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Equipment Discussions >> Mounts

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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: what's the PE on the old AP 600E and 800 mounts? new [Re: orlyandico]
      #5546387 - 11/29/12 10:39 PM

Thanks Orlando. The NJP has conical bearings which probably work better than the ones in the 600.
Have you tried replacing the bearings? I know that with Tak mounts the bearings are easy to replace and they are inexpensive.


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: what's the PE on the old AP 600E and 800 mounts? new [Re: andysea]
      #5546419 - 11/29/12 11:04 PM

I would if I could.. but the 600 doesn't use bearings (it uses brass bushings)... that said the tolerances on those bushings is very high - like I mentioned in the other thread I tried to wrap 0.025mm (1 mil) PTFE film around the declination axis, and it would bind. So the tolerance is < 0.001"

I suspect this is the same design as the 900QMD - which is why AP actually has a "900QMD declination upgrade" program which gives the 900QMD the declination axis of the 900GTO.


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andysea
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Reged: 09/03/10

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Re: what's the PE on the old AP 600E and 800 mounts? new [Re: orlyandico]
      #5546434 - 11/29/12 11:17 PM

duh that completely went over my head. I understand now.
That's not a very good design is it? I don't see how having two meal parts against each other would provide smooth motion.
I suppose the bushing is the softer metal while the shaft is the hard metal. Given the extremely tight fitting of those parts, as soon as the lubricant wears out, the soft metal probably wears out too and My guess is that your stiction problem is caused by the parts having a minuscule amount of play. Once the load is off to the side that will cause the shaft to bind. Correct? Are the bushings proprietary design? not replaceable?


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orlyandico
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Re: what's the PE on the old AP 600E and 800 mounts? new [Re: andysea]
      #5546441 - 11/29/12 11:22 PM

I took apart a Vixen GP and it also had bushings.

I would not consider this to be "bad design" - Ed Thomas can probably weigh in here but well-made bushings would probably outperform poorly-made bearings (like those in the China mounts).

This is also why you've got a lot of folks replacing the bearings in their China mounts with Timken or SKF bearings.

I had thought about replacing the main declination bushing with a large bearing - but it would require massive machining and destroy the value of the AP600 as an antique / collectible.

There used to be a long waiting list on AP600's - I can imagine Wally toiling at the mill / lathe making each of these by hand without benefit of CNC


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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: what's the PE on the old AP 600E and 800 mounts? new [Re: orlyandico]
      #5546498 - 11/30/12 12:15 AM

True. I would not venture into a re-machining project. Yes Ed would probably have a better insight into the design. Could the bushing have worn out unevenly? Maybe the mount was used at the very limit of it's payload for a long time. Every time you have the scope pointing up, that would have put an uneven load onto the bearing surface of the bushing. I assume that the bushing, once in place does not rotate which means that the same portion of the bearing surface is always subject to the same load each time the mount is in a certain position.
Was the mount in a permanent setup? Ram mentioned to me an old thread where the owner of an NJP had the mount in a permanent setup for the longest time. That caused the gears to wear unevenly which eventually started to show up in their imaging sessions. DIfferent issue but somewhat possibly related.


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orlyandico
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Reged: 08/10/09

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Re: what's the PE on the old AP 600E and 800 mounts? new [Re: andysea]
      #5546518 - 11/30/12 12:35 AM

I'm fairly sure the mount wasn't used in a permanent setup, as the previous owner also had a 1200DA...

Well I'll buff the bushings as Ed says, use the anti stiction grease, and see...


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zerro1
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Reged: 08/02/09

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Re: what's the PE on the old AP 600E and 800 mounts? new [Re: orlyandico]
      #5546873 - 11/30/12 09:44 AM

Hello

The actual ingredient of the "limited slip" additive is jojoba oil.


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EFT
Vendor - Deep Space Products
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Reged: 05/07/07

Loc: Phoenix, AZ
Re: what's the PE on the old AP 600E and 800 mounts? new [Re: orlyandico]
      #5546938 - 11/30/12 10:30 AM

Quote:

I took apart a Vixen GP and it also had bushings.

I would not consider this to be "bad design" - Ed Thomas can probably weigh in here but well-made bushings would probably outperform poorly-made bearings (like those in the China mounts).

This is also why you've got a lot of folks replacing the bearings in their China mounts with Timken or SKF bearings.

I had thought about replacing the main declination bushing with a large bearing - but it would require massive machining and destroy the value of the AP600 as an antique / collectible.

There used to be a long waiting list on AP600's - I can imagine Wally toiling at the mill / lathe making each of these by hand without benefit of CNC




There is certainly nothing wrong with a well designed and implemented bushing system. The precision needs to be high though and wear could certainly be an issue faster than a bearing system. It might be possible for a good machinist to make a new set of bushings to replace the old ones. But I would want him/her to be a very good machinist to do it right.


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andysea
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Loc: Seattle, WA
Re: what's the PE on the old AP 600E and 800 mounts? [Re: EFT]
      #5547476 - 11/30/12 04:26 PM

So Ed,
Do you think that a bushing design would put the same amount of strain on the same portion of the bushing and overtime result in uneven wear? This should be inherent to the design, correct? Unless the mount is always perfectly lubricated.

Andy


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ohioalfa64
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Reged: 08/16/12

Loc: Ohio (NW)
Re: what's the PE on the old AP 600E and 800 mounts? new [Re: andysea]
      #5739164 - 03/17/13 05:19 PM

Alternatively, you can machine small Dimples in the bronze bushing and apply graphite impregnated grease. Canadian bridge design code uses this bearing design for minimizing friction (limited rotation) bearings. It is argued back and forth in the industry whether this really has a benefit or whether the graphite grease just mucks things up. The surface RMS of the shaft and bushing are both sufficiently polished?

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orlyandico
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Re: what's the PE on the old AP 600E and 800 mounts? new [Re: ohioalfa64]
      #5739864 - 03/17/13 11:51 PM

well... I managed to pull a 600-second unguided sub out of the AP600 last night.

The raw PE is about 8" and it gets down to 2" with a good PEM training (which took me a long time, because the 9000 controller is "dumb" and a really good polar alignment is required to avoid RA drift).

In summary... with a very good polar align, declination guiding is minimized and the DEC stiction issue can be side stepped.


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