NEQ6 belt mod completed

[JamesF]

Just before the bank holiday this arrived in the post courtesy of Auntie FLO:

Such was my enthusiasm for getting started that I'm not sure I have a photo of the contents, so until I find it (assuming it exists) I'll just have to say that in includes the separate kits for the RA and DEC axes (pulleys, belts, motor mounting plates and idler wheel plates), some allen keys, a pair of tweezers and six pages of detailed instructions.  Somewhat more daunting than the HEQ5 conversion I did very recently.  I'd watched a few videos of the NEQ6 belt conversion being done and it looked like a significantly bigger job.

On the positive side, the recommendation was again to leave the mount on the tripod (or pier in my case) whilst doing the work, which means I shouldn't need to redo the polar alignment afterwards.

James

[JamesF]

The first job was to remove the control panel by undoing the four outer screws (the inner ones hold the circuit board in place).  What's inside is actually pretty uncomplicated:

That actually looks less threatening than the inside of the EQ3-2/EQ5 after-market motor handset

The cables that have to be unplugged are all that the end near the top of the photo, neatly labelled, though actually all the plugs are different and keyed so it wouldn't be possible to put them back the wrong way.  The RA connection is a bit odd in that it runs down the inside of the mounting posts for the circuit board.

It was a bit fiddly to get back on at the end, but nothing major.

With the circuit board removed access to the motors is pretty straightforward:

The RA motor came out very easily by undoing the two large screws.

There was a small disaster when I tried to do the DEC motor though.

Fortunately I was able to fish all the broken bits of screwdriver tip out of the inside of the mount without them disappearing anywhere awkward.  And then I found a better quality screwdriver to complete the job

James

[JamesF]

Next the entire DEC axis has to be removed, starting by unscrewing the collar for the counterweight bar, which comes off very easily.

There's a tapered roller bearing at this end of the axis which could potentially fall out when this is removed, though mine didn't and I'd generally expect it to stay in place.  It is likely to fall out when the entire DEC end is now lifted out of the mount though, so you need to have one hand ready to catch the bearing whilst using the other two to lift the DEC axis out of the mount.  Some videos show the removal being quite awkward and I was prepared for a bit of a fight, but mine lifted out very easily and I fitted the bearing that I dropped caught back on the end of the axis for the time being.

The instructions suggest leaving this to come back to later, so that's what I did, though if you're just congenitally unable to follow instructions exactly there's no reason the rest of the conversion work couldn't be done on this axis now.

James

Edited May 9, 2020 by JamesF

[JamesF]

So, RA axis next, starting with the polar scope.  This just unscrews.  I was almost tempted not to put it back at the end.  Now I have an observatory I only used it for a rough polar alignment before doing the rest with Ekos.

After that the collar with the pointer for the polar scope scale has to come off.  Just three screws this time.

And then the retaining collar for the bottom end of the RA axis.  This was a bit more awkward.  I've seen people use oil filter removal tools for this, but I wrapped some thick card around the collar and used a large adjustable wrench.  It wasn't actually that hard to turn once I'd got a grip on it so I didn't have to get out the Stillsons, and in fact once loosened by quarter of a turn I could turn it off using my fingers.

The RA clutch mechanism needs to be released at this point so it's free to turn easily and then the lever can be removed by undoing the screw holding it on.

The clutch mechanism can then be unscrewed by hand.  I wound it out a fair way so there was no chance of it getting caught on anything as the RA axis was disassembled, but there's a small brass disc on the end that might drop somewhere awkward if it's undone all the way, so it's probably best left in place.

After that the entire RA axis lifts out and you'll once again need to use your third hand to catch the tapered roller bearing at the bottom end in case it falls out.

A quick peer down the end of the remainder of the mount shows grease in places I'm sure it wasn't meant to be and some fairly dodgy casting at the bottom end.

Removing these four retaining screws from the worm housing allows it to be removed just by lifting it off:

Above the remaining bearing on the RA shaft you can just see a white plastic shim which needs to stay there, but I'm not going to touch that.  When I lifted the top bearing off the worm housing I found a couple more.

So I made a note that they need to go back between the two.  There's also an awful lot of grease here that doesn't seem to be serving any purpose whatsoever.

After undoing the screws that hold the DEC collar with the hour markings on, the worm housing just lifts off and it's time to visit the workshop.

James

[JamesF]

With the worm housing in a vice (protected from damage by the vice) I used circlip pliers to remove the worm end caps.  I do actually have the additional tool from Rowan astronomy for doing this, but circlip pliers were easier.

