CG-5 mount still seized.

[SteveBz]

Hi Guys,

After a few nice nights it's raining outside, so I'm sitting inside with my cg5 in parts. I've got to the bit where you loosen the grubs on the collar screw, here:

I need to turn the collar a few degrees so I can reach the grub screw.  But everything is frozen and nothing rotates.  I feel I have two options,

1) Drill a small access hole to reach the grub.  It probably won't do any long term damage, but it's a bit needlessly destructive.

2) Apply some heat somewhere to allow the dec to unfreeze and rotate to the right position.  I'm boiling the kettle as we speak.

Any ideas please,

Steve.

 

 

[Tiny Small]

Looks like the grub is fully screwed in? You could try heating the silver and cooling the black, but it probably won't work as it's unlikely to have created micro-welds on the surface. It's more likely that it has turned under force and the grub  has gouged into something. Take the easy option and drill it.

 

[SteveBz]

Hi Tiny,

Well I've had some success. I held the whole thing with a tea towel while my wife poored hot water on the outer sleeve, here:

The inner sleeve turned to the right position and I could unscrew the grubs.  same procedure with the second bolt.

Then all 3 sleeves returned to being frozen. Same solution for each sleeve.

So here's the main problem. This wormgear collar is just too small:

You can see some wear grooves and pockmarks. Really it probably needs to be ground out half a millimetre or less with a lathe.

Failing that some carborundum paper.

What do you think?

I bought it off eBay and I think it can never have worked.

Regards

Steve.

[SteveBz]

Actually, I'm not sure about the wormgear collar any more. It may be an innocent bystander here. I think what has happened is that a previous owner has pieced two cg5 mounts together. All three friction surfaces of the inner d3c mechanism are two big. Here:

And here:

I guess outer surfaces will be easier to shave down.

I'll wait till the next astronomy club meeting and see if anyone has a lathe.

In the meantime, ideas welcome.

Regards

Steve.

[Tiny Small]

If they were all from the same model of mount, they will have been machined to the same tolerances and the fact that they fit together suggests that those wear marks are likely a case of thermal expansion with insufficient or inadequate lubrication. Might be worth polishing with some rubbing compound from an auto shop then applying molybdenum grease. It's long lasting and handles changes in temperature really well. It comes in different thicknesses and can be diluted with engine oil. Bearing grease is also good but is likely too thick for this application. Molybdenum can be applied very thinly.

[Tiny Small]

Did you clean these or did they come apart like that? the worm gear should have a thick coating of bearing grease on it. In fact, any mating surfaces that move relative to each other need to be well lubricated.

[SteveBz]

Hi Tiny,

Well they don't fit. Only with a hammer.  so I 5hink they are possibly from different models. The dec worm collar slides beautifully and looks much older than the innermost dec shaft, which I think is newer and doesn't really fit.

I have some corundum powder, which is probably similar to rubbing powder.  I'll try it later today.

Tx

Steve.

[Tiny Small]

Any moving surfaces should be a close fit; tight but with enough leeway for a thin coating of lubricant and any surfaces that are static in relation to each another should be a very tight fit. As an example, head stock bearings in motorcycles are machined to such a tight tolerance that you normally have to freeze the bearing and then use either a press or hammer and drift to get it into the headstock as the outside diameter needs to be static relative to the headstock but the race needs to be free to move. It's hard to tell from the photos what goes where and how they move in relation to each other so useful advice may be difficult to give. I have an old cg5 at home so if you are still having trouble next week when I get home, I'll strip it down and see what I can find out that might help.

[barrie greenwood]

I would try to polish it rather than turn it down on a lathe or if you do have access to a lathe polish it on the lathe the higher the polish the smoother the results when it's back together

Regards Baz

[SteveBz]

1 hour ago, Tiny Small said:

Did you clean these or did they come apart like that? the worm gear should have a thick coating of bearing grease on it. In fact, any mating surfaces that move relative to each other need to be well lubricated.

No I cleaned them and relubricated them with Silicone lube. But they remained seized.

[barrie greenwood]

Yeah its to tight a tolerance a good polish should free it up and make it smooth it's only aluminum so it should polish up pretty easy but a high speed lathe polishing would work well

Regards Baz

[spaceboy]

I have continued in this thread here:

In spite of my skepticism the kettle trick worked like a dream. It looks like two eq5s from different scopes stuck together. The dec shaft seems to be the foreign one.

