Hi guys, I have just started a project to build my own telescope. I wanted to design a scope that fits me a little better than my current one.
I decided that for the meantime I wont be changing my mount or my camera so the telescope was designed around these items. The main thing that I wanted to get right with this was the tube. It has to be rigid enough to hold collimation. I was not entirely happy with my current rolled steel tube so I decided that I would make my own. After reading about people making carbon fiber tubes using a mandrel I decided this would be the way to go. With this in mind i bought a packaging tube with a 170mm outer diameter to use as my mandrel which tonight I was coating with release wax. I have also received my carbon cloth and epoxy. The epoxy i bought locally, but the cloth was from soller composites in the states. I have sent a few emails to them and they recomended a layer of 3k 2x2 twill followed by 2 layers of carbon sleeving that they supply and then a final layer of the twill. I should have extra carbon cloth that I might use to reinforce the focuser area. The tube will extend 20cm past the focuser to stop stray light (a problem i have with narrowband imaging from the suburbs). I will completely cover the inside of the tube with flocking from scope stuff to help this also.
As far as the rest of the scope is concerned I am going to do is buy a VX6 which is a 6 inch f5 newt from Orion Optics with a 63mm secondary and ultra optics and transplant the parts from this into my custom tube. The values in NEWT give me a 100% illumination diameter of 25mm, ample to cover my kaf8300.
I will take some photos and upload them of the process as I progress through it. But I am looking forward to the result.
Hi Peter, I find it interesting to read that you purchased from Soller.
I'm in the planning stages of an 8" or 10" newt-astrograph and read that Soller can't send packages longer than 36" to Australia, did you find a way around this problem?
Very annoying because all but one of their fabrics are wider than 36"!
I do NOT want photographs of you lubing your tube. NO SIR!
There are many ways to get around banal US retailer exports (I have been importing for 10 years in a different arena, where 99% are longer than the regulatory 1.05cm/37"). One is to have a US friend who will receive the package and post to you (99.99999% of the time USPS could not CARE about the length of the package). Another is DHL or Fedex, though that increases the cost as USPS is still the cheapest in the USA.
I am on first name basis with Customs in QLD... they used to see me twice/thrice a month, though that has slowed down somewhat lately.
well that was easy for me, the guy from soller who I dealt with asked if I would mind if the fabric was folded in the packaging tube or not. Because the total length of my tube is around 850mm the end of the fabric will be trimmed anyway any imperfections in the cloth will not matter. I will have a good look tonight but it does not look like folding the cloth damages it. The carbon sleeves that I bought were 6 foot long and thus were folded into a tight package, this does not seem to have affected the carbon in anyway the fact is with that there is no other way of packing it.
I am especially impressed with the carbon sleeving, I will let you know how I go when I have to use it which way is easyer, but at the moment I am betting on the sleeving. It is very stretchy but it dosent stretch, weird i know but what it reminded me of is a giant cable sock (the kind that get tighter when you pull it) the fibers spread out and contract like its stretching. This gives it versatility because I bought 8 inch sleeving because it was the closest size that will fit over the mold, at 8 inches it would be too loose but if you just compact the fibers a little the diameter shrinks and it will be snug.
I hate carbon fibre, in a good way. I don't work with it much but I know how much of a pain it can be. Are you planning on vacuum bagging your mold? Folding CF won't affect it unless you crease it, CF has huge tensile strength but zero compression strength (that why we use resin) so you want to make sure that you have strands running in as many directions as possible along the longest possible path. This will make sure the loads are distributed evenly along the whole length and in all directions.
For a few things on aircraft we can design a part to be strong in one direction but weak in another, for a 'flapper valve' for example, but you don't want this in your tube so symmetry is key. Also using foam, 'air weave' or 'honeycomb' in a 'sandwich panel' structure will increase rigidity without adding much weight but will increase the bulk of the tube.
Twill looks pretty but 1x1 is easier to use over smooth shapes and cheaper, for a basic laminate I usually lay up 2(1x1)-airweave-1(1x1)-1(2x2) keeping the 2x2 as the top layer because it's 'pretty'.
