HEQ5 recon & tune

[MishMich]

I decided to bite the bullet. Another cloudy night, Still waiting for the 240->12v power converter; the mount complaining whenever I loaded up the SPX, the power pack's mysterious intermittent discharge. I had read through Astro-Babe's instructions a couple of times (enough to put me off!), but a discussion with Steve at FLO, a couple of evenings left to my own devices without clear skies...

The DEC was pretty straightforward. Came apart OK, needing a couple of taps top pop out bearings, cleaned up nice, regreased, reassembled. I'm not sure where Astro-Babe gets 2 hours from, it took me 4 hours to dissassemble, clean, regrease and reassemble. I did a rough retune on the worm gears before starting on the RA.

First mistake - I should have taken a break and waited till the next day. Black is not a good clolour for a mount when trying to do delicate things in poor light at 3 am with one's eyes hanging out.

The RA was a swine to get opened - the housing would not come off the brass gear. I had to use a combinatioin of thick bladed screwdriver and rubber mallet to force it out of it's sleeve. Interestingly, this is the one that whines with the SPX. I cleaned and regreased and reassembled - and the RA was stiffer than ever.

The next evening, having spoken to Astro Babe, I took the RA apart again. I ensured all the bearings were properly housed, and put it back (also requiring a rubber mallet to get the housing back) ensuring that nothing was being compressed. When all was back, the motion was stiff compared with the DEC, but better than before, and better than it had been before I started.

On to tuning. The next major problem. The hex-cups in the grub screws were worn, and I managed to get the worm gears roughly aligned, when the front one just gave up. Using a larger 'star' shaped tip a bit larger than the allen key I was using, tapped into the end of the grub screw gave me enough leverage to extract it. The rear one was little better - on the way to get the worm gears to align in a way that eliminated any wobble, the grub screw had to be tightened so far, that it dropped through the other side. Inspection of the grub screws showed that the front one was about twice as long as the rear. A trip to a hardware store failed to turn up any replacements, but I did find some screw/bolts that would fit. I found a supplier of grub screws online, and these are on order.

The screws/bolts allowed me to tune the worm gears (which I will swap for grub screws when they arrive). The mount has a very different feel to how it was before. Everything is tight, and the drive motion seems smooth. A clear night and I will check out the SPX.

I am very grateful to Astro Babe, as I messaged her and she was able to give some suggestions, and just having access to somebody who has done this themselves when you do run into any problems is very helpful. We agree that it sounds like somebody has had a go at this before.

I guess it is good to know how the mount works, inside and out, and short of sending it away I don't see how this could have been avoided. But, it is a nasty, dirty, fiddly job. The end-bearings and gears were all fairly well covered with tarry-black grease. There were no noticable bits of swarf. However, the tuning process makes sense now, having disassembled down to the worm gears.

If I knew what this entailed, I'd never have started - but knowing what it entails, I'd have no worries about doing it again. I will follow this up with a report when I have replaced the grub screws, had time for the worm gears to bed in. It 'feels' more solid already, having eliminated that irritating wobble on the RA that I could never quite figure out how to fox before.

M.

[themos]

I am not quite sure what some of those terms mean but it sounds like you're on top of things. Well done!

[MishMich]

Astro Babe suggests 2 hours for a competent person with the correct tools for each axis (I'm not that competent...). I found the DEC took me 4 hours, the RA took 3 hours the first time I did it (it is very similar to the DEC assembly), and 2 hours the second time. I had all the tools, although the rubber mallet wasn't where I expected (it seems to have become part of the camping equipment during the summer), apart from the locking wrench. Fortunately I have a very old cast-iron plumbers wrench which did the job.

I found I had to improvise two tools to get at some bits. There is a nut that screws into the thread of the housing that holds the worm gears in place, and it needs a special tool to unscrew. I found that a cheap alloy eating fork I had, when the 2nd & 4th spike was bent back and broken off fitted the task almost perfectly, and was much easier to loosen, remove and replace the nut with. The other thing I found useful for removing the plate that the polar scope screws into was an allen key tool I got from Travis Perkins a couple of years ago; it looks like a penknife, with a row of 4 allen keys either side. By pointing two of the medium sized allen keys forwards, holding the body with with the hand rolled up like a fist, the keys pointing between my little & third finger and the thumb & knuckle of my index finger, this worked a treat. I have since found a key I have for popping car stereos out of their housing - I've not tried it, but I suspect that unless the plate is over-tightened, this would work fine as well.

I used the allen keys that are supplied with Skywatcher equipment where possible, nevertheless, because Synta appears use imperial fittings on screws etc. It looks like the grub screws are 1/8" diameter. I am replacing these with M4, which is the closest equivalent as far as I can tell.

