Adventures with an old SW 300p

[markse68]

2 hours ago, CraigT82 said:

Ive seen a few people reinforcing the upper tubes with sheet aluminium riveted/screwed on the inside or outside of the OTA, to make it all stiffer up at that end.

I wonder if you could 3D print a section of tube, with an OD just less than the ID of your OTA and a wall thickness of a couple of mill, to slide down inside the OTA beneath the focuser and reinforce that area? 

Could even glue it in place instead of screws or rivets so it would be an invisible reinforcement? 

oh i don’t think it’s the OTA tube Craig- that’s a 4-5mm thick “hard paper” epoxy laminate from Neumann-  it’s very rigid and strong i think. No i think it’s the Feathertouch- it supports the focuser tube in bearings on one side of the tube only and whilst beautifully crafted, i think it’s prone to flex due to the leverage of the substantial offset weight of the camera. 

Mark

[Captain Scarlet]

Are you referring to the OTA tube material on the “blue-tube” Skywatcher Mark? It’s 1 mm steel, and not very rigid at all. Attached a pic of a hole I drilled out of mine to move the focuser a few cm up:

[markse68]

sorry Magnus for the mixup- no it was just an aside really that i’m getting noticeable flex in my focuser

Mark

[neil phillips]

Very cool Craig. You got me wondering about my mirror clips.  I had thought about changing them before. Nasty cheap wide metal strips, that could be a third of the width and still hold the primary just fine. Like your solution centering the focuser. Did mine much more slapdash. Using a colli and cheshire looking for concentricity around the flat. Yours is more accurate by far. You have this nailed by the looks of things, nice one. Question do you plan on using the fan while imaging ? My fan is a small low vibration maglev. I have it blowing air in. Tried imaging with it on. But works better switched off. 

Any way love the thread this is what its all about.

Edited June 26, 2021 by neil phillips

[CraigT82]

9 hours ago, markse68 said:

oh i don’t think it’s the OTA tube Craig- that’s a 4-5mm thick “hard paper” epoxy laminate from Neumann-  it’s very rigid and strong i think. No i think it’s the Feathertouch- it supports the focuser tube in bearings on one side of the tube only and whilst beautifully crafted, i think it’s prone to flex due to the leverage of the substantial offset weight of the camera. 

Mark

Shame about the Feathertouch, would have thought it would be a bit sturdier given their reputation, but that's interesting to hear about the hard paper tubes. Just been looking at the Gerd Neumann site and they are fairly cheap so may be an option to upgrade this tube (or for my as yet unborn self build 12" in the future).  With a density of 1.15g/cm3 and a wall thickness of 5mm it would be over 3kg lighter and hopefully somewhat stiffer than the OE steel tube. Very interesting! 

[CraigT82]

4 hours ago, neil phillips said:

Very cool Craig. You got me wondering about my mirror clips.  I had thought about changing them before. Nasty cheap wide metal strips, that could be a third of the width and still hold the primary just fine. Like your solution centering the focuser. Did mine much more slapdash. Using a colli and cheshire looking for concentricity around the flat. Yours is more accurate by far. You have this nailed by the looks of things, nice one. Question do you plan on using the fan while imaging ? My fan is a small low vibration maglev. I have it blowing air in. Tried imaging with it on. But works better switched off. 

Any way love the thread this is what its all about.

Thanks Neil. At the minute this scope is nothing more than a garage ornament! It hasn't had first light yet because with Jupiter and Saturn appearing in the early hours I just can't get out at that time unless it's clear on a Tuesday night when my boy is at his gran's. Even if it is clear I'm much more inclined to catch up on sleep rather than go out imaging (he doesn't sleep well and likes to start his days at 4am so I take the opportunity to catch up on sleep wherever I find it). Im hoping to be much more productive later in the year when they are in the sky in the evenings. 

Regarding the fan, I think it should be fine to leave running during capture as I didn't have any issues with it when it was fitted to the Fullerscope. It does have a speed control so I turn it right down, being a large fan even running at low speed it pulls a lot of air. 

[neil phillips]

1 hour ago, CraigT82 said:

Thanks Neil. At the minute this scope is nothing more than a garage ornament! It hasn't had first light yet because with Jupiter and Saturn appearing in the early hours I just can't get out at that time unless it's clear on a Tuesday night when my boy is at his gran's. Even if it is clear I'm much more inclined to catch up on sleep rather than go out imaging (he doesn't sleep well and likes to start his days at 4am so I take the opportunity to catch up on sleep wherever I find it). Im hoping to be much more productive later in the year when they are in the sky in the evenings. 

Regarding the fan, I think it should be fine to leave running during capture as I didn't have any issues with it when it was fitted to the Fullerscope. It does have a speed control so I turn it right down, being a large fan even running at low speed it pulls a lot of air. 

Sounds good. Do you think it may be worth reversing my fan trying to run it while imaging ?  sounds like you had good results doing this then ? 

See your dilemma about imaging planets at the moment. Moon not well placed either

 

[Captain Scarlet]

10 hours ago, markse68 said:

sorry Magnus for the mixup- no it was just an aside really that i’m getting noticeable flex in my focuser

Mark

Ah now I understand, you were talking about your own tube, not Craig’s, my apologies!

M

[CraigT82]

Managed to get first light with the 300p on Jupiter (16/07/21). Very pleasing result with the planet at about 30 degrees elevation. Was quite a lot of near ground seeing issues after the hot day too, so should be able to do better with better conditions.

 

Plans are afoot for the following:

1) fabricate new secondary holder from 50mm diameter delrin rod and glue secondary using three blobs of RTV technique (rather than square of thick double sided tape currently employed)

2) Build a Foucault knife edge tester and have a look at the primary. More out of curiosity than anything else. 

3) Fabricate a new primary mirror cell from 8mm plate and angle 6082 aluminium with 6 point floating rear support and 6 point edge support. Have purchased a drill press, bench grinder and other metalworking bits and bobs for this. 

Plenty to keep me busy for the foreseeable. 

 

[Swoop1]

Nice image Craig. Quite satisfying I should imagine.

[CraigT82]

Have made a new secondary holder from 50mm diameter Acetal rod. Acetal has a lower coefficient of thermal expansion than the aluminum of the original. The 50mm size is also much larger than the original, allowing me to use glue the secondary on using the 'three blobs of RTV' technique, as opposed to the OE method of a square of double sided sticky foam tape.

[CraigT82]

Well…. Have been a bit out of touch with the hobby recently so decided the best way to remedy that was to spend some money on Astro kit 😈. To that end I’ve just placed an order for a John Nichol mirror set to replace the scratched old skywatcher originals. Going to be a bit of a triggers broom this scope.