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TAL-1M motor gearbox woes


Penguin

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I have a problem with the gearbox on my TAL-1 that I hope someone can advise on. I was going to post in the TAL users group but can't figure out how to!

A couple of months ago, it stopped turning the scope. I could hear the motor whirring but the mount did not move. I have now taken the motor assembly apart to find the cause. There is a gearbox with about 10 little gears attached to the motor itself. They all appear to move fine but I found that when a little load is put on, the last gear inside the box will slip on its spindle. The other end of this spindle, outside the gearbox has one more big cog that turns the worm gear and thereby turns the mount.

So it seems to me that what is happening is that the scope etc is placing too much load on that spindle and hence the last cog in the gearbox is slipping.

The big cog outside the gearbox has 3 spring-loaded screws on it which can be accessed via a small sliding hatch in the motor casing. As far as I can see though, these screws don't appear to do anything!

Can anybody advise? I have thought of trying to fix the cog on its spindle with a dab of superglue but I feel this could end in disaster! Also, I have a feeling that the cog is supposed to be able to slip and may be part of some clever clutch arrangement since I can't any way of disengaging the motor when I need to use the manual adjustment on the motorised axis (I can never remember which one is RA and which is Dec!).

Any advice would be hugely appreciated.

Edited by Penguin
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Hi Penguin !

Sorry to hear about your troubles.

The Tal User Group has been unavailable due to software issues.

I had an issue with the final gear in the motor reduction gearbox, a few years back. My final cog tooth was mashed. I ended up having to get a replacement from Tal, in Novosibirsk.

andyh-albums-andy-s-gear-picture3853-tal-vega-motor-corrector-mashed-motor-gearbox.jpg

If your cogs teeth are in good condition, but it's loose on the shaft, then it may be able to be fixed by getting it brazed to the shaft? It's not something I've got experience in, so I don't know if that'll work. There may be a type of epoxy glue that could be used for fixing metals together? But all of that is moot, if the cogs teeth are worn. This is the weak point of the Tal mounts.

The big cog with 3 screws, you're talking about, is the motor clutch. Details of setting it up, in here....

http://stargazerslounge.com/discussions-mounts/156715-adjusting-tuning-up-your-tal-mount.html

Andy.

Edited by AndyH
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Wow! That guide looks brilliant. I think there's a fair chance I have been using it all wrong. I will go through that guide before I try anything drastic. I think the teeth are all fine on the cog.

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I have now a similar problem. I need a new gearbox for my Tal2 Mount (mashed teeth). I have contacted Yuri but not had a reply in 10 days. Is he still dealing with Tal spares or has his email changed for any reason. I last contacted him 8 months, with no problem.

cheers

Steve ago

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The three 'sprung-screws' mentioned by the OP are there to press on a clutch.

The idea is to have them as loose as you dare, so the mount will slip on the clutch and not the gears, that way if you bump your mount or it hits the pillar you won't damage the gearbox.

Of couse if this clutch is loose, then it will show up all your mount imbalance, which is good thing, as you shouldn't run with the mount badly out of balance

Derek

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I have now a similar problem. I need a new gearbox for my Tal2 Mount (mashed teeth). I have contacted Yuri but not had a reply in 10 days. Is he still dealing with Tal spares or has his email changed for any reason. I last contacted him 8 months, with no problem.

cheers

Steve ago

As far as I'm aware, yes.

I'd maybe try sending the email again?

Yuri Elovenko, uran@npz.spektr.siberia.net

As I say to everyone and you probably know, try adding a pic of the item you're after, to the mail. Always helps, I reckon.

Cheers,

Andy.

ps: Out of interest, is it the final drive cog that's knackered?

_________________________________________

The three 'sprung-screws' mentioned by the OP are there to press on a clutch.

The idea is to have them as loose as you dare, so the mount will slip on the clutch and not the gears, that way if you bump your mount or it hits the pillar you won't damage the gearbox.

Of couse if this clutch is loose, then it will show up all your mount imbalance, which is good thing, as you shouldn't run with the mount badly out of balance

Derek

Bang on, Derek !
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Yes, I thought they must have something to do with some clutch mechanism but could not see how it might work. I think I have either got those way too loose and/or I am badly out of balance. Probably both!

I must admit that I have not been paying a huge amount of attention to precise balancing, I just put the OTA horizontal at the start of a session and make sure it doesn't tip. Then I have merrily swapped eyepieces, added a Barlow, put an SPC900 in there and even an SLR. I think I may have shuffled the tube back a little with the SLR on it but only guessed at how much!

I just hope I haven't already damaged the mechanism.

Edited by Penguin
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The motor clutch is perhaps the most important part of the mount to get right. If it's real tight and you use the RA knobs manually, with the motor on, it might/probably will cause damage to the reduction gearbox. All the other stuff, like balancing, large RA clutch tensioning, etc, that I list in that wee guide will not cause damage, but will show up as slippage and basically the scope won't work as well as it could and should.

