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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Want it stiff , and able to support my spider , 2" crayford with 2kg of gear on it , the all aluminium cell and take some compression and shear from the tube rings.
Want it as light as possible while at least as strong as my UPVC tube and rigid.
I'm thinking 2mm - 3mm wall thickness in 2x3 Twill CF and epoxy.
What's the recommendation of people who have done their own CF newt tubes or bought commercial CFC tubes ?
Anyone know how thick the CFC tubes are on Orion (UK)'s 10" astrographs ?
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mark Jimenez
sage
Reged: 01/08/07
Posts: 339
Loc: Atlanta GA.
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Hello Ian, Hopefully someone with more experience will answer as well, but from my experience, for a truly stiff tube, you should consider at least six layers of 6 oz cloth. I would also reccomend two of those layers be uni-directional cloth. One with the fibers oriented the lenght of the tube and the other, 90 degs, or radially. When I built my tube, I added this layer of uni-directional fabric with the fibers going around the tube on the front half to support the focuser and it was amazing how much stiffer this made the front of the tube.
Just my 2 cents, hope it helps.
-mark
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Celestron ASGT
Astro Tech 8" f4 Newt
QHY8
Meade DSI pro
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PrestonE
Pooh-Bah
Reged: 04/29/05
Posts: 1170
Loc: Houston,Texas
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Hello Ian,
For what you want to do you really could do this with a core material or not...
It is the inter and outer layers that give the overall stiffness...the inter layers are just a filler.
You can increase the radial stiffness by wrapping unidirectional around the outer diameter for several layers...the hoop strength will increase dermatically...after just a few layers...
For the lightest weight, I would look at a couple layers of uni going the lenght of the tube, wrapped with uni balsa in the same direction and then uni on the OD going lenghtwise...
Do your reinforcements radially around the OD at the ends and mounting points...
This will produce a very light and stiff structure and a minumal cost... 
Best Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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mak5
member
Reged: 03/09/09
Posts: 22
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The problem for sandwich construction is that is necessary to use vacuum consolidation to bond the core to the skins perfectly. It can be done but it takes a little time to get it right.
For radially reinforced zones, I would also add a couple of +-45° biaxial because usually in those areas there are some holes drilled.
As PrestonE said, the structure will be very light and strong. But I get the feeling that you're also after the "carbon look", so you can wrap a ply or two of carbon twill on the outside diameter. It will look "cooler" at the cost of introducing interlaminar and free-edge stresses.
Edited by mak5 (10/05/09 02:01 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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I decided to ask John at Orion (UK) what CFC tube thickness they have on those nifty astrographs of theirs, the AG10 in particular.
He says 2mm .
Looking at the images they look like 2x2 Twill CF.
Fast astrograph newts need very rigid tubes at < the f4 so 2mm will probably be a bit over engineered for my f4.66 , so I'll likely opt for 1.8mm thick in 2x2 Twill Weave CF , can probaby get away with 1.5mm thick in 2x2 Twill CF CF , and if it's not stiff or rigid enough, add another layer or two of 2x2 Twill CF as later to the same tube.
If that even possible ?
(in that case the disassembled OTA becomes the mandrel).
How's a 1.5mm thick CF 315mm OD x 1.253m for a 10" newt sound ?
I'd only need an extra 3.5kg CW rather than 10.5kg of extra counterweights to balance the system.  Now if only the quote for the tube is cheap enough , if not , if the materials are cheap enough to make this affordable as a DIYS upgrade.
Edited by Ian Robinson (10/05/09 10:29 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Quote:
The problem for sandwich construction is that is necessary to use vacuum consolidation to bond the core to the skins perfectly. It can be done but it takes a little time to get it right.
For radially reinforced zones, I would also add a couple of +-45° biaxial because usually in those areas there are some holes drilled.
As PrestonE said, the structure will be very light and strong. But I get the feeling that you're also after the "carbon look", so you can wrap a ply or two of carbon twill on the outside diameter. It will look "cooler" at the cost of introducing interlaminar and free-edge stresses.
Prescot and Mak,
Are you saying to use the 2x2 Twill for a couple of outer layers to finish off , and to do the under layers in plain weave ?
Reinforcing with an extra layer of 2x2 Twill where the mirror cell and spider and focusor are ?
How does using cheap but very shiny formica as the surface for the mandrel sound ?
And wrapping that in clingWrap or GladWrap (to permit easy release from the mandrel when done) ?
Edited by Ian Robinson (10/05/09 10:43 AM)
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paul11
professor emeritus
Reged: 01/30/06
Posts: 576
Loc: Essex UK.
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Hi Ian, you say you want the tube to be as light as possible, what is the maximum you want it to weigh ( approx ).
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LX90-10" Canon 350D Toucam 840K Barn-door tracker
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mak5
member
Reged: 03/09/09
Posts: 22
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I was talking about UD (unidirectional carbon fiber) and biaxial +-45° (wich is made of two UD layers stiched together).