Then the retaining grub screws for the gear driving the worm need to be released.  I've seen people fighting with these in videos, but in my case they came out without too much pain.  Certainly they were tight and my allen key did flex a little until they first released, but they really weren't that bad.

Then the retaining collar for the worm needs removing.  I did use the Rowan Astronomy tool for this.  It's just a lot easier in this case to have something that fits perfectly.

The tool itself is on the left here:

After that the worm dropped out (together with the bearing at that end) after the lightest possible tap with a drift.  Again you need one hand for the drift, one for the hammer and one to catch the worm so it doesn't drop on the floor.  If you have a fourth hand to catch the gear as well, even better.  Or try to do the entire removal process with the housing laid down (my workbench has a handy lip on one end, fortunately).

I then used a larger drift to remove the remaining worm bearing as I'd decided to replace the worm bearings at the same time as doing the belt mod.

The new bearing for the gear end went into place very easily and after that it really was just a simple case of following the instructions to reassemble everything.  When fitting the new belt pulley I very lightly tightened the grub screw that bears against the flat on the end of the worm, stopping as soon as I felt any resistance.  Then I wiggled the pulley about a bit to get it pretty much central on the flat, lightly tightened it again and repeated the process until it wouldn't wiggle any more, finally tightening both grub screws fully.

The second grub screw protrudes a fair way out of the pulley collar even when fully tight.  It only just clears the inside of the motor housing. I reckon there's no more than 0.5mm in it:

Then it's back down to the observatory to refit the worm housing.

In fact I decided this was more easily done by propping up the RA casting, dropping the RA gear into place and then feeding the worm housing over the top:

(I also cleaned off all of the unnecessary grease and re-greased the DEC gear ring.)

The little brass block in the above photo is actually part of the adjustment mechanism for the worm engagement.  The grub screw in the worm housing pushes against it.

With the worm housing back in place I put the four retaining screws back in, but only tightened them just enough to stop the housing being able to move.  They get fully tightened after the worm adjustment is done.

Here you can see the belt drive where it comes through into the main motor housing.

With that all done, the entire housing can be replaced on the mount.

James

[JamesF]

Now it's time to return to the DEC axis.  The process is pretty much the same as for the RA axis, starting with the removal of the clutch lever (having remembered to release the clutch first).

The worm housing should then just lift off (note the plastic shims here, too).

At this point, replacing the gear driving the worm is exactly the same as for the RA axis, so here we are again with that all done.

Reassembly is pretty much identical too, at which point the DEC axis can be put back on the mount.  This was a touch awkward.  I had to try three or four times before everything dropped into place correctly.  I think it must be very sensitive to alignment and once I got it right everything just dropped into place easily.

That's most of the hard disassembly/reassembly work done.  All that remains is to modify the motors and refit them.

James

[JamesF]

The first step with the motors is to remove the mounting plate and idler gear.

And then the gear comes off the end of the motor drive shaft.

The new pulleys go on, together with the mounting plates.  Orientation is apparently important here, especially for the RA motor as the cable probably won't reach any other way.  I actually labelled my motors when I removed them just to make sure I got the correct mounting plates etc. on the right motor (the plugs are different on the cabling, so if you get them the wrong way around they won't go back on the controller board properly).

The plates holding the idler wheels go into the motor housing.  This was perhaps the most awkward part of the entire job for me.  The idea is that the tweezers in the kit are used to pinch the sides of the belt together and then the idler wheel plate is threaded onto the end of the tweezers and slid down their length so the belt feeds between the wheels.  My hands are just not small enough to make this easy in such a small space.  I have seen it suggested that an elastic band is looped around the drive belt before the axes are reassembled and that is used to pull the belts into place.  It's entirely possible that makes it easier.  Anyhow, after "quite a few" attempts, I ended up with this:

The DEC belt was an equal measure of fun, but I got there in the end.

Into the finishing straight now...  Refitting the motors was pretty straightforward although you do need a very long allen key or something similar to be able to reach far enough inside to be able to tighten the screws.  It is also a bit strange because you can't actually see if the motor pulley has engaged with the belt at all.  I removed the worm end caps again (only those on the side showing here) and turned the end of the worm with a pair of pliers whilst watching the end of the motor drive shaft to see if it was also turning, whilst using a flat-bladed screwdriver to very gently adjust the tension on the belts by moving the mounting plates, but it's still hard to know if you have enough (or too much) tension.  In the end I decided I was happy enough.

