Poorly HEQ5 - previous owner syndrome!

[chrisund123]

I've got a 2nd hand HEQ5 Pro, and it has some issues guiding in Dec. PHD2 guiding assistant failed to make south moves in Dec, so I tried to adjust the backlash, only to find it wasn't possible... Something was amiss. Felt like one of the grub screws was just turning... Damn.

Out with the tools then ready for a strip down. Full disclosure, when I picked up the mount the previous owner did point out it had a repair at some point in its life. Not to be put off (HEQ5's are like hen's teeth right now) I figured that I'd be able to fix things up later on if required. All I was interested in at the time was visual and a bit of planetary imaging so the tracking wasn't too important.

Fast forward 6 months and the planets aren't exactly good viewing right now, so I thought I'd get into DSO's...

 

The counterweight cover was held on with these oversized grub screws and the old holes filled in... Curious.

 

Removing the cover revealed a round nut holding in the Dec shaft, in turn held in by grub screws. Pretty sure astrobaby's guide didn't have this...

 

And with that removed, we can see a mangled thread with a blank area for the grub screws to tighten onto. Not good...

 

Then onto the worm gear housing - indeed the thread is stripped in one of the adjustment holes...

 

And to top it off the gear had a rounded off grub screw, so I had to drill it out. I hate drilling out screws, I always end up with bad result and this was no exception...

 

Anyway that got the Dec axis stripped down. I'm hoping that I can do the following:

 

1) Tap a new thread in the worm gear housing. The hole is a bit close to the edge, but hopefully it will be OK.

2) Run a die over the thread of the Dec shaft. I measured it at M24 X 1, and funnily enough I don't have that size in my tool box(!). I've ordered a die from China, so will be in for a bit of a wait. Despite its unwelcome presence, I think the previous repair ought to be sound if the damaged threads can be made "good enough" to get the nut back on.

3) Drill and tap a new hole in the gear. Shouldn't be too difficult now it's off the shaft.

 

And then re-assemble and hope I can tune out the problematic backlash that led me to this hell-scape of bodged repairs!

 

If it goes a bit wrong, anyone got an HEQ5 for spares or repair? I think I may be in the market for some parts...

[Soligor Rob]

Well you have yourself a task to sort, Drilling out bolts/screws etc is easy enough as long as you don't go with too big a drill, also important to have a decent pillar drill and sharp drill bits, then using easy outs to extract the broken part, setting up is 90% of the job.

As for the damaged thread on the shaft, phew that has been brutalised, you might get away with running a die down the thread, if not you could build up the end of the shaft with the help of a friendly welder then turn down to correct diameter in a lathe and then recut the thread and grub screw landing.

I wish you Good luck

[1parsec]

Another way to 'fix' a damaged thread is to use a thread file.  

https://www.ebay.co.uk/itm/Sykes-Pickavant-Metric-Thread-Restorer-File-01560200/174655192797?epid=1310959088&hash=item28aa42bedd:g:ipwAAOSwYcJgOUTz

I've used these on various jobs to good effect when a die isn't available.  

 

[chrisund123]

1 hour ago, Soligor Rob said:

Well you have yourself a task to sort, Drilling out bolts/screws etc is easy enough as long as you don't go with too big a drill, also important to have a decent pillar drill and sharp drill bits, then using easy outs to extract the broken part, setting up is 90% of the job.

As for the damaged thread on the shaft, phew that has been brutalised, you might get away with running a die down the thread, if not you could build up the end of the shaft with the help of a friendly welder then turn down to correct diameter in a lathe and then recut the thread and grub screw landing.

I wish you Good luck

I did drill out the grub screw in my pillar drill, but the problem was I didn't have a great way of holding the workpiece and it kept moving - hence why it looks like I was digging it out with a pickaxe! However now the gear is removed I can drill the replacement hole with the gear held securely in a vice, so I'm confident that part will go a lot better.

I do have some options for fixing up the shaft, if the die doesn't do the trick I think I could get the threads turned down and then get the shaft sleeved, then new threads cut on it. That would require removing the shaft from the top housing though, and as with Astrobaby's guide mine seems firmly stuck in place. I'm yet to see anyone successfully remove the shaft from the housing so I'm hoping I can fix it in situ.

I may treat the Dec axis to some new bearings while it have it all in bits, if ever there was a good time to tune it up...

[Soligor Rob]

If you can't or don't want to remove the shaft then I'm sure a die nut run down the thread and then rebuilt with a dab of  blue loctite will hold all secure.

New bearings is always a good option.

[michael8554]

Horror story !

Readers of a nervous disposition look away now !

Michael

[malc-c]

It's probably an optical illusion, but in that image above it looks like the worm is bent too !

