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Unsure how to join these telescope mounting pieces

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choochoo_baloo26/05/2020 14:19:04
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251 forum posts
54 photos

By now most of you will recognise my username, and each time I qualify with “I’m a novice” or similar, but if not...baby steps please!

I need join this aluminium ring to this stainless steel plate to house my telescope mount.

losmandy_ring1.jpg

losmandy_ring2.jpg

My initial plan is:

  1. Machine shallow circular pocket on stainless plate, by holding flat on a 9” faceplate (I have an ML7). It's only 4mm thick though.
  2. Seat the ali ring
  3. Flood with Araldite.

However the Araldite would bother me. That ring is going to seat a few £1000s worth of delicate equipment, and I think as telescopes move, torques are going to pull at the base, and possibly crack the epoxy.

But I'm struggling with alternatives because of the unusual shape.

(Can stainless and aluminium be stick welded together?)

Hoping the helpful folk on ModEng forum can help me out!

Mick B126/05/2020 14:26:40
1578 forum posts
84 photos

If the plate disc at the base is 4mm thick, it looks to me as if you've room for quite a few M5 or even M6 socket-head countersunk screws into the tube, square to the disc. A turned or bored register might help, but possibly not essential.

Edited By Mick B1 on 26/05/2020 14:27:50

old mart26/05/2020 14:26:55
1776 forum posts
138 photos

What about using small screws through the SS and threaded into the aluminium? The wall thickness of the aluminium looks like 5-6 mm, so 3mm screws would probably work, you could fit dozens in there, that would safeguard the telescope.

Michael Gilligan26/05/2020 15:45:18
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15735 forum posts
687 photos

Araldite [epoxy resin in general] is very difficult to use reliably on Aluminium alloys.

I would certainly be looking for an alternative to step 3

MichaelG.

old mart26/05/2020 16:50:14
1776 forum posts
138 photos

Bare aluminium should be shotblasted to give a bond for araldite, chromic anodised is much better for adhesion.

Neil Wyatt26/05/2020 17:13:00
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17897 forum posts
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Rather than recess the plate, make full use of its depth.

Temporarily locate with superglue. Drill and fit plain pins to locate accurately.

Drill and tap for M5 csk screws which have a head depth of 3.1mm, or M4 ones if you are less confident.

I would definitely prefer M5 to M4 and wouldn't rely on M3 to take a heavy shock load in aluminium.

Ideally, get an aluminium base plate and get someone to weld them together.

Neil

old mart26/05/2020 17:39:49
1776 forum posts
138 photos

Niel, if there is room for 24 three millimetre screws, that would certainly take care of any shock loads that might happen.

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