It sounds like a great project, keep us updated and I'd be very interested to see pictures
I am not vacuum bagging. There is a reason for this, the plan was to make this and use it as a prototype for the future to make a larger scope the same way. I figured that while the 6 inch would be small enough to vacuum bag effectively that down the track a larger scope would not be.
I am using "peel ply" wrapped around the scope to absorb excess epoxy and hopefully keep it bubble free.
This is a few pictures of the process so far, the first is the mandrel coated 7 or 8 times with release wax. The second me lining up the first layer of 2x2 twill, and the third the first layer completed. The sleeving that I am using should impart most of the strength because it is Biaxial weaved. after laying out the 2x2 twill and measuring I should have enough for 2 layers 2x2 2 layers biaxial sleeving then another 2 2x2.
The sleeving that I am using should impart most of the strength because it is Biaxial weaved.
I may be wrong here, but I would have thought you would want all the strength to be longitudinal. If the tube is mounted in the middle, the weight of the mirror at one end, and eyepiece/camera at the other would be trying to bend the tube like a banana. The biaxial weave is at ~45deg to this axis. Considering all the strength in carbon fibre is in tension, I would have thought plain, twill or harness weave, if laid 0/90 deg to the tubes axis, would impart more longitudinal stiffness than 45 deg biaxial? To my mind, at 45deg the load is mostly carried by the filler and not the fibre?
I have also got a reply back from Jon Soller: Hi Simon,
We commonly ship FedEx to Au for packages over 40". 20 yards of spreadtow will cost approx $159 for shipping via FedEx.
If this is of interest please let us know.
Best Regards,
Jon Soller
Soller Composites, LLC
This also seems to be just slightly cheaper than the standard USPS option($233!!)
Considering all the strength in carbon fibre is in tension, I would have thought plain, twill or harness weave, if laid 0/90 deg to the tubes axis, would impart more longitudinal stiffness than 45 deg biaxial? To my mind, at 45deg the load is mostly carried by the filler and not the fibre?
I see what you mean, in any case I have 4 layers of 2x2 twill in the 0/90 orientation so the middle layer of biaxial should do no harm!
in any case I have 4 layers of 2x2 twill in the 0/90 orientation
Doh!
That will learn me for rushing to reply while at work and not properly reading your post
What wall thickness are you expecting? If you were bagging I'd say ~2mm.
I took the mandrel out tonight and gave the tube my first coat of epoxy without laminating more carbon. The tube is very strong, it took my weight over the middle without warping. It is also exceedingly light, i didnt get a chance to weigh it but it was gripable with one finger and my thumb comfortably.
I will coat the outside with around 4-5 layers of epoxy before I wet'n'dry it and put a poly urathane varnish over it. I have ordered my other parts from Orion Optics, very excited with how its going at the moment.
I have now cut the tube to length, It is quite long for its size but I wanted to protect the secondary and focuser from stray light. I am yet to wet and dry the surface and coat it with polyurathane but thats what I am doing this weekend. Orion optics have invoiced me and they quote around the 21st of November for delivery.
The two images show what the final finish should look like, and the thickness of the tube (around 3 mm)
I used west with the slowest hardener I could get my hands on. Seemed to do the trick.
Thanks! nice to know. Was it the 209 hardener you used?
I went with 207 because it starting to get warm here and the 207 has reasonable pot life(22-27min) and a decent extended working temperature(up to 32C), also it is clear setting.
I thought about the 209 because of it's very long pot life (40-50min) and it's good to 38deg, but the amber colour put me off.... If you used the 209 then I am impressed with the end result and my concerns were unfounded.
Might have to grab a bottle of the 209 too.
Did you want a 6" f/5 for it's decreased weight or what was the motivation? I just finished converting my 5.1" f/5 by adding a 2" Crayford focuser to which I attach my Sony NEX-5N MIL camera with an optional 2" GSO Barlow. The mount's unsuitable for serious tracking, but I'm going to try my hand a Lunar photography first. I kind'a wish I'd purchased a 6" f/5 myself, but we'll see if this smaller scope keeps me busy for now.
cheaper than the standard USPS option($233!!) 
