Tal 2M mount problem

[dark star]

Hi, I have a problem with my Tal 2M mount, the metal connecting/ holding the Dec axis slow motion control to the dovetail has broken. This not only means that I can't use the slow motion control it means that the Dec axis swings freely until it is stopped by a knob.

Does anybody have any idea how to fix this without welding, machining etc. ?

I can probably stop it swinging around by wrapping string or wire around the Dec axis dovetail and the dovetail of the telescope.

Has any Tal 2M owner had this problem and if so how did you fix it? Any replies gratefully received.

David

David

[AndyH]

Do you mean the 'tab' that is part of the upper plate casting and fits between the slo-mo knob unit?

Andy.

[dark star]

Hi, yes, that is right. I have managed to make the mount usable again by wrapping string around so the Dec axis does not swing freely. It would be nice to be able to fix the slow motion control.

David

[AndyH]

A T piece of steel or alluminium can be screwed to the the top plate as a replacement for the broken cast piece.

The DEC axis will have to be removed to let you get access to the top plate.

Andy.

[dark star]

Thanks a lot. I will have a look at the weekend. How does the metal T connect to the slow motion control? There is a square nut around the slow motion control which has partly broken off, I think it must have been attached/ welded to the top plate.

David

[AndyH]

Can you upload any pics ?

It would make it easier to help & explain.

SGL user and Tal 2M owner, Stargazers Lounge - View Profile: jamespels , has his DEC arm off for repair. Hopefully he may see this thread and join in the discussion and offer some advice.

Normally I'd strip mine down to help, but I've taken ages to align the 3 scopes my 2M mount is carrying and would rather leave it as is for the mo.

Cheers,

Andy.

[dark star]

I will take some pictures at the weekend, I think I will need a fair amount of time to take everything apart. Just unwinding the string I used to stop the Dec axis flopping about will take a while!

David

[dark star]

Hi, I have taken some photos of the broken slow motion control on the Dec axis of the Tal 2M mount, and of the top plate that it was attached to showing where it broke off. Any advice on how to fix this gratefully received.

David

[TheThing]

Ah yes, common problem. Happened to me. I was lucky enough to get hold of an old mount and swap the parts over.

It's aluminium so wont wel easily. A motorbike repairer might be able to do it.

If not, you'll need to screw/bolt something thru. The slow mo control comes apart quite easily. it has a fairly strong spring in it though.

[AndyH]

Hi.

Here's what I'd do.

1/ Take out the broken 'tab'. Place it back onto the break where it came and take measurements

Also measure the width, length and thickness of the tab.

2/ Grind or file down the broken stub on the body of the mount.

3/ Source a small piece of 'T' shaped steel or alluminium, as close to the size of the tab as possible.

The following site shows sizes that are available(in alluminium)

Richard Austin Alloys Ltd - Aluminium and Stainless Steel

4/ If the clearance between the upper mount plate and the lower slo-mo plate is wide enough, then a T piece section can simply be screwed on(or rather, bolted on) to replace the broken tab. If there isn't enough clearance, then you'll need to create a slot(mutiple small holes close together, then file through them to form the slot) where the tab was and screw(or bolt) the T piece in from the the top, making sure it's long enough.

5/ You'll need to dissasemble the DEC shaft to be able to then fit the repaired top plate, with new tab, between the slo-mo wheel's threaded end and the sprung pusher.

One thing I should also mention. Looking at your pics, this is the MT-1C version rather than the 2M or MT-2C mount. This was the motorised mount offered with all Tal scopes other than the 2M(6"F8) Newt. A fine mount none the less.

Andy.

[dark star]

Thanks a lot. I will have a try at fixing it at the weekend.

I now have a mount that I have never heard of before!

The main thing is that it seams to handle my 10 kg 250mm reflector OK. I thought it was not as incredibly heavy as it is supposed to be!

It may be just as well, as this mount is probably lighter than the 2M mount, and I have to carry it a reasonable distance from my shed across the garden.

David

[AndyH]

The reason why I didn't suggest welding is because the mount is cast alluminium, which I don't think will weld well. I could be wrong on that. Whilst I've welded other types of material which are cast, I've never tried alluminium

Also, this tab is basically holding the weight of the scope, so if the weld isn't perfect and strong, it'll possibly/probably snap again.

