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  #41  
Old 10-04-2018, 04:38 PM
Stefan Buda
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Hi Rod,

The 10" was made in the late 90's and I don't have much documentation on it, while the 16" is reasonably well documented, I doubt I could find the time for a dedicated thread for it. However I'm happy to dig up photos on request dealing with various details. When I was making it, I thought that it was going to be the first Peltier cooled planetary telescope, but I found out later that Anthony Wesley was working on his own 14" version about the same time.

To get back to the present: I made a first iteration mock-up of the spider/front ring.
I'm going on uncharted territory here, like I did with the Peltier cooled primary, so I have to proceed carefully. The idea is to make this important part of the OTA through 3D printing.
This mock-up study was printed with ABS filament, but the real thing will be printed with carbon fibre reinforced polyester filament, which has a modulus of elasticity about 3 times higher than ABS. Even that may not be enough so I intend to embed some uniaxial carbon fibre as well during the bonding of the parts. Also very thin ribbon cables will be enclosed in the vanes for power and signals. The finished vanes will be about 2mm thick.
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  #42  
Old 10-04-2018, 05:18 PM
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Lognic04 (Logan)
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Wow, very cool that you are 3D printing the spider! Not too long until people start 3d printing whole telescope tubes!
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  #43  
Old 11-04-2018, 12:52 PM
Stefan Buda
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Originally Posted by Lognic04 View Post
Wow, very cool that you are 3D printing the spider! Not too long until people start 3d printing whole telescope tubes!
It's been done, just google "3D printed telescope", and you will find a few examples. Except those are not very useful telescopes.
I intend to use 3D printing only in ways that will not compromise performance.

I have fished assembling the mandrel, this morning, and I'm very envious of Elon Musk because he made a bigger one.
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  #44  
Old 11-04-2018, 02:03 PM
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I have fished assembling the mandrel, this morning, and I'm very envious of Elon Musk because he made a bigger one.
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  #45  
Old 12-04-2018, 02:37 PM
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Wow, very cool that you are 3D printing the spider! Not too long until people start 3d printing whole telescope tubes!
The French have 3D printed entire houses so entirely possible
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  #46  
Old 14-04-2018, 11:47 AM
Stefan Buda
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Let's get on with the phlog.
I rigged up a stand for the laminating procedure and the inner skin went on very nicely. The resin gave me about 25 minutes to complete the job, and that turned out to be just enough.
I want to sand the surface a bit before I laminate the Coremat, but I have to do that outside and the weather has turned bad.
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  #47  
Old 14-04-2018, 04:53 PM
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Thanks for the info


From the picture looks like you wrapped the first layer around mandrel and then applied the resin after that. When you completed wrapping the carbon fibre did you use a vacuum bag for it to set?
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  #48  
Old 14-04-2018, 05:44 PM
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Thanks for the info


From the picture looks like you wrapped the first layer around mandrel and then applied the resin after that. When you completed wrapping the carbon fibre did you use a vacuum bag for it to set?
It's not very clear from the picture, but first I applied a generous coating of resin onto the mandrel and then I wrapped on the two layers, feeding the cloth under a slight tension. Only after that I brushed on the remaining resin.
The mandrel is very smooth and cylindrical and the cloth conformed very well, without trying to produce bubbles. I wanted to avoid vacuum bagging because the 3D printed skin of the mandrel would distort under the pressure. However, after the resin has gelled, I did wrap the ends of the tube and the seam with 50mm wide masking tape, just to make sure that the carbon conformed well to the mandrel. After about 4hrs I removed the masking tape.

Last edited by Stefan Buda; 15-04-2018 at 03:06 PM.
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  #49  
Old 15-04-2018, 03:04 PM
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The weather cleared yesterday afternoon and I was able to do the sanding down of the tube.
After I brought it back inside, I laminated the 3mm Coremat, using about one third of the amount of resin that it should be able to absorb. I painted the resin onto the carbon fibre only, as I wanted the outside of the coremat to remain dry for wrapping. I first wrapped the coremat with baking paper, as a barrier layer, and then with masking tape. After about 5 hours I removed all the wrapping. Today I will saturate the coremat with resin and wait for the next weather clearing.

