Show us your Tal

[John_D]

4 hours ago, Superewza said:

Alas, no storage box. I did notice a bit of bubbling under the paint, so I guess repainting could be in order. I do like teal...

I have a few ideas for what might work to hold the spider. Maybe just countersunk washers, on top of some rubber or felt to block the light. I'm not entirely sure what the purpose of the bit that sticks into the tube could be. Failing that, we do have access to a 3d printer. Kind of tempted to print a new focuser if the old one isn't going to work with new eyepieces anyway.

Yeah, the paint is bubbling on mine as well. Because the OTA is aluminium I didn't fancy the hassle of repainting so I decided that I could live with the patina.

If you've got access to a 3D printer then it's definitely worth a go to print the parts. I suspect that it's unlikely that places like Thingiverse has the right part but you never know.

[Superewza]

Huh, I would have guessed it would be steel, guess I'm too used to dealing with old cars where bubbling paint is always because of rust. Tested with a magnet and it does not in fact stick to the OTA, but it does stick to the pillar for the mount.

[John_D]

9 hours ago, Superewza said:

Huh, I would have guessed it would be steel, guess I'm too used to dealing with old cars where bubbling paint is always because of rust. Tested with a magnet and it does not in fact stick to the OTA, but it does stick to the pillar for the mount.

Yes, the paint on the pillar of mine is perfect. I guess that the painters at the TAL factory were pretty good when it came to steel. Aluminium less so 😁

[Superewza]

Well, I decided I'd just go through and figure out the bolt sizes of everything on the OTA, thought it might help if anyone else is missing bolts as I am. It's tempting to just replace any bolts which might actually get touched with hex heads or something too, always feel like I'm going to slip with a flathead screwdriver and take a big gouge out of the tube. Obviously these are measured as "stock", if you wish to move the mirror up the tube you will need longer screws there.

• Primary mirror cell to main tube
  • 3 of M4 x 6mm countersunk head screw (these could be longer, the hole is threaded all the way through and there's nothing for it to foul on the other side)
• Primary collimating screws
  • 3 of M4 x 20mm socket cap screw, with 3 roughly 9mm long springs (obviously lots of springs would work here, or you could get a longer spring and cut it down)
• Primary collimation locking screws
  • 3 of M4 x 12mm socket set/grub screw, cone point
• Secondary mirror spider to main tube
  • 4 of M4 x 4mm countersunk head screw with washer*
• Secondary mirror holder
  • 1 of M5 x 16mm socket cap screw, with a roughly 10mm long conical spring
• Secondary collimating screws
  • 3 of M5 x 20mm socket set/grub screw, cone point
• Spider to secondary mirror cell
  • 6 of M3 x 6mm slotted mushroom or wafer head screws (just as low profile as you can find, these have the potential to stick out into the tube and not be fully obscured by the secondary mirror)
• Focuser to main tube
  • 2 of M4 x 6mm button head cap screw or similar
• Finder scope to main tube
  • 2 of M4 x 4mm countersunk head screw
• Finder scope adjustment screws
  • 6 of M4 x 10mm thumb screws, (ideally) cone point

 

* These come with a strange washer which I haven't been able to find a direct off the shelf replacement for. Closest thing I've seen is a flanged sleeve bearing if it also had a countersunk washer on top, but none of the ones sold match the 12mm O.D. 9mm I.D. of the part that goes into the tube. It would be pretty trivial for someone with the right tools to machine, but you could also just use a flat M4 countersunk washer instead. The part that goes into the tube picks up on the threaded cylinders on the ends of the spider, so it might make it a bit harder to locate initially but once everything is held in tension I can't see it causing any problems (and may slightly cut down on light being blocked in the tube). I think you'd want the 16mm diameter ones, any smaller would risk just falling through the 12mm holes in the tube, any bigger would risk fouling on the focuser. The originals are just flat where they sit on the outside of the tube, but it might be a good idea to add a rubber washer underneath to protect the paint, and also block any light or water ingress through the holes. Increase the length of screws you use appropriately.

[DaveL59]

On 28/08/2024 at 16:07, Superewza said:

Howdy! I remembered visiting this forum when I was in my teens so I thought I'd check in now I actually have a scope of my own 😁 My partner actually has a Skywatcher 200p, but honestly we rarely get to use it with how much of a pain it is to drag it out and let it cool down. Been looking for something that could be a bit more grab and go for a while, and picked this up for £30. Obviously it's going to need a bit of work...

I had hoped with it being from 1999, it might be late enough to come with a normal 1.25" focuser. Unfortunately it still seems to be the older push fit one, which moves alright but I'm pretty sure the plossl is well and truly seized in there. Mixed blessings I suppose as it's the only eyepiece it came with, I can unscrew it from the main tube but I'm pretty sure that's part of the focuser itself.

A couple of other things are a bit different to other TALs I've seen. The mount screws into the post, instead of just sitting in a cup at the top, which is neither here nor there really. But the way the OTA attaches to the mount seems different, the rings are actually part of a single assembly that's fixed to the mount, instead of the rings being on the tube which then have a flip bolt to secure them to the mount. This seems like it would make it hard to put anything else on this mount if I ever wanted to. Also means you have to balance it each time you mount it, I guess you could mark the correct position on the tube somehow.

When I took the dust cover off, a solitary little spring fell out. I don't actually see any on the mirror assembly, so it might be a good idea to just move the mirror up the tube from the off. I don't see any obvious scratches or pitting on the mirror, but it does seem to have fingerprint smudges on it so we'll see how that turns out after a clean.

The whole thing is begging for a proper teardown, clean and regrease, so we'll see where we stand after that. After a quick inventory I am missing:

• Two screws to attach the focuser.
• One of the screws and silver cups for the spider (this could be a pain to track down)
• One of the plastic feet that fits into the cups on the end of the legs.

Is that a TAL2 or a 1?

The focuser does look like a 1.25-inch version rather than push-fit 32mm so there'll be a locking screw on the ring somewhere, perhaps sheared off. The one on my TAL-1 that I retrofitted below. That 25mm Plossl also doesn't look like the older 32mm one I have, different barrel knurling/shape.

I used a nylon screw to replace the original metal one.

Like yours, my TAL-1's mount screws into the pillar rather than fitting into a cup, has the fixed rings also. I find for the few steps out of the conservatory to the garden I can just pick the lot up in one and drop it where I need it to be 🙂

I did also buy a pair of OTA rings, for a SW130 IIRC and one of those fitted above the top ring will let you easily place the OTA at its balanced position and also rotate the tube when required.

If I remember correctly, the small screws for the focuser are M3, probably ally else you get galvanic corrosion issues (if steel ones are used) so probably harder to find. Might be wrong tho and you could always just tape the holes to take a bigger size if that's easier 😉 

Edited September 2 by DaveL59

[Superewza]

Huh, it seems you were right. I missed the thumb screw on a first glance because, uh, this is all that's left of it. It feels like plastic though so should be easy enough to free up or just drill out. I guess I can find out for myself how well it works with modern eyepieces then, the focuser definitely doesn't get very far in, it stops about 2cm before it would even begin to enter the scope.

Thanks for the tip about corrosion, I have some ptfe tape that's used to seal threads of plumbing fittings, which would probably do the trick. The threads on my tube might just be chewed up, it wasn't the smoothest going in but an M4 was the only one that would go in at all. Might have to get a tap and die set, then I could move the finder if I need to. My left eye is pretty lazy...

[DaveL59]

handy to have a suitable tap for sure, if you plan to repaint, since you can clean up the threads without damage. Did the same on my TAL-M when I overhauled that 🙂