NEQ6 Mount rocking - is this normal?

[newbie alert]

24 minutes ago, Stuart1971 said:

Do you know the actual locking nut we are discussing, and how thin the threads are...? Yes I agree on a normal bolt or grub screw....but on this occasion I have to respectfully disagree... 👍

I presumed you was talking about a grub screw, but if you can get abit of hot melt on it, then I'm sure a tiny bit of threadlock is far easier than hotmelt 

But please, enlighten me

[JamesF]

I have an NEQ6 that behaves similarly.  I plan to do a belt upgrade shortly, so I was hoping I could get most of it sorted then.

Personally I'm not sure it's the worm engagement though it's entirely possible I'm wrong.  I think I'd prefer to have it in pieces and check the RA worm from the ground up, as it were.  It's a bit of a concern that the screws are so tight though.

James

[spillage]

Hi

This looks just backlash on the mount. Did you do the belt mod yourself?

I would loosen off the four nuts on the RA worm housing. You need to slacken off the top grub screw and wind out the bottom screw 1/4 turn at a time. Tighten nip up at least three of the four bolts and then move the mount in RA and check for binding. I would continue doing this until the mount binds and then slowly take the bottom grub screw in until the binding stops. If you then still have some backlash then tighten up the worm (make sure the black cap on the other side of the control panel is done up tight first then wind in the opposite side and this should remove any remaining play.

Hope this is some help?

[CraigT82]

My EQ6 did exactly the same, as in you're video. Had to tighten the slotted nut on the worm end shaft. The one under the round black cap on the control board side.  But seems like you've already done this so prob not much help, sorry! 

[newbie alert]

19 hours ago, newbie alert said:

I presumed you was talking about a grub screw, but if you can get abit of hot melt on it, then I'm sure a tiny bit of threadlock is far easier than hotmelt 

But please, enlighten me

Maybe I stopped reading abit too soon, as soon as you mentioned superglue( which is a bodge) and then counterstated that it was hot melt( which also won't work on the part I now know what you're talking about)  use the right tools and methods on components and the job is far easier and quicker and won't need to be redone again..

Take it's this part, with the correct tool?

Yes it needs threadlock, hot melt just won't last or do the job properly 

[JamesF]

I've now completed the belt mod on my NEQ6 and I have very much the same problem as Luke.

The thing is, I could actually reduce the backlash quite significantly, but for three or four spots all in the same quadrant of the RA gear that cause a brief jump of the motor.

I am thinking that it may well be possible (particularly since the mount is permanently on a pier) to shift the position of the RA gear so those tight spots are all on part of the gear that is never used.  For instance, it is unlikely that the mount will ever need to move from having the counterweights due west to them being just beyond due east having travelled via north.  Unless I'm missing something obvious (which may well be the case) that means that generally only perhaps 190 to 200 degrees of the RA gear is actually ever used.  If I could arrange for the tight spots on the RA gear to be outside of that range then I could probably get a better mesh elsewhere and reduce the backlash.

Or am I confused?

For what it's worth I think my problem (and quite probably Luke's too) is specifically related to the worm/RA gear engagement.  I don't think it's end float in the worm, but I think I may be able to test mine by removing one of the worm end caps and checking with a dial gauge to see if the worm is moving laterally.  It may even be possible to feel it by hand.

James

[tooth_dr]

It looks like what @spillage is describing.  The big brass cog isn’t engaging the worm gear.  I’ve had my EQ6 stripped a few times and followed Astro baby’s guide. Common sense will help you where there is some overzealous advice re over-tightening stuff.  I just used it to see what bits need to come off and be loosened

[JamesF]

Oh, I agree.  The problem in my instance is that if I increase the engagement any further at all then there will be places where the RA axis binds slightly.  If I can arrange for those spots to be in a place that will never be used then I could increase the engagement quite significantly I think.

James

[alacant]

On 04/05/2020 at 19:38, JamesF said:

not sure it's the worm engagement

Hi

When you reassembled, are you sure that you had the curve of the worm centralised on the curve of the brass gear teeth? I needed quite a bit more than the original teflon washers offered. See the material used to obtain the correct distance. And no laughing;)

This shows the south washer. The North -on the other side of the brass gear- is however the crucial one. On my mount, it was the same thickness of material that was used.

HTH

 

 

 

Edited May 10, 2020 by alacant

[JamesF]

Hmmm.  I'll look into that...

James

[spillage]

For what it is worth, I have spent a long time trying to get the best out of my mount. The reality is that the components are not 100% and there are manufacturing discrepancies.