I worry that wet and dry will create unevenness. Should I try, or try to get someone with a lathe?

What are the pros and cons?

Steve.

 

 

Hi Steve

When recommending giving it a once over with the wet and dry this is to smooth out any high spots in the mass produced castings to in effect "hone / tune" the mount components not to directly alter the dimensions of them.

I will be honest with you in saying I'd cut my losses and try and acquire another mount or at least put a wanted advert up for a donor mount / parts. You could well run up costs having the part you have turned down to fit but if it is a part from another EQ5 clone then there is still no saying it would work as it should. The last EQ5 I purchased I spent almost an hour fiddling around with it before handing over the cash to make sure it was in full working order. The trouble being is the EQ5 is affordable where the larger HEQ5 & 6 are a significant investment. For this reason you get a lot of beginners use them and often do not balance scopes correctly or overload the mount causing all sorts of problems inside the mount that are not always apparent from first glance. With the lack of spare parts for astronomy gear people often pic up what they can when they can but as you have found out this doesn't always work.

With out being able to see the mount and parts in person it is hard to say whether it is just a case of a tight fit and all that is needed is a bit of feathering. It has been a while since I have stripped an EQ5 but if my memory serves I do remember the tolerances being tight and if you weren't completely square on when putting stuff together you could be forgiven for thinking they were the wrong parts.

The best person to ask about this stuff is astrobaby and she actually offers (or did) strip, tune, re-grease service for an affordable price and I believe is based around the London'ish area. But again you could find yourself picking up a head only EQ5 / CG5 for £30-£60 depending on condition and weights etc so it depends on what you already have invested in the mount. I hope you left the seller bad feedback what ever the case!!!

[Tiny Small]

28 minutes ago, spaceboy said:

Hi Steve

When recommending giving it a once over with the wet and dry this is to smooth out any high spots in the mass produced castings to in effect "hone / tune" the mount components not to directly alter the dimensions of them.

 

Exactly this. Polishing with a rubbing compound will take off a few microns at best, which may be enough, but sanding is an entirely different matter. I would stay away from sanding unless it's a very fine sand with >2500 grit wet (used to take microns of lacquer prior to polishing). 

[triton1]

As above I mated a eq5 Dec with my cg5 and with a honing stone works perfect thx to astro baby works great no problems 

[SteveBz]

19 minutes ago, triton1 said:

As above I mated a eq5 Dec with my cg5 and with a honing stone works perfect thx to astro baby works great no problems 

Hmmm. A honing stone, you mean like a stone to sharpen chisels? I have one on the garage.

[glowjet]

Steve, Just a suggestion, if your are going to have a go at trying to mate the parts together, there is a possibility that it is not binding all round, but may have high spots. Treat yourself to a little tube or tin of Stuarts Engineering Blue, quite inexpensive and available off the Bay. This way you will be able to see where to take off metal and not from areas that don`t need it  

[triton1]

Yes exactly that just remove any high spots regrease and you should be good to go.

[SteveBz]

Hi Guys,

After 2 hours with wet and dry the worm gear fit perfectly and performed beautifully, great stuff.

 

Now the RA. Hmmm... It's really stuck. The instructions for the polar mount are wrong.  You can follow them, but actually the whole part unscrews in one piece and you don't need to dismantle it.  Then instead of all the promised plastic washers I have real bearings, like off a bicycle.  The top one comes off. Then you need a rubber mallet to dislodge the bearings from the housing. A kettle of hot water is needed to get the worm gear over the inner cylinder and bearings.

I've now been sanding with 1200 wetndry for two evenings for an hour or more each time and maybe I can get it 3 mm further on. There's 20 or 30 mm to go. It seems unending and then there's the danger that I'll sand unevenly. I've bought some of that Engineers Blue so maybe that will help.  It arrives next week.

Will I get this mount sorted this year even?

Regards

Steve.

[SteveBz]

On 10/09/2016 at 17:46, SteveBz said:

I've now been sanding with 1200 wetndry for two evenings for an hour or more each time and maybe I can get it 3 mm further on. There's 20 or 30 mm to go. It seems unending and then there's the danger that I'll sand unevenly. I've bought some of that Engineers Blue so maybe that will help.  It arrives next week.

Will I get this mount sorted this year even?

 

Ok, great news.  The mount is sorted.  Everything is sanded down and running nicely.  The whole rig is set up and looking smooooth!

Now I just need a drive, but all things in good time.

Thanks for your help people,

Regards

Steve.