Which grease for EQ6?

[MarkS]

Which gease should I use inside the EQ6 - I'm going to do a stripdown, clean and regrease.

I'm sure white lithium used to be the recommendation but I've seen references on astro sites and bicycle repair sites that it stiffens in the cold (not a desirable property for winter imaging nor for winter cycling) and that a teflon based grease might be better.

[Rocket Pooch]

White lithium grease

[Mike]

You want the kind of white lithium that is mixed with Teflon or PTFE.

This stuff has Teflon in it: http://weldtite.co.uk/products/detail/lithium-grease-tube-40g (All of the Weldtite TF2 range has)

A lot of cyclists use it as it can cope with all weather extremes.

[MarkS]

This stuff has Teflon in it: http://weldtite.co.uk/products/detail/lithium-grease-tube-40g (All of the Weldtite TF2 range has)

Excellent - that's exactly what I already bought in the cycle shop at lunchtime!

[The Thing]

Exactly what I used as well.

[JohnP]

Well I used to have some white Lithium grease.. I remember lending it to Chris once when he was doing a rebuild.. Haven't seen it since.... ...

[JohnP]

Mark - will be interested to hear how you get on with strip down - I think I may tackle mine when I get back from France... John

[MarkS]

Mark - will be interested to hear how you get on with strip down - I think I may tackle mine when I get back from France... John

I have two to do!  I'll check the success of the first one before attempting the second one.

[JohnP]

Well Mark - I know you are the sort of person that'll do a full before & after analysis so I look forward to results/ numbers - I am also considering the belt mod... John

[MarkS]

So, here's how the strip down went.  I followed the procedure on http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20Strip%20Down%20Home.htm

The Philips screw holding the RA lock lever was very stiff.  I had the brilliant (NOT!!) idea of using my cordless impact screwdriver which chewed the head magnificently.  I then had to cut a slot in the screw head using a hacksaw so I could use a slotted screwdriver on it.

For removing the polar finder and the RA main bolt a boa constrictor tool worked really well.

Inside, everything was very clean, no swarf and none of the thick gloop that one always reads about.  The grease was clean and resembled vaseline.  In any case I cleaned it up and replaced it with Weldtite TF2 - a white lithium and teflon mix.

The bearings are all sealed and seemed to run freely so I didn't remove them except for the worm bearings which I did remove.  Again they ran freely but were sealed so I put them back.

It all went back together fine.  The main axes rotate more freely than before and there is no longer any free play.  This was the main benefit of the operation - I know know exactly what needs to be adjusted to cure various issues.

All in all it took 4.5 hours.  Do I think it'll reduce Periodic Error?  Probably not because I did nothing major to it.  The teeth on the gears had some sharp edges and maybe they could benefit from some attention.  I think that is the main thing that could possibly reduce PE.

So then I took a quick look at my recently acquired NEQ6.  I quickly identified the cause of the noisy gear "chatter" that these mounts have:  the 36 tooth transfer gear (attached to the motor assembly) actually rattles on its axis.  I also quickly found that the RA worm bearings were binding. So I aborted the job and I'll get some replacement worm bearings.

I don't think the build quality of the NEQ6 is as good as my EQ6.  It's certainly far noisier because of that gear chatter.

Reassembling the NEQ6 was a nightmare.  As I reinstalled the mount base onto the RA axis, the brass RA ring gear became jammed inside the mount housing because I introduced the RA axis into the mount base at a slightly squiffy angle and the tolerances between the brass gear and the internal walls of the housing are very small.  It took an hour of partial disassembly and judicious tapping to free it again and I then had to smooth off the ridges the jamming had caused in the aluminium housing and on the brass gear itself.  Just as an experiment I lowered the brass ring gear back into the housing to check all was OK and managed to jam it in again.  Nightmare!  I don't understand why there is so little room for it inside the housing.

On my third attempt I installed the taper bearing beforehand and as I introduced the RA shaft into the housing I ensured the shaft was absolutely central in the taper bearing.  The brass ring gear then didn't touch the internal wall of the housing.

To be honest, I don't really want to touch the NEQ6 again!

[MarkS]

Regarding the rattling transfer gear on the NEQ6,  here is a procedure for removing the play:
http://deepspaceplace.com/eq6.php

On the EQ6, although it didn't rattle, there was quite a lot of slop in the gear which the above procedure would also cure.

In addition, the teeth meshing on the NEQ6 transfer gear was not at all good - there was too much gap between the motor gear and the transfer gear leading to backlash and almost certainly increased PE.  Transfer gear can be moved closer to the motor gear by slackening the 3 hex bolts holding the plate, sliding the plate slightly and retightening.  Put 2 layers of foil between the meshing gears first, to get the meshing corect.  Astro-baby and others discuss it in this thread:
http://stargazerslounge.com/topic/64322-hypertuning-the-eq6

So, I need to remove the motors again!

[MarkS]

I adjusted the play in the transfer gear on Sunday and last night I got a chance to test out the EQ6  before the mist rolled in.

The verdict?

My weekend strip down, regrease and gear play adjustment has made no difference whatsoever.  The periodic error is still obstinately +/- 12 arcsecs and it is characterised by a sum of different period sinewaves so it is pretty non-repeatable, worm cycle to worm cycle.  Guiding showed no noticeable improvement.

I did manage to record a multi-worm-period PEC using PERecorder but didn't get a chance to test it before the mist descended.  PERecorder is very closely bound into ASCOM which means it is able to produce a chart of RA error against exact motor position where the motor position is measured in microsteps in the range 1-9024000 since 9024000 is the number of microsteps in a full 360 degree rotation of the RA ring gear.  Unfortunately PERecorder only works with a old fashioned webcam (not a QHY5 nor a Imaging Source DMK) - lucky I've still got one with a monochrome CCD lying around.

As an aside, if PHD is used instead of PERecorder, it is only able to record RA error against time.  So when PECPrep picks up a PHD file, it must convert time to microsteps.  It does this by multiplying seconds by 105, which is inexact (it ought to be 104.73).  This produces an accumulative timing error of more than 1 second every worm period, which to my mind is inexcusable.

[RobertM]

In a way I'm not so surprised though it's a pain it was you that had a tight bearing fit. I am however surprised it made no difference at all.  I wouldn't expect the PE to change much but the smoothness of the curve should be better which will help guiding.  That's what I found - if you're guiding then does PE matter that much.

Robert

[Rocket Pooch]

I'm still curious to see a graph of the PE....

And scared that the later mount seems to have a worse build quality than the EQ6...

[MarkS]

I'm still curious to see a graph of the PE....

And scared that the later mount seems to have a worse build quality than the EQ6...

The EQ6 PHD logs are here:
http://www.markshelley.co.uk/webdisk/PHD_log_09Sep13_unguided.txt
http://www.markshelley.co.uk/webdisk/PHD_log_09Sep13_guided.txt
The seeing was pretty bad when they were recorded.

I'll turn them into a graph at some point.

I think my EQ6 came from a good batch much later than your earlier bad batch example.  But on the NEQ6 they've made some changes - especially to the way the transfer gear is retained - this makes it rattle badly when starting and stopping slews.  All the NEQ6s I've come across are very noisy as a result.  It seems to guide with exactly the same RMS error as the EQ6 though (I've had them running side by side in the obsy).  I haven't yet done a PE chart for the NEQ6