TheSkySearchers

Picked this up as an (almost) complete kit for $20 last week. I'm already reusing the mount, tripod, and other components in other projects but the OTA is missing the threaded plastic clamp that retains the eyepiece. :flame: I tried to swap with the eyepiece holder from a 70mm Meade but the threads on this scope are a tiny bit undersized and the Meade part just falls off.

The carbon fibre tube seems really sturdy and I'd hate to just toss it. Online search is not getting me exactly what I need which isn't surprising as that's not something you'd normally remove I don't think. There is no actual manufacturer info on the data plate. That and the fact that a Meade part doesn't fit makes me hesitant to make a blind purchase.

Any ideas on a substitute part or a simple fabrication? I wondering If I can make it out of PVC.

I think PVC would work fine. Canvass your neighborhood for someone with a lathe. It would be about a ten minute job to make up an adaptor from a PVC pipe coupling. There are more folks out there with home lathes than you might imagine. Check the local model railroad club and the local hotrod club. The Chesapeake & Allegheny Live Steamers certainly has members with lathes: http://www.calslivesteam.org

Possible. There is a hobby store in town that has a model railroad club. I'll check them out.

Check with Explore Scientific, they sell this telescope and may have some parts around. https://explorescientificusa.com/collec ... -telescope
You could also check Astro-Parts Mall, Telescope Warehouse or even Scopestuff.

Heh. I just saw one of those 70mm at Hobby Lobby yesterday. Didn't check the price.

pakarinen wrote: ↑Sun Jan 26, 2020 1:07 pm Heh. I just saw one of those 70mm at Hobby Lobby yesterday. Didn't check the price.

The one I rescued was the 2017 model which came with a terribly over bright LED finder scope. The newer ones seem to have reverted to more conventional/useful finders. Having already dropped the OTA once, I can attest to the sturdiness of the carbon fiber construction!

I found a bit of PVC scrap that seems about the right size for the eyepiece holder so that's option 1.
I also picked up a an old Meade 60mm OTA for a whopping $6 that I might be able to extract the entire focuser from to repair the NatGeo so that's option 2.

What I neglected to mention is that this is ongoing project #4 and I just had a brainstorm for project number #2 so I need to run out and get more parts for that one!

Thanks for the help everyone and stay tuned.

Update: Well the Meade focuser was a bit to small. The gear teeth and the focuser knob couldn't mesh when moved to the larger plastic focuser body. So much for option 2.

Back to the hardware aisle!

Edit: Oh and while I had it disassembled, I reversed the focuser tube so instead of the undersized threads, I now have a clean square plastic tube end to work with.

Too much fun!

Brain storm; instead of trying to manufacture a custom part, can't I get a cheap 1.25" extension tube and either glue or screw it in place to hold the eyepieces?

https://www.ebay.com/i/192591340777?chn ... 8sQAvD_BwE

No reason not to try it out

Well for eight bucks you can't go far wrong.

Ordered!
Expected delivery on or about Mar 9.
(to be continued ... )

And while I wait, on to the next project!

Perfect fit!
Final decision: Screw or Glue?

If I use a screw I'd want to drill and tap the aluminum extension tube but the draw tube itself is pretty thin plastic and I'm afraid it would crack if (when) I bump it in the dark.

If I glue it in, it's permanent. For the price that's no big deal. Plus that would remove any play in this particular joint. I'd just have to lightly sand the inner surface of the draw tube and the outer surface of the extension tube. I don't think thermal expansion would be a problem on a part this small.

Am I missing anything?

I vote for glue. Threads in thin plastic won't be reliable.

I figured to drill a full dia hole in the plastic and only thread the aluminum but that's still pretty soft and therefore risky.

Yeah. I'd predict that the al. is not one of the more machinable ones. Much of that extruded stuff is "sticky" when machined and soft. If the rack is removable, you could replace the tube with a bit of 6061 tube which would take threads nicely. Then put the rack on the 6061.

Of course, if you really want to jump off the deep end, you could go to Stock Drive Products and get a new rack and pinion (https://sdp-si.com). Then you'd have to find the tube off Ebay as the o.d. is more than likely metric. McMaster has lots of al. tube but I don't see any metric o.d.s. (mcmaster.com) Some time with Google will turn up metric tube suppliers.

Perhaps it's time to buy a lathe! :smile:

So ... glue!

Just remember to give the tube and adapter a good scuff before gluing.

Just had to let the glue cure overnight, clean off a tiny amount of excess at the seam and, it's done!
The squirrel population is starting to lodge invasion of privacy complaints but the weather forecast may be better tomorrow.

I'm declaring this project DONE. Thanks to everyone for the help and ideas.

https://media.giphy.com/media/vN3fMMSAmVwoo/giphy.gif