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Zeiss Coudé telescope rebfurbish

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#226 Peter Ceravolo

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Posted 09 July 2019 - 01:36 PM

Pictured here is the worm housing assembly. The spur gear system on the left is for manual slow motion input while the clutched 40 tooth gear on the right is part of the RA drive train.

The assembly process is painless given the parts are pinned for alignment. The small set screws on either side of the assembly act as thrust bearings and align the 40 tooth gear on its worm. The alignment is a bit tricky having to snug and back off on the screws and lock nuts while rotating the small worn shaft in both directions trying to avoid any excessive friction or binding.

 

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The thrust bearing is actually a steel ball ground flat with the flat face in contact with the end of the large worm shaft. A bit of grease holds the half ball in place while threading the screw in place.

 

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IMG_0387.JPG


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#227 Steve Allison

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Posted 10 July 2019 - 01:38 PM

The Zeiss design details are fascinating. 



#228 photomagica

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Posted 15 July 2019 - 11:46 PM

I thoroughly support the idea of using modern servo electronics and relegating the East German control system to the "museum." East Zeiss control electronics or electro-mechanics was surprisingly good for its day but required careful on-going maintenance of switches, relay contacts, motor armatures etc. East Zeiss was trying to accomplish something that was right at the limit of the technology of the day. Now servo technology makes something that was just adequate into something really slick.

Cheers,

Bill


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#229 Senex Bibax

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Posted 16 July 2019 - 07:14 AM

I thoroughly support the idea of using modern servo electronics and relegating the East German control system to the "museum." East Zeiss control electronics or electro-mechanics was surprisingly good for its day but required careful on-going maintenance of switches, relay contacts, motor armatures etc. East Zeiss was trying to accomplish something that was right at the limit of the technology of the day. Now servo technology makes something that was just adequate into something really slick.

Cheers,

Bill

Reminds me of my father's workplace, where they acquired a massive faceplate lathe (3 metres across) from East Germany in the late 1970s. Mechanically it was fine, but the control panel had to be completely rewired before the lathe was usable.


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#230 Peter Ceravolo

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Posted 16 July 2019 - 06:05 PM

There is another plus to replacing the old electronics: The last owner complained that the Zeiss coude did not have a Dec axis clamp, so if it wasn't balanced well you'd loose the field. The manual Dec drive is all spur gears, I figure an engaged geared head servo motor should easily hold the Dec axis in position.


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#231 photomagica

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Posted 16 July 2019 - 10:45 PM

Yes - a modern servo package will really be great. The periodic error can be squeezed down, backlash compensation enabled and high resolution tracking on the sun (or any object) will be really, really nice. Also it will be way easier to implement the modern servos versus servicing and trouble shooting the old electronics. And the 8" objective is a really good size for solar physics.

Cheers,

Bill



#232 Peter Ceravolo

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Posted 21 July 2019 - 07:54 PM

With the help of a few friends the massive RA shaft housing was placed over the massive RA shaft.

 

IMG_0425.JPG

 

Some time was spent cleaning the machined recesses for the motor and manual drive inputs. Industrial single sided razor blades, lots of them, are very handy for this.

 

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Then the drive components were tried on for fit. I have to say the locating pins make this very easy.

 

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But then there was this surprise, the motor drive component machined recess was much larger than the actual part and was off center, some bare metal was showing.

 

IMG_0429.JPG

 

This was strange as we took care to mask off the obvious mounting locations to ensure a good fit.

 

So I raced off to the computer to check the disassembly pictures to see how the area looked originally.

 

IMG_2420.JPG

 

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So there was no mistake on our part, the drive component fit as it should but it's clear that the recess machined into the massive RA housing was way over sized and off center. We're going to have to do what the Zeiss folks did originally - paint over what I assume is a machining mistake!


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#233 Peter Ceravolo

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Posted 31 July 2019 - 02:02 PM

Starting to see the light at the end of the tunnel with the Zeiss Coudé project, just finished reassembling the massive RA shaft.

 

You'll recall the RA shaft bearings sport wire races. Here is a layout drawing of the south polar bearing, note that it's not an accurate engineering drawing, it simply illustrates what's inside:

 

Wire bearing 2.PNG

 

With the help of a few friends we lowered the RA housing over the shaft. The housing seated nicely on the North bearing and rotated freely. Then came time to reassembly the south bearing, sliding the cage into position and inserting the new 10mm dia ball bearings:

 

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The cage had to stand a bit higher on the shaft than intended so I could position the balls. With all the balls in place I pushed down on the cage to lower it and the balls into position.