BTW does anyone have any good internet links pointing to carbon telescope tube making? People seem to be a bit shy about revealing their techniques, or at least I didn't have much luck finding good information.
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  #50  
Old 15-04-2018, 03:36 PM
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Thanks Stefan,
yes that's cleared it up. I also thought resin had to go in-between the layers, but that's cool I'm learning all the time.
What brand of resin are you using?

I agree on the little information on the net about making tubes of carbon fibre I searched about three months ago and it was hard to come by.

Cheers
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  #51  
Old 15-04-2018, 05:50 PM
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Quote:
Originally Posted by Stefan Buda View Post
BTW does anyone have any good internet links pointing to carbon telescope tube making? People seem to be a bit shy about revealing their techniques, or at least I didn't have much luck finding good information.

You could PM David Fitz-Henr. He's a member here and built his own newtonian.
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  #52  
Old 16-04-2018, 08:00 PM
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Thanks Stefan,
yes that's cleared it up. I also thought resin had to go in-between the layers, but that's cool I'm learning all the time.
What brand of resin are you using?
Cheers
The carbon cloth is very good in soaking up the resin, but you would not want to skip more than one layer without applying it.
I use R180 resin with standard hardener. Cost is about $50 per 1200g from Allnex.

Quote:
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You could PM David Fitz-Henr. He's a member here and built his own newtonian.
Thanks Mark, I had a look, but David bought the tube for his Newtonian.
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  #53  
Old 20-04-2018, 07:47 PM
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Some more pics:
The first one shows the tube after laminating the outer skin with extra resin.
The second one, after it has been sanded back and recoated with more resin.
The third shows it after a second sanding, while I started cutting it to length on the lathe.
All that's left to do is, the 2k polyurethane, UV resistant clear coating.
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  #54  
Old 20-04-2018, 09:21 PM
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Originally Posted by Stefan Buda View Post
Some more pics:
The first one shows the tube after laminating the outer skin with extra resin.
The second one, after it has been sanded back and recoated with more resin.
The third shows it after a second sanding, while I started cutting it to length on the lathe.
All that's left to do is, the 2k polyurethane, UV resistant clear coating.
How did you machine CF? I remember going through a lot of saw blades shortening my C11 CF tube.
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  #55  
Old 21-04-2018, 09:26 AM
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I used a high speed steel tool and by the time I cut trough the inner carbon layer, it was quite blunt. After re-sharpening it, I took another very small cut to produce a nice clean and square end. So I had to sharpen the tool twice for each end.
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  #56  
Old 23-04-2018, 07:24 PM
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Tube finished.
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  #57  
Old 23-04-2018, 08:55 PM
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slick ass... whats the wall thickness?
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  #58  
Old 24-04-2018, 07:28 AM
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Tube finished.
Beautiful work Stefan, it seems you have a lot of spare time so how about making some UTA rings for me, say 503mm ID, 600mm OD and 12mm thick ....
3k twill should do.....
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  #59  
Old 24-04-2018, 08:07 AM
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Originally Posted by Joshua Bunn View Post
slick ass... whats the wall thickness?
4.7mm

Quote:
Originally Posted by Kunama View Post
Beautiful work Stefan, it seems you have a lot of spare time so how about making some UTA rings for me, say 503mm ID, 600mm OD and 12mm thick ....
3k twill should do.....
Thanks Matt,
Yes I do have a lot of spare time at the moment. The laser equipment manufacturing industry has just about disappeared in Australia, so work has been very sporadic for me in the last few years. I should probably switch to astro gear full time.
However with your UTA rings I can't see a cost effective way of making them, partly because of the big wastage of carbon cloth that needs to be cut and effectively destroyed in the process. If you can think of a good way of doing it, I could have a go at it.
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  #60  
Old 01-05-2018, 12:33 PM
Stefan Buda
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I ordered some Borofloat blanks from Germany and looks like I won't be getting them until July. I wanted to make a start on the primary before then, so I dug up an old school Pyrex blank from my collection and spent several days machining it down to 25mm thickness. Actually I overshot the mark by half a millimetre.
I just have to generate the front radius and I can start pushing glass. I already have a thick Pyrex tool that I made for re-grinding an ODK10 primary.
The radius difference is very small and I will fine tune it with a metal ring tool.
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