Possible improvements to NEQ6 mounting on pier and PA adjustments.

[Gina]

I've been looking into possible alterations to the mounting of my NEQ6 on my pier mainly with the idea of improving a couple of things, particularly the PA adjustments. The azimuth is not too bad but the altitude is a problem particularly now with the extra weight on the mount from the MN190 and two wieghts. It wasn't too bad with the ED80, ST80 and wide field imaging rig with just one weight. I guess the mount now has about twice the weight on it that it had before. The problem with the NEQ6 design is that the length of lever used in the adjustment in altitude is too short and there's too much friction on the screw threads (and where it contacts the lever). I think I could do with taking the mount off and having a good look at it to see if I can work out something better.

The other thing was size of pier adapter plates. When doing an unattended imaging run a while back the DSO passed the meridian and continued it's tracking westward until the bottom of the scope collided with the pier adapter plates. So I wondered if I could improve things by using smaller plates. Well, I checked this out this morning and while smaller plates would allow slightly longer time the propper solution will be to stop the scope going too far past the meridian because a collision is possible however small the pier mounting is. This only happens in some cases where the object goes past or very close to the zenith otherwise the system is quite happy to go way past the meridian.

Here is a diagram and photo of my present mounting which uses a SkyWatcher NEQ6 pier extender to increase the pier height. With the ED80 etc. this lifted the scopes above the pier adapter plates and I never had a collision problem but the MN190 comes down lower. The extender also helps with the amount of room around the PA adjusters but the altitude adjustment is still far too stiff and difficult. I really need to take the mount off the pier extender and have a good look to see if there's anything I can do to improve things. I'll report any progress.

[swag72]

To stop collisions, have you set limits in EQMOD? Can't offer any thoughts on the other bit!!

[Spikey]

Beaten to it by Sara I was also going to suggest setting limits in EQMOD or parking the scope at a predefined time.

[Gina]

Thank you both No I haven't set EQMOD limits as yet - must look into that

[Zakalwe]

You could either modify the point where the bolt pushes against the mount so the bolt is pushing against something better than a sloping piece of aluminium. Perhaps a piece of steel with a "dimple" in it could be machined up and bolted to the casting. Or you could get a piece machined up that holds the rear bolt at an angle so it meets the casting at a right-angle?

Though, to be honest, that'd make more sense on a tripod where you constantly need to PA. Surely on a pier its a matter of polar-aligning and then forgetting about it?

[JamesF]

I have thought about fixing the mount to a mounting ring that is not horizontal. For example, if the mounting ring were inclined at thirty degrees towards the north then the mount would only need to be in the position it would normally have for about twenty degrees latitude (for you and me, at least). The rear alt adjustment bolt would then bear on the adjustment cam much more squarely, reducing the sideways load on the bolt and making it easier to turn.

James

[Gina]

You could either modify the point where the bolt pushes against the mount so the bolt is pushing against something better than a sloping piece of aluminium. Perhaps a piece of steel with a "dimple" in it could be machined up and bolted to the casting. Or you could get a piece machined up that holds the rear bolt at an angle so it meets the casting at a right-angle?

Yes, I was thinking of something like that as a possibility or maybe a wedge glued onto the lever inside the mount to change the pressure angle. Another idea was to use the Synta adjuster as coarse and arrange a slighly rocking mounting plate for fine adjustment.

Though, to be honest, that'd make more sense on a tripod where you constantly need to PA. Surely on a pier its a matter of polar-aligning and then forgetting about it?

Well, yes, but I haven't managed to get the altitude right yet. I don't seem to be able to get consistency - I think it "setles" after adjustment and then changes by several tens of moa. From tests it seems PA needs to be well better than one minute of arc to stay on target with tracking only for more than a minute. Something I can get nearly right and then leave (or fix) would be fine. I guess my guiding is mostly overcoming the PA deficiency but I would like to get it better.

[Gina]

I have thought about fixing the mount to a mounting ring that is not horizontal. For example, if the mounting ring were inclined at thirty degrees towards the north then the mount would only need to be in the position it would normally have for about twenty degrees latitude (for you and me, at least). The rear alt adjustment bolt would then bear on the adjustment cam much more squarely, reducing the sideways load on the bolt and making it easier to turn.

James

Yes, I wondered about something like that too but I don't think I could manage it.

[Zakalwe]

The angle that the bolt makes with the central casting is fairly acute. It hink that what happens is that the bolt deflects slightly because of the angle and the amount of thread inside the mount. That deflection would act like a spring which might account for some slop...that'd make it difficult to get a find adjustment.

I've not dismantled my mount, but I would assume that it'd be possible to machine a large ally "wedge" that could be bolted to the main casting. That'd mean that you'd only need, say, 12-15mm of thread inside the mount before it'd hit the wedge? The bolt would then be at a right angle, plus there'd be no long bolt to deflect.

