NEQ6 Belt Mod - Worm Mesh Setting Advice Needed

[IanL]

As a follow up to my previous post on removing some of the bearings, I have now completed the Rowan belt mod on my NEQ6.  I haven't been able to test it in anger yet, but I am not convinced I have got the worm mesh settings sorted out despite several hours of careful effort yesterday.

The main issue (unsurprisingly perhaps) is that I can't find a satisfactory compromise between play in the axes (backlash) and binding when slewing.

The RA axis always had a bit of play in it, but now seems to have considerably more after re-assembly.  The Dec axis used to be pretty snug - no play when trying to rock the axis by hand with the clutch engaged.  It now has a lot of play (similar to the RA axis - maybe as much as a degree - hard to tell but it is a very definite clonk from one side of the mesh to the other, not just a slight wiggle).  I've carefully followed all the online advice I can find, basically the procedure is:

- Start with the mount unloaded.

- Make sure the worm-end float nut is slightly lose to start.

- Slightly loosen the four large bolts on the worm carrier.

- Slacken off one of the worm mesh adjusters, tighten the other until there is no play in the axis when rocking by hand.

- Slightly loosen the mesh adjuster and tighten the other one.

- Rotate the axis using the motor and tighten the end-float nut until it just binds the worm and then slacken of a bit.

- Now tighten the mesh adjuster until there is slight binding and then back off a bit (less than 1/8th of a turn).

- Tighten down the four large bolts and test through several 360 degree rotations in both directions.

Now this bit all goes great - I can easily enough find a spot with no backlash that I can feel by rocking the axes, and no binding anywhere on the 360 degree rotation.

The problem arises when I load the mount (not a big set-up, just the ED80 plus ST80 piggy back, with two counterweights pushed almost up to the weight bar collar). Balance is pretty good in RA, though maybe the axis feels slightly tight - perhaps need to back off the weight bar collar slightly?  Balance in Dec is a little bit front heavy as I don't have my (small) camera on there, but nothing excessive and wouldn't have thought it a major issue since the rig has always been front heavy.

The issues are:

1. I need to slacken off the RA mesh a bit to avoid any binding, to the point where there is a fair bit of play when rocking the axis manually.  As noted above there always was a bit in RA, but it is now slightly worse than before.

2. Dec is a nightmare.  I get nice smooth rotation on one side of the ring gear, but on the opposite side it is binding a bit (somewhere between a quarter and a half of the rotation on different attempts at the set-up).  It doesn't lock up completely, but as it goes in to that side of the ring gear it starts gently vibrating with a pattern that matches the rotation of the worm itself, and the further it goes round the worse the vibration gets until you can actually see/feel the OTA juddering visibly (not massive but a fraction of a mm in amplitude), and then it passes through the worst point and gradually reduces again until no vibration at all.

If I load the worm by trying to hold the axis back slightly against the direction of rotation the vibration disappears and stays gone after releasing it.  Conversely pushing the Dec axis the other way towards the direction of rotation will induce/make worse the vibration and it tends to stay until it gets round to the other side of the ring gear.

I have managed to set it to a point where there is no vibration all the way round, but this involved slackening the mesh a lot, and when the vibration is at its worst gently tapping the worm carrier with a rubber mallet - this seems to re-seat the carrier slightly, but I might be fooling myself since it could just be forcing the worm on to the other side of the gear temporarily as described just above.

The problem is that there is then a lot of backlash in the Dec axis (which is going to be the problematic one when guiding I guess - RA should be OK once tracking since it doesn't need to reverse).

So any ideas of where to go next - I don't really want to strip everything down again if I can avoid it (took three days on and off).  The belt mod itself looks to be fine - have checked and the belts are properly engaged, not too tight or loose from what I can tell and not rubbing against the sides of the slot in the mount.

I did replace the worm roller bearings with new SKF steel ball ones (not ceramic) and the rest of the main bearings all looked to be fine - plenty of lubrication, no corrosion or signs of damage or other problems.  I also re-lubricated the worms and rings with some PTFE lubricant.  My only thought is that some slightly thicker lubricant might help mask the backlash a bit whilst retaining a looser mesh, but the new lubricant seemed pretty similar in consistency to what was already on there.

All suggestions gratefully received.

[Mukv]

Greetings

I had very similar issues and tracked it back to a critical measurement of 1mm

this in my case was just too tight and I pushed it to 1.75mm and that cured all tight spots in both directions on both axels

also backlash is virtually zero, my mistake was in not reading through enough times because I missed

"19. Temporarily place the 47 tooth pulley on the
worm shaft and check the shaft shoulder is above
the pulley face by 1.0mm or more. Loop a belt
around a 47 tooth pulley and slide the worm back
into position. Gently tighten the 2 grub screws with
longer grub screw against the shaft flat."

the or more bit was what I missed.

it may be worth adjusting / checking.