 

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Next I positioned the outer race and the ground spacers, but the outer race would not slide into place:

 

IMG_0443.JPG

 

I determined that the paint was too thick for the narrow gap between the RA shaft and the outer race. I had to scrape away the paint with a razor blade. I used a piece of cardboard to prevent paint chips getting in between the balls.

 

IMG_0447.JPG

 

That did the trick! The outer race slid into place nicely and housing rotate freely after the retaining bolts were tightened.

 

IMG_0452.JPG


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#234 Kokatha man

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Posted 31 July 2019 - 07:52 PM

Nice! waytogo.gif  Not on such large, precision machinery but I can relate to these fiddly little "on the spot" requirements, such as needing to scrape the paint away to get everything to fit together Peter...masking prior to the re-paint might seem more sensible in hindsight but on anything that is so complex/involved there's always going to be a need to think on your feet! :)



#235 Peter Ceravolo

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Posted 31 July 2019 - 08:42 PM

Well, that area was in fact painted originally. But the new coat was thicker than the old layer of paint, and the gap in the parts is tight so the new paint layer had to go! Details... details...



#236 R Botero

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Posted 01 August 2019 - 02:42 AM

Properly machined parts are made with minimum “a thou” precision; wouldn’t expect any less from the Germans. The layer of paint you applied was just a thou thicker. All is well now :cool:

Edited by R Botero, 01 August 2019 - 02:42 AM.


#237 Peter Ceravolo

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Posted 10 August 2019 - 08:45 PM

For the first time in a year the polar axis is now horizontal... A big deal really as I don't do any lifting or handling of these big parts without at least one extra set of hands.

 

For the first time I was able to try rotating the polar axis on the bearings with a radial load, all smooth!

 

IMG_0472.JPG

 

In this view one can see that there is a component with perpendicular alignment dovetail type slots circled in red.

 

IMG_0475.JPG

 

I'm only guessing, but I suspect it's to center the RA gear on the axis of rotation. But the adjustment screws are not obvious, probably buried within that part of the axis and I don't think I want to dig in that deep.

 

Here are close ups of the two slots.

 

IMG_0477.JPG

 

IMG_0478.JPG


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#238 Peter Ceravolo

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Posted 10 August 2019 - 09:05 PM

The big area gear is mounted on a slip clutch so the observer can manually swing the telescope around the RA axis. In the photo below the actual RA shaft is the blackish tube section extending to the left. I can grab and hold the RA gear stationary and still rotate the black portion of the massive hollow shaft.

 

IMG_0475-a.JPG

 

I have never actually used the telescope, I purchased it sight unseen. So as I'm reassembling the scope I'm learning how it works... :-)

 

I didn't know the function of this assembly of parts inside the axis until I started fiddling with it.

 

IMG_0473.JPG

 

It turns out to be the RA axis clutch clamp and it is actuated by a connecting rod extending down to the south side of the RA housing. In this view I'm holding what is (now) obviously the assembly that actuates the rod (not in place yet) that operated the RA clutch clamp.

 

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Here are some views of the clutch clamp knob with the internal gearing required for operation:

 

IMG_0483.JPG

 

IMG_0479.JPG


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#239 Peter Ceravolo

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Posted 12 August 2019 - 11:28 PM

Seeing that the large drive gear can be actively centered on the large RA axis, it occurred to me that what can be adjusted can also go out of adjustment. The RA shaft assembly was moved around a bit so I thought it would be worthwhile to check the main gears run out.

 

This is actually easy to do with a run out gauge on a magnetic stand. Happily I could see only about 0.001" or so of run out when the probe is placed on the big gear's chamfered edge. Of course I'm counting on the edge to be in line with the teeth, but I suspect it's a safe bet.

 

I also tugged on the shaft to see if there was any play in the bearings - zero.

 

IMG_0486.JPG


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#240 Peter Ceravolo

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Posted 15 August 2019 - 04:24 PM

I was just contacted by a fellow Zeiss Coudé telescope owner who informed me that the slots in the RA gear assembly are not for adjustment but in fact allow the gear to "float" on the shaft.