It seems that in most cases of reduction gearbox failure, it's that final drive cog that's the one that takes the brunt of the punishment. The sychro motors seem to go on forever. I'd love to be able to source a supplier of metal gears, as I think they are repairable. I reckon I could do it if I had the gear to hand. I have a couple of gearboxes that only need that final gear. Very frustrating.

Andy

Edited by AndyH
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Hi Andy,

Yes it's the final cog that's knackered. I now have three......

It is the one weak link in such a cracking little clock drive.

The final two cogs should have been case hardened, to toughen them up somewhat.

I will send a further email to Yuri and live in hope...

cheers

Steve

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I have not noticed any stripped teeth when I looked at mine and, having separated gearbox from motor, the gears all turned nicely by hand. Do you know which way to turn the 3 screws to tighten and which way to loosen the clutch? I think I might dismantle it again this evening so I can fiddle with it while watching Stargazing Live.

I know it was working a couple of months ago. It makes the same noises as always and the manual knobs turn the same as before (they have always been slightly 'lumpy' and I think that is where the last gear is slipping)

--- Alistair.

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Clockwise tightens.

If the gears look fine, check each small gear, to make sure none of them have stripped itself internally, so to speak. Each gear and corresponding rod/shaft have machined grooves, which prevents them from turning freely on each other. I've got one that has stripped itself internally. If you hold the next gear, and turn that one, it just spins on it's shaft.

A couple of pics may help show both the damage that can happen to the final gear and the machined grooves(is it called a 'key' or keying?)

6708793233_a6dd4042f9_z.jpg

6708808183_701996b057_z.jpg

Let us know how you get on, Alistair.

Andy.

ps:That final gear is pretty simple. Would be a godsend if we Tal users could source a batch.

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Followed the instructions on that other post, balanced the scope as best I could and sorted out the clutches and it all seemed to be running smooth. So I set the hour wheel to 0 and left it for a good 40 minutes. When I came back the hour wheel was on 10 minutes and the final cog appeared to have stopped moving. :-(

When the smaller clutch was loosened off, turning the manual adjustment knobs was smooth where previously it was 'lumpy'. I believe that when it is 'lumpy', the clutch is too tight and I am actually turning that spindle inside the last cog and that the keyway may be knackered. However I don't know how to dismantle the top/bottom plate on the gearbox so I can get a proper top-down look at the gears. It doesn't look like the gearbox is screwed together, it looks more like a brass rivet type affair.

I see from another thread that a Russian supplier has been found for these motors and gearboxes. If anyone can cross the language barrier to arrange a 'bulk' order from these guys I would definitely be interested in a TAL-1 gearbox and maybe a motor too.

--- Alistair.

Edited by Penguin
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Hi, Alistair.

To get a look in the reduction gearbox, unscrew the 3 screws in the bottom of the mounts housing. Take care the motor doesn't fall out and rip off the wires from the small circuit board. Once you turn the motor/gearbox combo round to face you, you'll see three sets of screws & nuts, securing the gearbox to the motor. Once you've removed them, the gearbox comes off with a slight tug. Now you can have a good look at the condition of the small gears inside.

Perhaps before you do the above try the following, to definitively determine that the clutches aren't slipping, as sometimes slippage may not be noticable or is intermitant.

Fully tighten up the 3 sprung screws on the main large clutch plate. Now fully tighten the 3 sprung screws on the small motor clutch. There now cannot be any slippage from the 2 clutches. Now, set the RA setting circle to '0' and run the motor for either 10mins or 1 hour. After 10mins the RA axis should have moved by one segment(10mins) on the circle, a full 6(60mins) if timing for an hour. If it hasn't then there probably is a problem with the gearbox. To confirm, open it up and have a look at the gears. Especially the last one, with the motor clutch shaft on.

Cheers,

Andy.

Edited by AndyH
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No no, I've done all that and got the gearbox out. So I have the gearbox separated from the motor and can turn the outside cog by hand and watch the gears spinning. That's how I know that the last inside cog is slipping: I can see the spindle turning and the final cog sticking and I can also feel the slippage.

What I am not confident about doing is taking the gearbox apart, as you have done for your photos, to closely examine each cog. I can only see them edge-on from the side of the gearbox. I want to remove on of the plates that the cogs are sandwiched between but they seem to be riveted rather than screwed. Maybe yours might be a later version of the gearbox. I'll try to get a photo of it tonight.

Is anyone in contact with Uri? If there are several people after gearboxes, it might be worth one of us approaching him rather that several separate requests?

[edit]When slowly turning the outside cog, I can see the inside gears moving slightly along their shafts and after a couple of them have met face to face, the final one starts slipping. I am convinced it is not clutch slippage. It is at least one and possibly several gears inside the box.[/edit]

Edited by Penguin
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Apologies. I mis-read your post :D

To take the gearbox apart, you have to drill out one side of the three pins that hold it all together. Once done, the pins would need to be replaced. The end of the pins are probably squeezed and flattened open in a small press, thus securing the two sides of the gearbox and gears inside.

Andy.

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That's what I thought. I won't be doing that just now then! I think would want to replace the pins with screws if I did embark on such a task. For now, it's hunt-for-new-gearbox time for me.