Andy

 

[IanL]

Greetings

I had very similar issues and tracked it back to a critical measurement of 1mm

47tooth.PNG

this in my case was just too tight and I pushed it to 1.75mm and that cured all tight spots in both directions on both axels

also backlash is virtually zero, my mistake was in not reading through enough times because I missed

"19. Temporarily place the 47 tooth pulley on the

worm shaft and check the shaft shoulder is above

the pulley face by 1.0mm or more. Loop a belt

around a 47 tooth pulley and slide the worm back

into position. Gently tighten the 2 grub screws with

longer grub screw against the shaft flat."

the or more bit was what I missed.

it may be worth adjusting / checking.

Andy

Thanks Andy,  I will take a look see next weekend (or probably thereafter since it's the Mrs birthday!)  I did check the 1mm measurement initially, but I am not convinced that I ensured the pulley was properly in that position after tightening the grub screws.  Does the pulley bind on the worm carrier or some other problem do you know - it would help if I could spot any wear if knew where to look?  I'll try any suggestions that come up not involving disassembly first, but I guess I may have no option in the end.

[Mukv]

Greetings

When slewing with no load there was no problems at all but when even a slight load was applied  even resistance with a slight pressure of a finger it would bind to a point when the belt would jump teeth.

after contacting Dave and re reading through the instructions narrowed it down to this clearance , when slewing in the direction that loads the worm towards the 47 tooth gear it pushes that gear onto the

wall of the mount and then binds, this is where the clearance needed to be adjusted in my case.

Andy

[IanL]

Yes now that makes perfect sense as it was generally binding when the heavy front of the OTA was loading that side of the mount.  I guess it would be really easy to diagnose by slewing Dec until it starts to bind, then slewing the RA to move the load to the other side of the Dec axis and then starting up the Dec slew again.  Bit of a pain to disassemble but it should be easy to fix.

Thanks Andy.

[1parsec]

Hello Ian,

One adjustment you can make before stripping the mount down again is with the bearing retaining rings.

Loosen the ring at the opposite end to the 47T pulley by 1/2 turn and the take up the clearance by tightening the bearing ring at the other end.

This will move the 47T pulley away from the face of the casting.

It could be the bearing at the 47T pulley end is sitting too far inside the casting and allowing the pulley to touch the side wall of the casting even with the correct 1.0mm dimension shown in the photo in the message above. 

Cheers, Dave.

[IanL]

Hello Ian,

One adjustment you can make before stripping the mount down again is with the bearing retaining rings.

Loosen the ring at the opposite end to the 47T pulley by 1/2 turn and the take up the clearance by tightening the bearing ring at the other end.

This will move the 47T pulley away from the face of the casting.

It could be the bearing at the 47T pulley end is sitting too far inside the casting and allowing the pulley to touch the side wall of the casting even with the correct 1.0mm dimension shown in the photo in the message above. 

Cheers, Dave.

Thanks Dave.  As far as I can recall, there is a worm float nut at the end without the pulley (i.e. the slotted nut that you need to use the special tool to adjust).  At the pulley end there is no nut or other means of adjustment - the bearing just slides from the inside of the carrier towards the outside and then stops against the casting at/just before the thread for the black dust cap.  So the only adjustment that I can make is to tighten the float nut to push the non-pulley end bearing inwards, whereas what I need to do is push from the other end to push the pulley away from the side of the casting - can't see a way to do that as you are suggesting?

[1parsec]

Hi Ian,  Yes you're right

I was going from memory and some how had it in my mind there were rings both ends.

It would need a small spacer ring inserting between the cover cap and the bearing at the 47t pulley to make the adjustment I was thinking about.

So providing the bearing at the 47t pulley end is flush with the inside wall of the casting the 1.0mm dimension should be fine. A spacer ring would be needed if not.

Dave.

[r3i]

Not sure if what I experienced when installing the Rowan kit is the same as what you're having but after adjusting the RA worm mesh as best I could, I still kept getting a kind of grinding sound at certain points.  It wasn't the typical stepper motor chatter that you get when the axis fully binds.  I finally traced it to the tension of the pulley belt - by tightening it a bit more than what I had originally the grinding stopped and the mount now runs very smoothly.
 

[IanL]

OK thanks, I'll try some more tests and then maybe tension the belt more - I didn't try to pull it too hard as it was clearly engaged and rotating the motor fine.  It's definitely a grinding sound and appears to be coming from the vicinity of the worm.