 

"I have just had a look at your cloudy nights thread and the new pictures

 

The dovetails you have circled in red are actually not for alignment but the opposite.
It is a very large shaft coupling that allows the gear to float on the polar axis, you should be able to slide the gear slightly about the polar axis.

 

This seems to me to be a clever solution to solve the problem in gear cutting that is the gear is never truly central so causes backlash at one side and binding at the other, very noticeable in most RA drives. One way around this is to spring load the worm but this has two major problems one being excessive wear to the gear and worm the second is wobble or jitter especially noticeable in windy conditions.

 

What Zeiss seem to have done is cut the gear and then remount the gear in the lathe by the outer of the teeth and recut the centre hole to match the gear.

 

The gear is then placed over the polar axis with play in it, the polar axis is machined truly central and the distance from the gear teeth to the central hole is now the same all around the gear. when you adjust the worm against the gear it slides the gear on the shaft coupling against the polar axis, the gap between the worm and the polar axis is now constant as the gear just moves to one side on the polar axis so the gear fills this gap.

 

What you end up with is no backlash and very little friction, so no wear and the motor can keep a more constant speed.

At first it seems complicated but is actually a very simple solution on a large scale.

If you cannot move your gear slightly I would say the grease has dried out and it would be worth striping, cleaning and regreasing at this stage, it is quite easy to do and also interesting."

 

IMG_0475.JPG

 

IMG_0477.JPG

 

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#241 Peter Ceravolo

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Posted 15 August 2019 - 04:28 PM

I could not, in fact, move the gear laterally at all, clearly the grease had turned to glue. So with the other owner's encouragement I disassembled the gear assembly. Not that scary after all!

 

IMG_0496.JPG


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#242 Kokatha man

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Posted 15 August 2019 - 08:33 PM

That's excellent Peter - even my aged & weary brain this early in the day for me could follow your correspondent's explanation of the mechanism - clever! waytogo.gif



#243 Peter Ceravolo

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Posted 16 August 2019 - 05:24 PM

There are a number of components whose bearings were caked with the old grease that, while they still moved freely, it would be ideal to clean and regrease.

 

IMG_0493.JPG

 

I didn't feel the need to disassemble everything, I simply soaked the component in varsol for a few days to dissolve the old grease. Spinning the shafts and brushing the bearings periodically did a good job of cleaning off the old grease.

 

But there were some components internal to the RA shaft that I could not get at, the screw heads were buried in the RA gear assembly.

 

IMG_0473.JPG

 

But the dissasembly of the RA gear hardware made it possible to detach the components and given them a thorough cleaning.

 

IMG_0494.JPG

 

Here is the Declination slow motion gear component:

 

IMG_0498.JPG

 

And the RA clutch/clamp:

 

IMG_0499.JPG


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#244 Peter Ceravolo

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Posted 18 August 2019 - 08:43 PM

It was fortuitous that the other Zeiss Coudé owner (who clearly prefers to be anonymous) encouraged me to take apart the RA drive gear assembly, it really needed a cleaning. Doing so also explained the function of a lubrication port that puzzled me.

 

It's circled in yellow in this view of the RA gear assembly prior to disassembly and cleaning:

 

IMG_0475-b.JPG

 

The lubrication port is circled in this pre disassembly image:

 

IMG_2332.JPG

 

At the edge of the monster, hollow, RA shaft there is a set screw that lined up with the center of the mystery component. I removed the set screw and stuck a wooden skewer stick in the hole and out came some grease from a number of holes along the length of the shaft:

 

IMG_0508.JPG

 

The two farthest holes along the shaft lubricate the RA worm gear. The first hole, closes to the port, lubricates the last "floating" ring. That ring also engages the RA clutch/clamp pad and is also lubricated by the hole.

 

In this image I'm using a household scrub pad to clean off the dried up grease on the worm wheel. The worm wheel's recessed inside diameter is painted but the two outer extremes of the ID ride on the polar shaft and are lubricated by the injection holes. The gear ID also has groves along the length to distribute the grease.

 

IMG_0514.JPG

 

I stuck a steel rod in the hole to force out as much grease as possible, then I installed the lubrication port and flushed out the rest of the old grease with fresh stuff.

 

IMG_0512.JPG

 

If you think that I'm actually enjoying all this.... well... you'd be right! smile.gif


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#245 R Botero

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Posted 19 August 2019 - 12:40 AM

Great progress Peter! We are enjoying your posts as much!
:waytogo:

Roberto


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