I will admit to having DEC backlash and I am sure something is loose (sure its the cog on the worm shaft). My RA is as close as it will ever be so this has now been left alone. I only use the 130pds with a st80 strapped to it so not much weight there but still will get around 0.6-0.8" rms (I have even seen sub 0.5" on occasion) in total.

I think what I am trying to say is just run the mount see how it performs. If you not that happy make very small adjustments and run it again. Also I find equal balance very important with the belt mod.

[sloz1664]

3 hours ago, alacant said:

Hi

When you reassembled, are you sure that you had the curve of the worm centralised on the curve of the brass gear teeth? I needed quite a bit more than the original teflon washers offered. See the material used to obtain the correct distance. And no laughing;)

This shows the south washer. The North -on the other side of the brass gear- is however the crucial one. On my mount, it was the same thickness of material that was used.

HTH

 

 

 

All the calculations for centralising the worm gear to the brave drive ring are in Astrobaby's EQ6 stripdown & rebuild posts. Regarding the "over tightening" technique on tapered bearings. This is a tried and tested method to ensure all the components are fully" bedded in" to enable the assemble to work effectively. If you have ever adjusted the wheel bearings on your car you would use the same technique. As for damaging the components, they are hardened steel and the force required to damage them would far exceed what is necessary to "bed  them in"

Steve 

[newbie alert]

11 hours ago, JamesF said:

The thing is, I could actually reduce the backlash quite significantly, but for three or four spots all in the same quadrant of the RA gear that cause a brief jump of the motor

This could be a number of things, cranking down on the clutch levers pushes the ring gear out of line.. over tightening the locking nut on the shaft where the taper bearings are can squeeze  everything up and cause the worm not to line up with the ring gear teeth .. lateral play in the worm spindle( with this you won't be able to ever get rid of acceptable backlash..

[lukebl]

Well, I'm chuffed to bits that, after dismantling the whole mount and reassembling it, it now appears to be functioning properly again and running smoothly.

The original problem appears to have simply been a loose worm locking ring as suggested by Stuart1971 and others, exacerbated by me messing around with the grub screws and damaging some threads and generally being cack-handed. Now that I'm less intimidated by the interior mechanism of the mount, I'd be confident to undertake the Rowan mod on my other NEQ6 myself.

It does appear to have been a creeping problem which I'd failed to notice, and explains a lot of the guiding issues I'd been having. In particular, it explains a curious satellite trail on this image which I posted a while back. I think it was simply caused by the RA drive rocking back and forth, and not by an oddly tumbling satellite. It would also clearly result in a lack of sharpness in long exposure images.

[JamesF]

Well, if it's that simple to fix I shall get out and play with mine forthwith :D  Perhaps I just was over-cautious about doing up the RA worm locking ring.

Pleased to hear that you've sorted it.  As I said in my PM, the scary thing about the whole process of doing the belt mod is actually the idea of taking almost the entire mount apart in the first place.  It's really not that complicated a process once you get into it as long as you're patient and methodical (which are probably defining qualities for astro-imagers :)

Some of the online videos show heat being applied to parts and all sorts, but I didn't have to do any of that.  The grub screws holding the gear on the end of the worm were certainly tight and my allen key did flex a bit before they started to turn, but at no point was there any need to get medieval on anything.  I also have a second mount to do, so once I have this one sorted I'll be finding out if that is the same...

James

[JamesF]

Well I just had to go out and tinker with my NEQ6 this evening.  I ended up disassembling most of the RA axis in the end, just so I could rebuild it from the ground up.  I now have it working pretty well.  There's clearly a little backlash still there at the moment, but it's so small that I can't actually see it.  I may be able to do better yet.  I suspect in my case it was more the engagement of the worm and RA gear that was the trouble rather than the worm end float.

James

[lukebl]

Having thought I'd fixed everything. how wrong I was!

Guiding is terrible. Something strange going on in DEC. Any ideas? Balance seems good and I can't detect any significant backlash.

This is using an Off Axis Guider and a 1624mm Focal length.

 

[alacant]

45 minutes ago, lukebl said:

Something strange

My guess would be that you've tightened the worm mesh too much and now it's sticking, but without seeing the logs, it's only a guess. 

Not sure the scale of the graph is correct... How do the images look?

Cheers and HTH

 

Edited May 16, 2020 by alacant

[lukebl]

3 minutes ago, alacant said:

My guess would be that you've tightened the worm mesh too much and now it's sticking, but without seeing the logs, it's only a guess. 

Not sure the scale of the graph is correct... How do the images look?

Cheers and HTH

 

Thanks. The images are terrible!