[Nathan_Pembs]

Hope you get the belt mod sorted soon

Been looking at the kit for my Heq5, as it sounds like a coffee grinder sometimes during slews lol

Are they meant to be this difficult to install? :/

[r3i]

Are they meant to be this difficult to install? :/

I wouldn't say they are difficult, it just needs a few tweaks here and there.  A lot of people get them installed without any fuss whatsoever.  Definitely worth the effort though.

[1parsec]

Are they meant to be this difficult to install? :/

The HEQ5 is much more straight forward as the mount does not need to be stripped down to the level the EQ6 does.

[IanL]

Hope you get the belt mod sorted soon

Been looking at the kit for my Heq5, as it sounds like a coffee grinder sometimes during slews lol

Are they meant to be this difficult to install? :/

Depends on what you man by 'difficult' I suppose.  I am not completely mechanically inept or I wouldn't have attempted the mod, but nor am I someone who has a lathe and a drill press in the garage.  I have taken my time and run in to a few minor gotcha moments because this is the first time I have stripped down something like this, but nothing a bit of common sense, helpful advice and walking away for 10 minutes to avoid getting frustrated couldn't cure.

I was expecting the mesh adjustment to be tricky as it is probably the one thing most people have written about online, and so it is proving.  There is nothing inherently wrong with the mount and it all went back together as expected, so I just need a bit more time to finesse it.  I guess it all comes down to your level of confidence with this kind of job as to whether it will be easy or hard. It certainly hasn't taken four hours as some have reported (thought they all seem to have stripped their mount at least once before), I spent about three days on the job off and on, but could probably break it all down and put it back together again far more quickly now I know what is what.

[Nathan_Pembs]

Well I modified my dslr, removed the filter, with all the fiddly ribbon cables etc I suppose I could manage it

[Mukv]

Greetings

there is nothing difficult in the whole procedure just need the tools to hand and those are included in the kit, the special tool makes adjustments easier  but it can be done without, I used a pair

of snipe nosed pliers to turn the ring because the tool was just out of sight and I was feeling lazy. paper towels are handy to have close by because of the grease on the bearings.

the only scary part is at the end when you realise how easy it really was.

Andy

[IanL]

Just thought I'd follow up for anyone else who finds this thread whilst looking for help:

- The RA axis/backlash was easily sorted out.  I checked the worm end-float adjuster and it was way too loose - I could see the bearing and end of the worm moving backwards and forwards when I rocked the axis by hand.  I tightened it up to the point where the worm started binding when being driven, slackened a fraction of a turn and it was fine.  Didn't need to re-adjust the worm mesh at all, virtually no backlash/play and no binding anywhere during the rotation.  I'm not sure why I left it so loose in the first place to be honest, must have overlooked it when I was having Dec problems.  Anyway it it is better than it was originally in terms of play and no binding or odd sounds during rotation.

- The Dec axis was a bit harder, but I think I have got it sorted out without any need for further disassembly:

- The first thing I noticed was when I pushed downwards on the Dec axis during rotation (at the dovetail clamp end) was that the worm started making a lot of noise.  I tightened up the weight collar a lot more to see if I could take that element play out of the axis. This was successful - the collar is a bit tighter than I would really like to the point that when the clutch is unlocked it doesn't rotate completely freely - easy to move by hand and doesn't cause any problems for the motor, but definitely tighter than one might consider ideal.

- Next I loosened everything off (end float, four main screws, mesh adjuster).  I then pushed the worm carrier up so the worm and ring gear were mated and tried to make sure the carrier and the mount body were as square as possible along the two long edges, and then tightened up the mesh adjusters and main screws to hold it in that position before backing of the mesh a bit.

- I then tightened the worm end float to the point whilst rocking the Dec axis to the point where there was no visible movement of the bearing or end of the worm.  (This later turned out to be nearly perfect in terms of not binding the worm).

- Then I gradually adjusted the worm mesh to find the tightest point I could with no binding and the least amount of grinding sound, before tightening up the main bolts fully.

- I eventually found a point where there is absolutely no backlash/play in the Dec axis that I can feel.  There is no sound of the worm on the ring gear slewing in one direction.  There is still a slight vibration/rubbing sound when going the other way at certain points/orientations of the OTA, but they can only be heard if I press my ear against the mount body and listen carefully.  It's a much reduced version of the same noise I had in the original post so I'm still not sure if this is OK or a problem.  It's a bit hard to tell whether this is just 'normal' for this mount or not - bear in mind that this sound would have been drowned out by the transfer gear noises prior to the belt mod and I've never put my ear on the mount to listen either!

I haven't had time to test at lower speeds yet - it is fine at full speed but I guess if there is some binding then it might stick or be more jerky at lower slew rates or guiding rates which would clearly be a problem!

Next up I need some clear weather at the weekend to test the thing in anger.  Unfortunately this isn't looking likely, given the situation the railway station car-park this morning!