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Equipment Discussions >> Classic Telescopes

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Geo.
Carpal Tunnel
*****

Reged: 10/01/08

Loc: Upstate NY
Re: 628 Drive Problems new [Re: dgreyson]
      #5589958 - 12/26/12 04:34 PM

The problem I've seen is that the set screws (3 as I recall) that lock B onto A will slip out of the land cut in A and move up A binding against the axle housing. But I remember that clutch pressure was applied by a large handwheel at the end of A.

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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: 628 Drive Problems new [Re: Geo.]
      #5591206 - 12/27/12 01:28 PM

From ancient memory, I recall that the worm wheel is a ring that rides in a step in c and f. The two Teflon disks D are rings that also ride in the step as clutch surfaces between the hubs and the worm wheel. Adjustment should be VERY sensitive, such that minor fractions of a turn of the clutch screws can make a big difference in the amount of friction applied. The lock washers were used to prevent the screws from loose ing on their own. They don't act as springs

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!)

Tim


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apfever
Carpal Tunnel
*****

Reged: 05/13/08

Loc: Colorado
Re: 628 Drive Problems new [Re: tim53]
      #5591271 - 12/27/12 02:21 PM Attachment (16 downloads)

Atl,

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:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4966686/page...

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.


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apfever
Carpal Tunnel
*****

Reged: 05/13/08

Loc: Colorado
Re: 628 Drive Problems new [Re: apfever]
      #5591275 - 12/27/12 02:29 PM Attachment (14 downloads)

Random picture:

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).


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apfever
Carpal Tunnel
*****

Reged: 05/13/08

Loc: Colorado
Re: 628 Drive Problems new [Re: apfever]
      #5591291 - 12/27/12 02:47 PM Attachment (14 downloads)

After positioning the bushing for end play, I installed the retaining bolt with just a touch of Red Locktite on the threads, and a micro hair amount at the contact point between the bolt head and bushing.

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apfever
Carpal Tunnel
*****

Reged: 05/13/08

Loc: Colorado
Re: 628 Drive Problems new [Re: apfever]
      #5591362 - 12/27/12 03:27 PM Attachment (16 downloads)

This is a back tracking. One thing you need to be sure of is that the RA shaft is rotating in the mount housing smoothly, freely, 360 degrees, no binding, no strain for the clutch/drive. If the shaft does not have propper rotation, don't expect the drive to run it correctly. I won't get into doing this here, but if it needs to be fixed then your into stuff like this:

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planet earth
Carpal Tunnel
****

Reged: 09/07/10

Loc: Ontario Canada
Re: 628 Drive Problems new [Re: apfever]
      #5592144 - 12/28/12 04:39 AM

Thanks for posting the pics and the link Neil.
Most helpful.
Sam


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Atl
professor emeritus
*****

Reged: 04/13/12

Re: 628 Drive Problems new [Re: planet earth]
      #5610866 - 01/07/13 08:31 PM

I found the issue and partly resolved the it. The drive motor is gunked up. I soaked it in wd40 while heating it with hand warmers then ran it for an hour with no issues. I am not sure this fix will hold up, but these motors were not made to open up. Any suggestions? However it is now running.

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dgreyson
scholastic sledgehammer
*****

Reged: 11/06/12

Loc: South Carolina
Re: 628 Drive Problems new [Re: Atl]
      #5611102 - 01/07/13 10:54 PM

WD 40 will evaporate and the dry film wont keep the old grease in suspension. Soak it in a good quality gun oil instead that wont dry out.

On stuck motors, as a last act of desperation on a sealed clock motor that wont turn I have a procedure I use to get them working again. synchronus motors use a thick grease on the gears and when its sitting for years not in use it eventually hardens into a solid concretion and the motor is stalled dead. To free a stuck sealed synchronus clock motor I take a decimal size drill bit, available at harbor freight, or any wire drill bit just so its very very small and drill a hole in the side or bottom near the edge away from the shaft. Too big a bit and you get metal chips in the works. Drill just enough to make an opening you can insert oil into, dont plunge the bit down thru the gears. next, use an Ink cartridge refill syringe, Insulin syringe or any other sorts of syringes that have a needle to fit in the hole you made. you can use even pen oilers that you could refill, those are readily available, and alternately squirt warm oil in and shake it around and then turn it hole down and squirt air in to blow out the dirty oil and any metal filings. if you use a small enough bit, the filings are small and insignifigant. repeat untill it comes clean. The old grease is like candle wax but it eventually will soften up. After it's clean put some oil back in again.

Plug it in and look at the window thats on most motors to see if the rotor is moving. If its still stopped, pry up the tabs on the plastic window and use a tooth pick or a needle to manually rotate the rotor without bending it. just push it to give it a start and eventually it will take off if the grease is soft enough or washed out. put the window back and bend the tabs to keep it and keep it running and watch it a few hours till you know its ok. Sometimes I have to work it with oil and pushing the rotor for awhile but eventually it will run. Last, clean off the hole and plug it with a smear of silicone.

Anyhow, thats what I do. put a piece of broomstraw on the gearshaft with a dab of wax and you should see it move eventually. If the rotor is moving but the shaft is stopped, you have a gear thats worn down, maybe stripped.
Better to replace it with a new motor.
It's possible to desolder the baseplate with a propane tourch and solder wick and xacto knives to prise it up but usually the motor is too worn out to do anything for it unless you can move a gear up a shaft to bear on an unworn part of the gear. Never had much luck doing that.


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Atl
professor emeritus
*****

Reged: 04/13/12

Re: 628 Drive Problems new [Re: dgreyson]
      #5611481 - 01/08/13 08:16 AM

Great ideas. The drive will turn it is just temperature sensitive. I bet soaking it in Breakfree would do it.

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rdandrea
Carpal Tunnel
*****

Reged: 06/13/10

Loc: Colorado, USA DM59ra
Re: 628 Drive Problems new [Re: apfever]
      #5612075 - 01/08/13 02:34 PM

Quote:

After positioning the bushing for end play, I installed the retaining bolt with just a touch of Red Locktite on the threads




That "retaining bolt" is actually how you adjust the end play. The oilite bushing ought to move relatively freely in the hole that's bored for it. It's the pressure of the "retaining bolt" that adjusts how tightly it presses on the worm. Red loctite might make future adjustments difficult.


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planet earth
Carpal Tunnel
****

Reged: 09/07/10

Loc: Ontario Canada
Re: 628 Drive Problems [Re: Atl]
      #5613126 - 01/09/13 04:04 AM

Quote:

Great ideas. The drive will turn it is just temperature sensitive. I bet soaking it in Breakfree would do it.



I hope it works out for you.
I was fortunate to find a new RA motor for $20.00 and about $20.00 shipping by posting a want ad on Canada Wide Astro.
Surplus shed use to have them and Bill Vorce (Telescope Warehouse), but I believe they are now both sold out. Worth checking out though in case they get any more.Posting want ads can really turn up some fairly rare ATM stuff.
Sam


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