EQ mount maintenance

[morls]

Hi,

I'm really enjoying my first EQ mount, a Vixen Super Polaris purchased through the classifieds here (thanks Phil!). It tracks really well for visual observation, and is coping remarkably well with the 10kg or so I'm asking it to carry.

I was wondering about maintenance practices with these mounts. There is no way I want to pull it apart myself unless absolutely necessary, and it's working so well that I'm not even considering that. There is, however, a bit of free play in both RA and DEC, and I wonder if there's a way to address this without resorting to open surgery? It's certainly not a major issue, but I have very little experience with EQ mounts and so am curious as to how others have dealt with this type of issue?

Cheers

Stephen

[morls]

As an addendum to this post, I've found this guide:

http://web.archive.org/web/20050212130150/http://www.jbastro.com:80/SPb2.htm

Before I jump in, are there any potential pitfalls to be aware of?

[morls]

I've also found there's a screw missing, so first job is to get the specs and then pop down to the local bolt shop...

[morls]

The missing screw is an M5, and was easily found at bunnings. I'm impressed that a mount of this vintage is metric.

I've done some adjustments as per the guide linked to above, which very clearly explains, with photos, what to do. I think the finer tuning will be something I learn as I go, each mount having its own idiosyncrasies.

There's an issue accessing one of the RA worm adjustment screws - the mount for the motor is partially obscuring this, and is riveted in. If necessary I could drill out the rivets and replace with screws or bolts, but I'll see how it goes in the next while before going down that path. The play and backlash are already better on this axis after initial adjustments, so hopefully it'll be ok.

Cheers

Stephen

[bojan]

If it ain't broke, don't fix it....

[morls]

:thumbsup:

[morls]

The RA axis is smooth as silk now, but the DEC isn't. I've removed the worm gear, and am wondering what sort of grease is recommended for between the outer sleeve and gear grooves? The worm gear is nicely lubricated, but the actual mount is quite dry.

[morls]

I've decided I have to strip down the DEC axis and regrease it properly. I'm going to follow the step-by-step description of a GPDX re-grease on this site:
http://arnholm.org/astro/index.htm
I think the principles will apply for my mount. Take it slowly, be methodical and make sure of each step before going on.

The RA axis is smooth and I'm not touching that...

[Stonius]

What grease is a good question. Losmandy use Moly Paste, but it's stupidly expensive, at least for the ones with a proper high percentage of molbdenum content.

Other than that you want ones with a wide rating for temperatures.

Then there's viscosity that I don't know about. Maybe someone else wants to chip in here?

Markus

[morls]

what about something like this:

https://www.penriteoil.com.au/products/molygrease
https://www.supercheapauto.com.au/p/penrite-moly-grease-tub---500g/1935.html

[morls]

or this, supposed to be >40% Moly:

[Stonius]

Yeah, it's only 3%. The high moly pastes have a much higher concentration. That's what makes them so $$$

[Stonius]

That's probably better, but i can't find the post. I used to know the exact one that he uses.

But I'm no expert. And if it's not a Gemini mount, maybe they use other lubes. I'm no expert here.

[morls]

bought this, will give it a try and see how it goes.

70% MOLYBDENUM DISULFIDE GREASE - https://www.ebay.com.au/itm/70-MOLYBDENUM-DISULFIDE-GREASE-10g-2g-MOLY-LUBE-AIR-RIFLE-ATV-SPLINE-BMW-AR15/152289836930?var=&hash=item23752e7f82

[Stonius]

That seems pretty reasonable for that concentration. Let us know how you go! :-)

[morls]

Well, I've found something that might have been causing the issues with the DEC axis. There was a piece of paper at the bottom of the casing, and the grease here is very sticky, brown and quite hard. Photo 1 shows this.

There's quite a bit of clean grease everywhere else, and in the cavity at the top of the DEC shaft there's a lot, even though there are no moving parts here. Makes me think it's almost like a backup supply or something. Photo 2 shows this.

[morls]

I've cleaned up everything, and it's really good to work on something of this quality. It must be at least 30 years old, but it's in great condition.

However, there's an issue I need some advice on if there's anyone who could help please? There is some pitting in the aluminium casing which the brass gear sleeve sits on. When assembled there's a nylon washer between the brass and aluminium, but I don't know whether to try and fill these pits before reassembling, or trust that the moly paste and nylon washer will stop further damage. My concern is that if I leave it, the pitting might progress as there are now edges to catch and cause friction.

Can anyone offer advice on how to repair this, or whether I should just leave it? Everything else is in great condition, and I think there's still a lot of life in this mount. I've included pics of the beautiful brass gear too, very happy with how this has come up, and it's beautifully machined.

Cheers

Stephen

[bojan]

This pitting is normal for aluminium cast, just ignore it - it will not progress.
If you do not have nylon spacer, you can cut one from plastic foil used for printing transparences - they are very tough.

[morls]

Thank you Bojan.

I picked up some of the Suzuki moly paste today for $15, so I'll put things back together and see how it works.

[morls]

Well, the mount is back together and everything went smoothly (sorry). The mount and scope are reunited awaiting hopefully half-decent skies tonight :D

I've never used moly paste before but I have to say it looks the goods. The tube I got from Suzuki was 50g, cost $15.00, and I reckon I would have used about 10g, which included covering the gear sleeve completely.

It's made a significant difference to the amount of play, and the movement is silky smooth. I thought the RA axis was smooth, but now in comparison it isn't so I'll get to that next, maybe in a few weeks. I'm also going to try and track down a SCP insert for the polar scope, so will do both in an afternoon.

Thanks for the advice. :thumbsup:

[Stonius]

Good to hear! Nice work :-)

[Rkonrad]

Glad it works well well done

[morls]

wrapping up this post...

I've managed to attach the dovetail plate directly to the mount head. There was an issue in that one of the original connecting plates had come off, but a resourceful previous owner had drilled a hole in the head itself which allowed a bolt to connect a second plate, on top of which the dovetail plate was attached.

I've tapped a new hole in the dovetail plate, so this extra plate is not necessary. Saves almost 700g weight on this axis, so I'm very happy.

Cheers

Stephen

[morls]

A last note on the moly paste too...

The Suzuki paste is very good, and comes in a 50g tube. The paste from ebay is 10g, and probably isn't enough for both RA and DEC. Around the same price for each.

[The Mekon]

Great job Stephen. - but I have serious concerns with the second picture.

My advice is never to put an scope on the mount before first putting on the counterweights - you cannot trust those clutch locks which someone (even yourself) may inadvertently unlock.

[morls]

Thanks for the advice John. It's my first GEM so you've probably saved me from a disaster!