polar shaft horizontal and dec shaft at 45 degrees.If it moves it's not balanced. You'll notice many Cave's and other scopes have a extra weight system on the tube to balance the tube radially to compensate for the weight of focusar eyepiece and finder.
Check to make sure the worm gear turns freely and leave a touch of backlash. Make sure the worm and worm wheel turn freely when the clutch is loosened.
Posted 06 December 2012 - 12:48 PM
Posted 06 December 2012 - 06:45 PM
Posted 07 December 2012 - 05:40 PM
It's up to you but I would replace the plastic split washers with metal ones and keep the old plastic one in storage to refer to when needed.
Posted 08 December 2012 - 11:11 AM
Posted 23 December 2012 - 12:48 PM
Posted 24 December 2012 - 12:38 AM
It sounds like something is contracting when it gets cold enough and is slipping loose then, just my W.A.G.
Posted 26 December 2012 - 09:54 AM
Posted 26 December 2012 - 10:43 AM
Pics would help a lot for seeing what you are referring to. There were steps we would take while assembling these to make sure everything was working before be buttoned them up and shipped them out. I might be able to remember the steps if I could see a pic, especially where you think the problem is.
Posted 26 December 2012 - 12:20 PM
Basically C and F are tightened with the 3 screws, with the worm wheel E: in the middle, and D: 2 thin teflon disks on each side. H is a teflon ring that goes into the wormwheel bore.
B and C are setscrewed to A the polar shaft.
Posted 26 December 2012 - 12:55 PM
Posted 26 December 2012 - 04:34 PM
Posted 27 December 2012 - 01:28 PM
When we put the mounts together, we tested them as we assembled them on a bench. First, we made sure the motor was turning by putting a tape "pointer" on the shaft and watching it turn. Then we put the motor on and marked a tooth of the ring gear to see if it moved while we did other things. At this point we might have left the clutch loose, I can't remember. But you could do that test with the whole scope assembled or without the ota or counterweight.
Remember, the worm wheel only turns on e in a day, so you need to wait a while to see the motion. Alternatively, you could set up on the sky and see if its tracking pretty quickly. There will likely be some backlash at first, but so long as the worm and worm wheel are making contact and the motor is running, you should see the scope start tracking your object in under 30 seconds or so (a lot of backlash!)
Posted 27 December 2012 - 02:21 PM
I'm a sad case for documenting my work, and getting it all posted here where it counts. I've completely done this drive and whole mount from inside out. The string is here:
There are pictures and process on the drive that I've never posted. Everything was redone and aligned with calipers and micrometers. This is a busy week and I have to jump on an Orion XT8i today. I'll get a few pictures now. I'll get you through this thing dot and tittle. Mine is complete, correct, in good shape, and works excellently. Originally this had an 8" on it. It now goes with a 10" that was offered on this mount from the factory. here's a picture of the basic clutch. The lock ring (far right) is first on the RA shaft and sets the end play in the mount housing.
The clutch starts with the large hub (center). This gets a teflon washer, ring gear, another teflon washer, and cover (upper left). All this is CLEAN, no lube, certainly no grease! I do use a special dry Teflon lube on some of these, but don't remember if I used it on this one. I could use some lube on my brain. Note that gear ring center!!! it has a small teflon strip around the inside. This goes between the gear fing and the hub. It makes the ring tight on the hub. The worm gear ring is thus isolated from everything with a washer top and bottom and a band around the center.
Posted 27 December 2012 - 02:29 PM
The worm had more endplay than it should. It should be right at zero without binding. I put a socket over the end and used my metal vice to squeeze the brass (porous bronze?) bushing in till the worm rotated freely with just a hint of resistance at the tightest. The loosest position was probably in the tenths for clearance (.0001" = a tenth).
Posted 27 December 2012 - 02:47 PM