Good luck with the repairs.  It would be interesting to see how you get on so keep us updated

[chrisund123]

On with the repairs!

The hole in the worm gear housing was too stripped for M4, so I got out the 4.2mm drill bit and went straight in at M5. A quick run through with the taps cut a decent thread, and it should be good to go. I've ordered a longer M5 grub screw for this, in an effort to keep more threads engaged when adjusting the backlash and make sure this doesn't happen again. Not that I'm one to strip threads, but maybe there will be another owner in the future!

So that's the problem that forced me to take it apart in the first place all sorted. Now just for the rest of it...

[chrisund123]

One problem down, two to go - now to fix the gear that I knackered when drilling out the grub screw!

With the gear securely held in a vice now it was removed from the worm gear housing, this was a piece of cake. Drilled to 3.5mm (should have been 3.3mm but I don't have that size and couldn't be bothered to buy one), then tapped to M4. Result looks ok to me and should hold the gear on the shaft as securely as ever.

All that remains now is to sort out that abomination of the Dec shaft. The tap and die to do that are on their way on a slow boat from China no doubt, so I will have to wait for that to be doctored...

Wonder what horrors I'll find on the RA axis? No, no, mustn't tempt fate... If it ain't broke, don't fix it! 😂

[Soligor Rob]

Excellent work, hopefully you will have similar success with the thread on the shaft.

[chrisund123]

I had bit of a brainwave on my way to work this morning - I wonder if I'm overthinking the repair of the shaft a little too much?

On a not-FUBAR mount, the counterweight collar isn't typicaly done up tight on the shaft. It's just tightened up hand tight and the backed off until the counterwieight bar locking lever is nicely positioned in line with the dec lock lever, then the grub screws hold it in place.

To me this implies that the counterweight collar just loosely holds the taper bearing in place. With that in mind, I'd go so far as to say it matters very little if the threads are knackered on my dec shaft, and I could in theory 3D print a collar to hold the tapered bearing in place, held in place on the shaft with some grub screws. It doesn't actually need to screw onto the dec shaft, and then the counterweight housing just needs to cover the end of the dec shaft.

I shall perservere with trying to sort out the damaged threads enough for re-assembly, as I'd like my mount to be held together by metal rather than UV cured resin if at all possible, but if the threads don't come up well enough it gives me another option than having to take it to a machine shop for further surgery.

[chrisund123]

Well I've committed to fixing this HEQ5 one way or another - £100(!) worth of new, high quality bearings to go into it.

I keep having to remind myself of the reason why I started messing around with it in the first place - poor Dec backlash. I'm hoping that re-cutting the threads in the adjustment screw will be all that needs, but I do wonder why the thread had been stripped in the first place. Someone obviously felt the need to tighten it way more than was sensible, so I wonder if there was (is?) some underlying issue with Dec backlash...

[Jonny_H]

On 14/03/2021 at 11:51, chrisund123 said:

Well I've committed to fixing this HEQ5 one way or another - £100(!) worth of new, high quality bearings to go into it.

I keep having to remind myself of the reason why I started messing around with it in the first place - poor Dec backlash. I'm hoping that re-cutting the threads in the adjustment screw will be all that needs, but I do wonder why the thread had been stripped in the first place. Someone obviously felt the need to tighten it way more than was sensible, so I wonder if there was (is?) some underlying issue with Dec backlash...

How are you getting on with this? I've been waiting for more photo updates! 🙂

[chrisund123]

On 25/03/2021 at 20:39, Jonny_H said:

How are you getting on with this? I've been waiting for more photo updates! 🙂

Whoops, forgot I'd made this thread!

 

No more pics, but I do have it all back together at last. Tap and die from China arrived, and I was able to repair the threads enough to get the dec axis back together. That coupled with the new thread in the dec worm adjustment has made things much better. PHD2 guiding assistant says I have 400ms of dec backlash now (not sure how much is too much? It was a lot more beforehand!), and I no longer get messages about "unable to make corrections in dec". So I'm calling it a success.

 

However all is not 100% yet - the RA axis has the odd tight spot, I've backed off the worm engagement to make things move free all the way around, but this obviously introduces extra play which is far from desireable. But i don't think this is much of an issue as the RA axis is pretty much always moving in one direction, if it wants to make a correction all it needs to do is move more, or stop moving - not move backwards... In any case I'll let it all bed in for a bit and then see if I can have another go at adjusting the worm engagement on both axis!

 

I've had a few clear nights but I've not done any serious attempts at guiding as I was trying to image the ISS. I'll report back when I've put things through their paces a bit more! I think M81 and M82 are in a good position from my back garden now, Orion has dived behind my neighbour's tree while my mount has been in bits