GEM Az Fine Adjuster

[Shelster1973]

Does anyone know of any plans or designs for swapping the existing Az adjustment bolts with their silly big thread for a finer adjustment option?

Suppose I could tap out the threaded holes that are already there, but where can you find suitably large bolts with a very fine thread?

[ChrisLX200]

If the thread is into some sort of soft alloy then you need to have a coarse thread or it will strip - there's no strength in the metal. If you want a finer thread then use an inserted threaded bush made of stronger material (steel or bronze) then you can choose a metric fine thread (or whatever...).

ChrisH

[Shelster1973]

Just been looking around in tintyweb (yep its a friday near home o'clock time) and came across this place.

Am now thinking, as Chris said, bushing the holes that are ther and fitting 1/4" threaded adjusters to it.  That should be fine enough shouldn't it?  Have gone for that particualr thread as they are the longest threaded adjustters I can find on there.  May need to increase the size of the adjustment peg on the adaptor plate too.....

[Shelster1973]

Just to follow this up.....have actually now swapped out the standard Az bolts with 2 of the fine adjusters and bushes and they work like a dream.

Have just spent tonight getting my mount back on and PA'd and managed to get the following from PHD2 which is the best I have had since I started this 

Seeing was not that great for me tonight and also need to do a full collimation as changed the spider a few weeks back and have not had a chance to do it.

Feel a bit gutted I have not had a chance to image tonight, but with very limited dark time and also having a few more things to tune, am not going to die in a ditch over it

@Peje

[Peje]

Excellent work Paul, lovely graph. You have inspired me to look into this so I can get my PA really tight.

Have you got SGP running? I've been battering away at it over the last week. Got plate solving working and now trying to diagnose a bug in the PHD part.

[Shelster1973]

Cheers Pete

Had tyo drill out the exisiting threads to get the bushes to fit.  Used an 8.4mm drill bit( I think), which was fractionally undersize by .02 mm.  Made a nice snug fit for the bush but secured it with a bit of metal epoxy, so will not come free.

Also greased up the top of the adaptor plate and bottom surfaces of the mount to ease in the turning.  Was very quick and easy to do...although it did take a few turns as the adjusters advance 1/100th an inch per revolution....

[Peje]

Oh drilling threads...I'm less enthusiastic about permanent mods on my newish mount lol

Clearly I'm not man enough!!

[ChrisEll]

On 5/24/2016 at 23:55, Shelster1973 said:

Just to follow this up.....have actually now swapped out the standard Az bolts with 2 of the fine adjusters and bushes and they work like a dream.

Have just spent tonight getting my mount back on and PA'd and managed to get the following from PHD2 which is the best I have had since I started this 

Seeing was not that great for me tonight and also need to do a full collimation as changed the spider a few weeks back and have not had a chance to do it.

Feel a bit gutted I have not had a chance to image tonight, but with very limited dark time and also having a few more things to tune, am not going to die in a ditch over it

@Peje

Wow! 0.5" RMS with an AVX mount and 8x50 guidescope + QHY5L-II? Do you get this kind of performance regularly or was this exceptional seeing?

[Shelster1973]

6 hours ago, ChrisEll said:

Wow! 0.5" RMS with an AVX mount and 8x50 guidescope + QHY5L-II? Do you get this kind of performance regularly or was this exceptional seeing?

I think it was a pure fluke that it was that good that night.

Do not know what it is like now as have had the mount apart and not had a chance to get it back up and running due to all the pump weather we are having.

Have just bought a Polemaster, so next clear night will be out and setting it back up again.

Fingers crossed, it will all work OK and can get back to doing some imaging again

[ChrisEll]

I've been reading about your fixes to your AVX, what else have you done to it since?

I loosened the tension rings in RA and Dec axes on mine, the RA was way too tight. Also adjusted the worm gears' play. These mounts aren't terribly well put together... bit worrying to find some bolts weren't tightened properly and others too tight.

[Shelster1973]

Haven't done anything since I did the polishing to the worms.  Have only put it back onto the pier and then a wee bit of adjusting to the worm housings to get them seated and meshed correctly.

Once I have got it back PA's plan is to measure the PE on it and then correct for that, but lord knows when that one will be.

They are a bit hit and miss in the QA department the AVXs.

I have been contemplating doing a belt mod, but that involves a fair bit of faffing around with rewiring the motors as you have to have them turn in the opposite direction.

 

Also...welcome to SGL too 

[ChrisEll]

>Also...welcome to SGL too

Thanks

How did you polish the worm? I'm always looking for another excuse to take the mount apart

I've noticed that a tight RA worm on the ring gear will accentuate the PE. Originally my RA axis was so tight I could not turn the worm spur gear by hand. When I loosened the axis and adjusted the worm so that I could rotate it smoothly with my thumb the PE dropped off from a max of 30" down to 20". I have since readjusted the worm housing (the bottom two bolts were completely loose so I have fixed that now - the worm probably wasn't sitting square to the ring gear) and I need to re-measure the PE. A bit of play in the RA department is not a bad thing... smoothness is the key thing there as the RA motor only guides in one direction so backlash is not an issue.

As for a belt-mod, from what I've read it won't make much difference on the AVX. Someone on CN tried it once. The main problem with the AVX motor is the gearbox which houses 4 pairs of cogs, that's backlash that can't be cured.

BTW just curious why you opted for a Polemaster when there's Sharpcap.

[Shelster1973]

The polishing was done with a wool mop on a polisher and some jewellers rouge. Didn't take much effort and came out quite shiny 

The over tight worm housing was something I had on the rebuild. I was able to move the gear by hand but it caused some bad jumps and starts when skewing. Managed to get it sorted though

Went with the polemaster as I can use it to do a quick check at the start of a session and it means I do not have to mess about with my guide set up

[Anthony RS]

On 17/01/2018 at 21:31, Shelster1973 said:

The polishing was done with a wool mop on a polisher and some jewellers rouge. Didn't take much effort and came out quite shiny 

The over tight worm housing was something I had on the rebuild. I was able to move the gear by hand but it caused some bad jumps and starts when skewing. Managed to get it sorted though

Went with the polemaster as I can use it to do a quick check at the start of a session and it means I do not have to mess about with my guide set up

I'm really sorry for trying to revive an old thread but I really need your help. I've stripped down my avx, cleaned and replaced the bearings but I'm having a hard time adjusting everything optimally. Basically I'm having a lot of side to side free play in the RA axis no matter how much I tension the worm shaft, worm to ring gear, and the motor to spurt gear.  I tightened eveything till the motor binded and still had a lot of slop. The result is my guiding has huge peaks every minute or so which I think is because of the free play, not sure though. Did you have any of these issues and do you think the peaks might be due to the slop or smthing else like tightening everything too much or vice versa? Also how can i tell if the worm gear is not tilted and is sitting right at the center of the ring gear? It seems impossible to tell.

Appreciate any help!

Anthony.

[Shelster1973]

Anthony

Sent you a reply to your PM.

You are right, it is nigh on impossible to tell if the worm is sitting correctly.  I only ever managed it through feel of the way the whole thing turned and also trial and error.  It is a very fine balancing act with all 4 bolts that hold the worm in place, along with the adjuster grub screw to get the whole ting done correctly.  Before my AVX died (may it track true on the great pier in the sky) I also had the excessive wobble you mention.  I contemplated using a mild thread lock glue towards the end to stop the bolts backing out when the mount was in use, but things got a point where I was better off cutting my losses and retiring the mount, which I did.

Keep asking and am sure people on here will be able to help out with more advice.  As you can see, was well over a year ago that I went through this, so there should now be more experience out there