Twill is a weave so the fibers go above and under other fibers, making them "wavy". A twill structure is not as stiff as an UD composite. The UD composite (depending on the orientation of the fibers) will have a lower thermal expansion coefficient.
If you want the strongest and stiffest structure, UD and biaxial is the way. Of course, twill looks better on the finished part, but it wouldn't be as stiff.
As for the 1,5mm thickness, maybe you can get away with some UHM (ultra high modulus) unidirectional (wich is very expensive). A more efficient structure will be a sandwich as PrestonE said also, but the thickness will be bigger than 1,5mm.
The best mandrel will be an aluminium one wrapped in mylar (or you can use nylon depending on the cure temperature). At temperature, the aluminium mandrel will expand, tightening everything wrapped on it.
Provided that you can make the formica mandrel cylindrical and stiff enough, I think it will work.
When releasing the tube from the mandrel, pull on the mandrel (and fix the tube on the closest end to the pulling end of the mandrel), not the tube. If you pull on the tube, the tube will "hug" the mandrel even tighter because of Poisson ratio of the composite.
Edited by mak5 (10/06/09 03:02 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Quote:
Hi Ian, you say you want the tube to be as light as possible, what is the maximum you want it to weigh ( approx ).
I have no aim mass for the tube , I am more interested reducing my tube's mass as much as I can (for convenience) and still having a tube that is stiff and strong and which will hold collimation.
Edited by Ian Robinson (10/06/09 03:08 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Quote:
I was talking about UD (unidirectional carbon fiber) and biaxial +-45° (wich is made of two UD layers stiched together).
Twill is a weave so the fibers go above and under other fibers, making them "wavy". A twill structure is not as stiff as an UD composite. The UD composite (depending on the orientation of the fibers) will have a lower thermal expansion coefficient.
If you want the strongest and stiffest structure, UD and biaxial is the way. Of course, twill looks better on the finished part, but it wouldn't be as stiff.
As for the 1,5mm thickness, maybe you can get away with some UHM (ultra high modulus) unidirectional (wich is very expensive). A more efficient structure will be a sandwich as PrestonE said also, but the thickness will be bigger than 1,5mm.
The best mandrel will be an aluminium one wrapped in mylar (or you can use nylon depending on the cure temperature). At temperature, the aluminium mandrel will expand, tightening everything wrapped on it.
Provided that you can make the formica mandrel cylindrical and stiff enough, I think it will work.
When releasing the tube from the mandrel, pull on the mandrel (and fix the tube on the closest end to the pulling end of the mandrel), not the tube. If you pull on the tube, the tube will "hug" the mandrel even tighter because of Poisson ratio of the composite.
Now the October longweekend is over, I called a local place that sells fibre and carbon fibre products and materials (mostly for the boaties and car enthusiasts).
They suggested in our climate a carbon fibre tube will get really hot (maybe 80oC) if exposed to direct sunlight in summer which will effect stability if I use epoxy resin to bond the CF.
They suggested I would be better off using vinyl ester epoxy instead which is easier to work with and more thermally stable.
Views on this wrt a telescope tube please ?
The scope will be stored in the garage until my permanent ROR shed is made so I don't really need to worry about the tube getting hot.
If I take it anywhere in the car, I'll just toss a sheet over it to keep the sun off.
They also suggested I use unidirectional CF cloth applied longitudinally to make the tube very resistant to bending.
Also suggested as a cost saving to, after the unidirectional CF cloth layer was in place , to apply 10oz fibre glass as a layer and then to cover this with 2x2 Twill 3k CF cloth. I'm not so sure about a filler layer of fibre glass, since Orion UK say their tubes are all carbon fibre.
I've come up what I propose to do : see attachment . Using EPOXY resin. How does that look as a process for making my tube , and will it be strong/ stiff enough ?
I think the CF cloth is about 0.23mm thick (>> ?? <<) , and 180g/sqm.
To get about 1.5mm thickness , I need 7 layers of CF ==> 1.6mm thickness , close enough ==> 3kg tube..
Re biaxial 3k CF , this is 2 cloth thicknesses ?? , would it be worth while substituting a layer of plain weave cloth with biaxial 3k CF cloth ???
Edited by Ian Robinson (10/06/09 09:22 AM)
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mak5
member
Reged: 03/09/09
Posts: 22
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I cannot see the attachment.
They are right, carbon fiber and sun do not get well together. You could use some higher temperature epoxy or some high temperature vinyl ester resin but if you only apply clear varnish on the tube you will still have the UV degradation of the composite.
If you plan to use a mix of carbon and fiberglass you will end up with a structure made of fiberglass with some carbon fiber wich will be heavier, thicker and not as stiff. But it will be cheaper.
As an alternate solution, try using some basalt UD instead of carbon. It will be cheaper than carbon and stronger than fiberglass. The downside is that basalt is three times less stiff than carbon.