--- Alistair.

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Some interesting links to a UK supplier of gears, that 'may' fit. I note they do repairs and modifications to stock sizes(at extra cost).

The gear that is close to the final Tal gear that we have been talking about is a Spur gear, Module 0.4, 32 teeth. The bore diameter seems to be 3mm instead of the (roughly)4mm on the supplied Tal gear.

Opinions??

HPC Gears Sitemap

http://www.hpcgears.com/newpdf/spurgears_0.4mod.pdf

HPC Gears, modifications page

HPC Gears Repairs page

Cheers,

Andy.

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This thread is the reason that the Tal group needs to be reestablished. Andy is doing a bang up job of holding up his end! My Tal 1M clock drive is running like a train with only simple maintenance. One thing that seems to keep things running well is to simply spin the scope around the RA axis a few time every once in a while. It appears to free up the drive clutch. I have cleaned the drive clutches and lubed wih light grease and the wiped them dry.

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Hi Andy,

Excellent link. I will strip down one of my old clock drives and measure the final cog, hopefully it will be similar. I will post the exact sizes for the existing cog and also send a drawing to HPC gears for them to quote.

cheers

Steve

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My Tal 1M clock drive is running like a train with only simple maintenance. One thing that seems to keep things running well is to simply spin the scope around the RA axis a few time every once in a while. It appears to free up the drive clutch. I have cleaned the drive clutches and lubed wih light grease and the wiped them dry.

Good info!

That's very interesting, as I've done something similar with the RA steel worm and gear. I had forgotton about it until your post.

After I've done a strip down, which can often be every summer, when it's too light to do astronomy up here, I put the mount back together. After seting the worm and gear as well as I can, I remove one of the RA hand wheels, put the M6 bolt back in, fit a driver in my hand drill and slowly turn the brass gear, at least one complete revolution. I feel it helps the worm and gear bed in. Perhaps it doesn't help really, but it's something I always do.

Andy.

Edited by AndyH
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Hi Andy,

Excellent link. I will strip down one of my old clock drives and measure the final cog, hopefully it will be similar. I will post the exact sizes for the existing cog and also send a drawing to HPC gears for them to quote.

cheers

Steve

Hi Steve.

My final drive gear measurements, apart from the I/D, look pretty much the same as the one I mentioned above. ie: 32 teeth, o/d 13.5mm , I/D 4mm, thickness 2.25mm. Note that it's an 'unhubbed' version.

If anyone out there has a broken gearbox in a cupboard, it would be interesting to confirm if we all have the same final gear and especially the same final gear shaft. Mine looks like this when taken apart.The size over the knurled part is 4.15mm. So would a gear with a 4mm I/D work? ie: when pressing the gear on, does the knurling bed into the gear?

6719262007_b5cf8aa2a5.jpg

I'd quite like to know whether the grooves inside the gear are machined in or whether they are formed when the gear is pressed onto the shaft?

Alistair makes an excellent point regarding using long screws and spacers to put the 2 sides of the gearbox back together. Would negate the need to get machined metal spacers made up and a lot of users could possibly perform this task.

This could be a significant step forward for users of Tal synchro mounts. It always irked me that I had to shelve a motor/gearbox combo, purely for ONE chewed gear. I've rarely heard of the actual synchro motor breaking down.

If when in contact with HPC, could you mention the fact that there could be a small market for a direct fitting replacement gear?

More questions than answers, so far, but turning into a great, great thread !!

Cheers,

Andy.

Edited by AndyH
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Apologies. I mis-read your post :D

To take the gearbox apart, you have to drill out one side of the three pins that hold it all together. Once done, the pins would need to be replaced. The end of the pins are probably squeezed and flattened open in a small press, thus securing the two sides of the gearbox and gears inside.

Andy.

I think I see what you mean now: the pins go right through the gearbox and stick out slightly on either side. I can then put it in a vice and gently squeeze so the pin ends splay out and lock the gearbox together. That seems do-able but where do we get the pins?

--- Alistair.

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They'd need to be machined up out of a 4mm diameter piece of steel or brass. Overall length 15mm, with about 2mm either end machined down to 3mm, to let the pass through the sideplates.

A friendly machinist could easily bang these out.

Would be interesting to see if your suggestion of using long screws, spacers and nuts would do. I think yes. I reckon they'd need to be countersunk screws, as you want the plate to be as flat as possible on the motor side of the gearbox.

Andy.

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There are lots of things I'd like that a 'friendly machinist' could bang out. Trouble is, I don't know one! I can easily get hold of a plummer or a carpenter or someone to fit new double-glazing but as far as I can tell, there's no such thing as a general machine shop any more. In days gone by you would pop into the local blacksmiths. The only place I can think of now would be the local secondary school but I doubt that the metalwork teacher would be too amenable to knocking these up or letting me loose in the machine room after hours.

Blimey that was a bit of a rant wasn't it?!

So basically, I'm asking how people go about finding such useful guys?

How much does a small lathe cost these days?

--- Alistair.

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