My kit was also missing a flat washer and a spring washer for one screw for the idler mounts, so I took them off one of the old screws that were not being reused.

After that it was just a case of re-routing the RA motor leads, plugging everything back in and refitting the fascia.

And this is what's left over:

James

[JamesF]

Of course this isn't quite the end of the job.  There's still the worm adjustment to do.  I twiddled with the grub screws on each side of the worm housing (the one on the curved side moves the worm closer to the gear, the one on the flat side moves it away) until there was absolutely no play in the axis and then backed them off by about one turn, which gave a lot of backlash.  I could then spin each axis through 360 degrees and check it ran freely.  Each time it did I increased the gear engagement by at most an eighth of a turn and tried again.  If the motor stalled or jumped at 800x slew speed then I backed it off a fraction until it didn't.

What I've found is that the motor might jump at 800x, but at lower speeds it seems fine.  I don't feel that adjusting it for the slower speeds is sensible though.  I don't want high speed slews stalling or jumping.  Unfortunately because there are clearly three or four very small spots where the meshing of the gears is just a little tight, this has meant that there's still obvious backlash in the RA axis.  A very small amount, certainly, but enough to be obvious.  The DEC axis on the other hand is very good.  There is backlash, obviously, but it is absolutely minimal.  I think this may need more work.  I have, for instance, been wondering if I can move those tight spots to a position where they'd never be used as they're all in the same quadrant of the RA gear.  I'm not sure that's feasible, but I'm not sure it isn't, either

The other thing I must mention is how astonishingly quiet the mount now is.  Even kicking off an 800x slew there's just the quiet hum of the motors.  If I can I'll try to post "before" and "after" recordings, but that's for another day.

James

[Brent]

An interesting read following that, thanks.

Probably not something I will ever do myself but have bookmarked it with other guides just in case!

[JamesF]

Prompted by lukebl's success at improving his RA axis backlash, this evening I returned to mine and ended up disassembling the entire axis once again just to make sure I'd put everything back together as well as I could.

In the process I discovered that whilst the instructions suggest that the entire process can be done with the mount on the tripod, actually to insert the RA axis back into the lower section of the mount I found it easier to take a different approach.  The "middle" bearing on the RA axis can be a bit of a pig, it seems.  In use it sits right next to the upper bearing (which is inside the brass RA gear) and fits into place in the lower section of the mount.  If it goes in anything other than perfectly true however, eventually something ends up binding and it isn't possible to get the mount head into place properly.  So what I ended up doing was sitting the entire RA and DEC assembly on a flat surface so the polar scope cap is down and the RA axis pointing straight up, like this:

The bearing can then be fed onto the RA axis all the way down.  I found it still "grabbed" a bit in places, but rotating the bearing seemed to make that easier.  I assume the RA axis isn't perfectly round.  I then took the lower section off the pier and fed that over the top as well.  This is much easier because it's lighter and it's now possible to see the end of the RA axis as it passes through the mount, so it's possible to keep everything pretty well lined up.  The tapered thrust bearing can then be dropped into place easily followed by the retainer.  With everything done up finger tight it can be returned to the pier/tripod for final reassembly.

I suspect the backlash I was seeing was due to poor engagement of the worm and RA gear ring.  I couldn't see any particularly obvious end float in the worm, certainly.  Now it is significantly reduced, to the point where I'm not sure I could get it any better.

James

[Miguel1983]

Nice job 👌

Did the cleaning and regrease make a noticeable improvement, most people doing this report a major improvement in smoothness.

[JamesF]

On 15/05/2020 at 05:08, Miguel1983 said:

Nice job 👌

Did the cleaning and regrease make a noticeable improvement, most people doing this report a major improvement in smoothness.

Apologies for not replying to this sooner.  I missed it somewhere along the line.  The mount does seem much smoother, but I've had little chance to test it yet.  Not long after I finished it astro darkness disappeared and the weather changed, so I can't claim to have fully tested it yet.  There's always a niggle in the back of my head that I might just perhaps be able to get rid of a tiny bit more of the backlash in the worm gear, too

James

[spillage]

I don't know why but I have a habit of putting the worm and gear into the housing and forgetting to put the belt on and only noticing once I have the worm fully installed.

I found that using a length of strimmer cord works wonders when pulling the belt through into the housing, I guess its the same as an elastic band but will not snap.

If you set the tension on the worms before putting it back together then it may be easier to set the worm and gear using the two grub screws first and get it as close as possible and then making adjustments to the screw on the end of the worm shaft to take that last bit out if needed.

Just my 2p worth.