[JamesF]

Hmmm. It does look a bit more tricky with the pier extension in place. Otherwise I'd probably have replaced your spacing washers with slanted sleeves above and below the top plate to hold the plate at an angle whilst allowing the bolts to remain vertical.

James

[Zakalwe]

Final modified EQ6 RA assembly by Mickut, on Flickr

Here's an idea that I found on Flicker.

[JamesF]

I've not dismantled my mount, but I would assume that it'd be possible to machine a large ally "wedge" that could be bolted to the main casting. That'd mean that you'd only need, say, 12-15mm of thread inside the mount before it'd hit the wedge? The bolt would then be at a right angle, plus there'd be no long bolt to deflect.

The entire design is fairly poor for UK latitudes, really. There's a cam with a triangular lobe sticking downwards from the alt axis. The front and rear bolts bear on the lobe to locate it and hold it in place. When the alt axis is at UK-type latitudes the lobe is sufficiently far forward that a fair proportion of the load on the bolt once the OTA is mounted is downwards rather than along its length. The material used for the standard bolts is sufficiently soft that the load can cause them to bend. Replacing them with stiffer ones as is common practice does usually resolve the problem, but at the cost of increased load on the threaded section of the mount body (made of fairly soft aluminium) through which the bolt passes.

James

[JamesF]

Here's an idea that I found on Flicker.

Basically making a second lobe further back. That's not such a bad idea -- something that's relatively straightforward to do given access to a drill press and some taps.

James

[Zakalwe]

Thnink laterally, there's another very simple "fix" (or bodge!). Use the "levelling" plates that are on top of the pier to tilt the pier extension back off vertical. The mount altitude would then have to be changed which would reduce the amount of bolt inside the mount and also lessen the angle that the bolt is operating at. You might need to elongate the holes in the plates to get sufficient play in them.

[JamesF]

Thnink laterally, there's another very simple "fix" (or bodge!). Use the "levelling" plates that are on top of the pier to tilt the pier extension back off vertical. The mount altitude would then have to be changed which would reduce the amount of bolt inside the mount and also lessen the angle that the bolt is operating at. You might need to elongate the holes in the plates to get sufficient play in them.

See post #6

James

[Zakalwe]

See post #6

James

Yep....same thing really. Anyone with "levelling" plates has the kit necessary to do this. plus it'd have the added benefit of moving the scope away from the pier when pointing at the zenith.

[Gina]

Thank you both

I've been Googling and browsing other threads on here and pretty much have the gen now

This is the thread that describes the metal wedge attached to the lever/lug :- http://stargazerslounge.com/topic/164290-neq6-tight-latitude-adjustment/

And a more refined engineering solution :- http://stargazerslounge.com/topic/161907-neq6-tuning-kit/#entry1635804

But a simpler solution without using any additionat bits of metal that would be very quick and quite adequate I think for a pier mounted mount ( ) which is only going to be set once and left :-

http://www.alphageek.co.uk/page21.html

[Gina]

Friction could be reduced with a thrust bearing for the tip of the bolt but I think there would be more friction from the thread. Anyway the phrase "using a sledge hammer to crack a nut comes to mind" Some molybdenum disulphide grease on the thread would also reduce friction.

[JamesF]

I added a thrust bearing for my EQ3-2. It's an endcap for 10mm copper tube that I happened to have lying about

James

[Gina]

I added a thrust bearing for my EQ3-2. It's an endcap for 10mm copper tube that I happened to have lying about

James

Ah yes. I was thinking in terms of a ball bearing

[Gina]

I'll check to see if we've already got some moly grease and if not I think I'll buy a tin. Has lots of uses where a high pressure low friction joint is required. I can use it on the azimuth bolts too and would probably be a good idea on the main mount bearing surface where it turns for az PA adjustment. Anything that makes the adjustment easier and smoother must be good

Just wondering if it would be good on adapter threads - I've read that it's good to stop "cold welding" of threads.

[Tinker1947]

This stuff stops thing seizing ect, Halford ect will have some in stock......

http://www.commaoil.co.uk/productsguide/view/6/220

[Gina]

I've taken the MN190 off the mount, taken the mount off the pier extension and brought the mount indoors to work on. I've found out why I couldn't get the altitude adjustment to work properly! Took the plates off the sides (with hammer and screwdriver) and then attacked the grub screws with a 2.5mm allen key as mentioned in one of the posts. I nearly broke the allen key getting them undone!! Good job they're a high quality set Then used a ring spanner to undo the bolt and took the mount apart. There's a pronounced gouge where the up bolt has chewed into the aluminium lug! Said it was tight

[Gina]

A couple of photos - the gouge in the lug made be the adjuster bolt and the dents in the steel washer where the allen grub screws bit into it - they were THAT tight!

I'll drill the lug to give the bolt a square-ish surface to press onto anyway I think but the real improvement will be from having the grub screws just tight enough and not screwed in by King-Kong!!

[JamesF]

My EQ3-2 has a similar gouge, but even worse. I thought I had some photos somewhere, but I can't find them at the moment.

James