I would estimate the time re-tuning/calibrating the two axes takes at least as long as the disassembly/reassembly of one axis should take, and will need revisiting as things bed in and the mount is tested fully loaded. I guess this took up to 12 hours, including tuning, but if you know what you are doing, it could probably be done in half that time.

M.

[Astro_Baby]

Hi Mish,

I should probably put a provison on that guide that my two hours is based on me being like a beaver with a big caffeine hit when I start work

I have done three strip downs on these mounts now and for me its pretty familar stuff. The guide was actually based on two complete strip downs and rebuilds. One to trailblaze, make notes and photograph and once again because I wasnt happy with a few things.

Tuning them, and I have always said this, is a monster task - it took me probably 12 hours to tune the mount to perfection.

Getting an HEQ% to run sweet relies on three things really;

(1) Good greasing and assembly of the two axis which means not overtightening stuff (as an aside my mistake on the first rebuild was to tigten everything down - a hangover from rebuilding car and bike engines) astro mounts need a much lighter, looser touch.

(2) Worm engagement - the alignment of the worm gears to the worms.

(3) Worm end float adjustment.

Items 2 and 3 are linked to each other. Tighten down the worm end float and the mount will be ever so solid - unfortunately the motors will also bind super bad and you'll be putting a lot of strain on things.

Its all about getting a balnce between tightness so theres no 'slop' and enough free running so the motors arent strained.

To regulat my HEQ5 to get that took a fair few hours over successive nights. Its a bit like rating a watch. You have to tighten this down a bit, see how it runs - whoops too tight, loosen it off a bit. Its all very slow and at times I wondered if I was going to be driven insane the first time I did it.

The holy grail is when the mount is quiet, smooth but firm etc and you can then pat yourself on the back and have a certain smugness

I'm sure if you did it again you'd find it a lot easier - its a bit like collimation in some ways.

Really glad though its gotten working again and I am sure with a bit of tuning you will be amazed how good the mount can be.

Mel

[simon84]

The holy grail is when the mount is quiet, smooth but firm etc and you can then pat yourself on the back and have a certain smugness

Just a quick question, when you say quiet do you mean just the softish whine of the motors as it slews?

[Astro_Baby]

Yes - but also the grating noise they can make when not set up well. After upgrading my standard HEQ5 to GoTo it suffered two problems. One was motor noise the second was motor bind when the motors jam.

The relatively soft noise of an HEQ5 can be softened more by fine tuning BUT I wouldnt have taken the mount to bits merely to reduce noise. It was fairly quiet to start with.

The tuning for me was essential to get the GoTo upgrade kit to work reliably but it was useful in other ways, the mount performs better, it has less play in it, its quiter and the axis move much smoother than before.

In fairness though I am a terrible tinkerer and suffer a mild form of OCD so nothing is ever really perfect for me

[MishMich]

This was my problem. The HEQ5 is not set up for Synscan, so when I upgraded it, all sorts of problems emerged. Part of that may have been down to the power pack - the rattling noise the motors make when the power drops is the same (I discovered) as when the worm gears are too tight. When I pushed the exposures up to 3 minutes, the slight trailing on stars was not going in the same direction, but either not there, or where they were, they could be in directions of 90 degrees from each other (and one or two were actually 'L' shaped. I wish I had done this as soon as I'd done the upgrade. I guess it is not as noticeble on the HEQ5 normally, because it slews at a snail's pace, as all it is really capable of is aligning a star in the eyepiece and keeping track of it. When you set the slew rate to 9, with a large tube, the original tuning is not good enough, and slews started and finished (and sometimes ground to a halt) with a horrible noise. I had hoped to avoid stripping it, but I think it was the only way I could get to grips with how to tune it (how do you tune a set of gears unless you can visualise what it is you are trying to do with them?). The sweet spot between where the axes wobble and where the motor strains seems quite small, and difficult to arrive at. My RA (at least) had always wobbled a bit, but no matter what I tried adjusting couldn't be fixed. After stripping and tuning, it doesn't. I might have been able to fix it without stripping, if I'd understood what to do - but I didn't, and now I do.

M.

[Astro_Baby]

Thats very true Mish - even when you have taken the mount to bits the worm gear tuning is a tough one to get your head around. I spent ages turning the wrong adjustment screw seriously.

You need to stay calm - work it out, try again. TRy to stop banging your head on the mount when things arent going well and (for me anyway) factor in lots of cups of tea and ciggy breaks with the occasional valium

[MishMich]

Yes, the grub screws do seem a bit counter-intuitive, we are used to screws pulling, rather than pushing.

M.