Andy.

[dark star]

Does anyone have the MT-1C mount?

I would be curious to see some pictures just to be sure this is the mount I have. I have been looking at the manual for the Tal 2M mount for months and didn't notice any differences!

Is it just a scaled down version of the bigger mount? If so this would explain why I didn't spot anything different. However I am not very observant so this may also explain it!

David

[AndyH]

Some 2M/MT-2C sizes........

It has a 270mm long by 80mm wide top plate. The DEC shaft/axis is approx 60mm diameter before it tapers down as it comes to the setting circles, which are 4" in diameter. The mount pillar is approx 4 3/8" outside diameter.

From what I can remember the 2M/MT-2C was originally intended, way back, as a mount to hold a prototype Tal Maksutov. For unknown reasons, it seems it was only the 2M or 6"F8 newt that came with this mount.

The MT-1C was the ranges workhorse as it was used for all the other scopes.

The 2M isn't manufactured anymore(although it can be if you place a minimum order of 30 pieces!!) as the newer stepper mount, the MT-3S, is used to carry most of Tal's heavier scopes now. To confuse matters even further, there is also a beefier version of this, the MT-3S2D. I don't think many of these stepper mounts were imported into the UK.

Andy.

[dark star]

Hi, my top plate is 230mm long and 50mm wide, the setting circles are 3 inches in diameter, so I suppose it must be the MT-1C mount.

On the other hand the motor assembly on my mount looks exactly the same as your picture of the Tal 2M mount on the Yahoo Tal users group website!

David

[dark star]

One question, how do I bolt the T section to the top plate?

David

[AndyH]

I'd probably use M3 or M4 setscrews.

Ideally I'd drill and tap threads on the mount plate and corresponding unthreaded holes on the T piece. It would be more secure and less likely for the T piece to move when under a load.

Andy.

[AndyH]

The motor and gearing housing is the same on both mounts. In fact they both use the same motor/gearbox, motor clutch, worm and gear. The only difference I believe is in the RA shaft that holds the bearings and brass gear wheel & clutch. I'm not 100% sure as I've not seen pics of this mount stripped down.

Andy.

[steelfixer]

Dark Star

Andy is quite right it is a pain to weld unless you have the right gear to do it.

Fortunately I do have the gear as I own a steel fabrication business.

So if you get completely stuck you can post it down to me and I will weld it up for you.

All it will cost you is the postage.

Graham

[dark star]

Thanks a lot for the very kind offer. I will keep trying myself for a good while, as there are lots of useful skills I could learn that will probably come in useful in the future.

For example how to drill holes in metal. I haven't done this since metal work at school, which is a long time ago, and I was very bad at it!

Is it possible to use bolts? As to begin with I think drilling the holes will be challenge enough without tapping threads. I need to check that the drill I have can do this, and also to buy a vice.

Just in case I decide to try, can a hand held drill be used for tapping threads?

David

[dark star]

I have watched a couple of D.I.Y. videos and drilling and tapping doesn't look very difficult so I will probably give it a go. I just need to get the necessary equipment.

David

[steelfixer]

no problem David If it all goes pear shaped make sure you keep all the bits and I will probably be able to put it together again for you.

graham

[datman]

Hi

I was going to offer to make one until I saw Grahams offer. Unless you take time to learn (as in reading about) how to drill and tap I fear you are destined for a screw up. I would seriously consider Graham's very generous offer.

[dark star]

Hi

you are probably right, but I am afraid I have already bought a tap and die set from Maplin!

I realise that, for me, this will be a real challenge, so I intend to do a lot of reading.

I am hoping that the worst I can do is drill two small holes in the top plate and not succeed in tapping the threads, and that the mount will still be fixable!

I will probably spend a week or two reading and measuring everything, plus I still need to buy a vice.

David

[datman]

Hi

Ok what is most important is that you mark very carefully where the holes will go and punch the holes (not with your fist that will hurt).

If you don't have a punch you could get away with a good nail since you are drilling aluminium. If you put the punch on the hole and give it a tap with a hammer. This will stop the tapping drill going for a walk when you start drilling.