If the tube's main design condition is weight, then your calculations are correct for a 50% carbon/resin mass ratio but this doesn't mean that your tube will not bend or change shape. Also, with hand lay-up and without vacuum consolidation, it will be difficult to get to the 50% mass ratio. The more resin you have in the final part, the lower the stiffness and strength.
Try at first to make some smaller tubes from fiberglass and epoxy or vinyl ester resin and then begin the construction of the big tube. In the mean time, read everything you can find about composites.
This beeing said, if I were making a tube, I would make a sandwich structure with the skins from UD and biaxial (on the relevant areas) and a nomex honeycomb or foam core. It will be lighter, stiffer and cheaper than a non-sandwich structure. The downside is that it will be more difficult to make.
As for Orion Optics, I think they use some honeycomb or foam as a core and the skins are carbon. They described the production method for their tubes some time ago on their website.
Edited by mak5 (10/06/09 04:26 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Mak
I forgot to add the attachment. Can you see it now ?
Also is this http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110441913510&ssPageName=ADME:X:RTQ:GB:1123 the material you were referring to as Quote:
UD (unidirectional carbon fiber) and biaxial +-45° (wich is made of two UD layers stiched together)
?
The supplier says its 1.1mm thick , and very high strength 12k compared to 3k for the other CF products I've been looking at (unidirectional , plain and 2x2 twill weave).
They say it's constructed as
Quote:
PLY CONTRUCTIONS
0° SUPPORT THREAD
FIBRE SPECIFICATION E-GLASS YARN
FIBRE TEX 68TEX
GAUGE 0.5
PLY WEIGHT 1.5GSM
-45° PLY
FIBRE SPECIFICATION HIGH STRENGTH 12K
FIBRE TEX 800TEX
GAUGE 4.5
PLY WEIGHT 200GSM
90° SUPPORT THREAD
FIBRE SPECIFICATION E-GLASS YARN
FIBRE TEX 68TEX
GAUGE 0.5
PLY WEIGHT 1.5GSM
+45° PLY
FIBRE SPECIFICATION HIGH STRENGTH 12K
FIBRE TEX 800TEX
GAUGE 4.5
PLY WEIGHT 200GSM
, so would his count as by first 2 layers (then 0o and 90o 3K unidirectional CF ) and the multidirectional layer you suggested ? but ... E-Glass is not CF , but fibre glass , so lower spec .... so I not same as 0o unidirectional 3k CF + 90o unidirectional 3k CF + biaxial +- 45o 3k CF as far as I can see.
Where can I get +-45o 3k CF laminated CF ?
Twill is a weave so the fibers go above and under other fibers, making them "wavy".
Edited by Ian Robinson (10/06/09 09:41 AM)
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mak5
member
Reged: 03/09/09
Posts: 22
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The biaxial in your example is too thick. The more fibers you have in one direction, the stiffer the part is in that direction and less stiff in other directions..
I will give you an example of tube I would make. The skins' layup must me symmetrical regarding the skin's midplane to avoid internal tensions and asymetrical bending and deformation.
I would choose an aluminium mandrel that I would wrap in mylar or nylon very tight.
After that, I would wrap very tight two layers of HM carbon UD (like this one: http://shop.r-g.de/en/Reinforcement-fabrics/Carbon-inlay/Carbon-non-crimp-fabric-HM-100-g/m-unidirectional.html) with the fibers along the tube's length. After that, at the tube ends and in the area of the rings (you will drill holes in those areas), I would wrap a layer of biaxial +-45° (like this one: http://shop.r-g.de/en/Reinforcement-fabrics/Carbon-inlay/Carbon-non-crimp-fabric-100-g/m-biaxial.html) with the fibers oriented at +-45° with the tube's length. In those areas only I would also wrap a layer of UD like the first example at 90° with the direction of the tube. After that, another biaxial layer only in the areas mentioned above and then two layers of UD going along the tube's length.
Wrap it in peel-ply and then in a heat shrinking tube or nylon foil and cure it (preferably at temperature). This is the first skin.
Remove the peel-ply and then wrap very tight a layer of 3mm Airex foam (like this one: http://shop.r-g.de/en/Sandwich-materials/520103-1-1500-x-540-mm-thickness-3-mm-weight-of-sheet-c-194-g-1.html) with the ends bonded together and then vacuum bag it.
After that, put another skin on the mandrel and cure it.
The finished tube will not have an estethic finish like a twill does but it will be very stiff and light. The thickness will be around 4mm. Depending on the fiber volume ratio, you can end up with a tube of some 1,5kg.
In the suplementary reinforced areas you will also have a bigger thickness (about 0,3mm of difference).
Beware that it takes a lot of work to do this and the cost is high too. You can replace the carbon with E-glass or basalt UD and biaxial.
The best bet is to make some smaller diameter tubes at first (80-100mm diameter) and then big tube.
In composite manufacturing mistakes can be very costly because you will have to throw away the part, you cannot re-use it.
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