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03-10-2009, 03:48 AM
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Registered User
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Join Date: Jan 2007
Location: Gateshead
Posts: 2,205
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Carbon Composite tube upgrade questions
I've finished my Astrograph , used an offcut of 300mm NB UPVC stormwater pipe (price was right-ie free).
The resulting OTA (10" f4.66) in astrograph configuration = OAG + SSAG + 40D comes in at 21.5kg , of which 11.6kg is the tube .
I've done my RA torque balance calcs and these indicate I need another 10.5kg (=7kg + 3.5kg) of counterweights + a small adjustment weight about 13oz to move about for perfect balance about the RA pivot point.
I'd rather make the OTA loose some weight , ie scrap the UPVC and get a CCF tube to reduce the load on the gem.
My calcs indicate I can reduce my OTA mass by 6kg if I change to a CCF tube same external size and only 3mm thick , which will mean I only need an extra 7kg counterweight.
Those who did their own CCF tubes for newtonians or other fat OTAs ,
1) what were your final tube specs (OD, wall thickness, length, weight (tube alone)) ?
2) how much did it cost ?
3) where did you source the materials if you made it yourself ?
or
4) where did you buy the ready to use tube ?
Tbanks in advance.
3)
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03-10-2009, 08:13 AM
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Grumpy Old Man-Child
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Join Date: Jul 2009
Location: South Gippsland
Posts: 1,768
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I'm afraid I don't know of anyone whos made their own CF tube. I believe its fairly complicated (in execution rather than design), but I have been dealing at third-hand with an Australian company called Teakle Composites and the engineers swear by them.
Good Luck
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03-10-2009, 09:57 AM
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Like to learn
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Join Date: Jul 2007
Location: melbourne
Posts: 4,835
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I was having a look at doing a CF OTA as well.
Here is a supplier
http://carbonfiber.com.au/
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03-10-2009, 12:14 PM
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Join Date: Jan 2007
Location: Gateshead
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Quote:
Originally Posted by DavidU
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Thanks David,
That is a very handy link.
Looks like I need 12 of their standard Twill 2x2 sheets of CF (1.27m x 1m) to get approx 3mm tube thickness).
Just so happens my required CFC tube is 1.26m L x 0.315m OD . That's pretty convenient, pi * Do = 0.99m for my finished tube.
more questions :
a) I'll only need to trim about 10mm from each 1m sheet .... or would I be better off having a 10mm longitudinal overlap per "wet sheet" ?
b) how easy is it to cut unepoxyed CF sheet with a Stanley knife or sissors ?
c) Does the expoxy add anything to the thickness per sheet ? or it just a wetting / bonding agent that soaks the carbon fibres and adds nothing to the thickness per lay as such once rollered ?
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03-10-2009, 01:42 PM
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newbie
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Join Date: Sep 2009
Location: haugesund, Norway
Posts: 67
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hi
i think it is easy to cut carbonfiber before it is baked.
but if you want it hard, i think you need to wacuumpack it and bake it in certain temperature, but im not sure.
alfi
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03-10-2009, 02:20 PM
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Join Date: Oct 2004
Location: New Zealand
Posts: 4,346
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Hi Ian,
hmmmmmm, slippery slope mate, LOL.
But at 21+ kilos you really have Hobsons choice to be honest. IIRC my 10" f5 newt ready to use in a C/F tube was well under 12 kilos, probably about 11kg.
I had used "sonotube" for years, and decided to build a CF tube.
For this I used a mold of shiny Formica, rolled around a series of customwood disks, all strung on a dowel rod. The Formica I then covered with cling film "Gladwrap" is what it is known as over here. This was my "release agent".
CF matting was available, and I got about a 100mm length, which was long enough, and rolled it around the tube. That's the short version, as the long version was following advice I started with a layer of Kevlar, and that didn't really do the goods so I then used the CF on top.
A guess at the thickness would be a couple of millimeters possibly. You can accurately assess the finished weight. The cloth is a known as is the resin you use to make it stick. I would expect about 2 kilos max.
Strength? I added hoops of thin alloy strip inside the ends, and also a couple about where my tube rings were likely to be. Unnecessary possibly, but it felt better.
Cost? CF matting was about $150 per meter, resin about $50 IIRC. Lost lots of sweat though. Figure disposable gloves, masking tape, paint brushes etc. All sourced from the local fiberglass shop.
If I was to try it again I think I would peel back half the sonotube cardboard, and just CF top coat that.
There is plenty of "how-to's" on the net, but really the only way is "into it yourself".
Gary
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03-10-2009, 07:31 PM
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Join Date: Jan 2007
Location: Gateshead
Posts: 2,205
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Quote:
Originally Posted by gbeal
Hi Ian,
hmmmmmm, slippery slope mate, LOL.
But at 21+ kilos you really have Hobsons choice to be honest. IIRC my 10" f5 newt ready to use in a C/F tube was well under 12 kilos, probably about 11kg.
I had used "sonotube" for years, and decided to build a CF tube.
For this I used a mold of shiny Formica, rolled around a series of customwood disks, all strung on a dowel rod. The Formica I then covered with cling film "Gladwrap" is what it is known as over here. This was my "release agent".
CF matting was available, and I got about a 100mm length, which was long enough, and rolled it around the tube. That's the short version, as the long version was following advice I started with a layer of Kevlar, and that didn't really do the goods so I then used the CF on top.
A guess at the thickness would be a couple of millimeters possibly. You can accurately assess the finished weight. The cloth is a known as is the resin you use to make it stick. I would expect about 2 kilos max.
Strength? I added hoops of thin alloy strip inside the ends, and also a couple about where my tube rings were likely to be. Unnecessary possibly, but it felt better.
Cost? CF matting was about $150 per meter, resin about $50 IIRC. Lost lots of sweat though. Figure disposable gloves, masking tape, paint brushes etc. All sourced from the local fiberglass shop.
If I was to try it again I think I would peel back half the sonotube cardboard, and just CF top coat that.
There is plenty of "how-to's" on the net, but really the only way is "into it yourself".
Gary
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Yep , I expected the OTA to be heavyish , but when I bunged the rings (Orion UK) onto it, and put my 50mm finderscope (Lumicon), and weight it .... cripes .... !!! then I weighed the OAF with the coma corrector (both Lumicon) attached and looked up the mass of my 40D body and the Orion SSAG and added it all up ....
Worried .... and don't fancy carting all that mass about , not built my ROR shed yet ....
Add 21kg of counterweights and the Atlux on the tripod is pretty darned heavy by itself ....
Oh my .... I'll wind up either with jigantic muscles or a bad back ....
Gotta make that OTA lighter .... nothing for it .
IIRC ??
I like the idea of using gladwrap to form a barrier and I like the idea of using shiny formica to form the template , I was thinking of maybe some thin aluminium .
If the CF sheet costs $150/LM .  ... I'll put up with a the heavyweight OTA .... and put the CFC OTA tube idea on the back burner until I go up from 10" f4.66 to 15" f3.5 and start saving pennies.
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03-10-2009, 08:46 PM
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This sentence is false
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Join Date: Oct 2008
Location: Melbourne
Posts: 1,158
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To give you an idea of the weight of a typical CF tube, here are the stats from my 6" Mak-Newt I had apart recently : 1.7 mm thick, 650mm long, 175mm diameter. Weight 852g.
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03-10-2009, 09:48 PM
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Registered User
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Join Date: Jan 2007
Location: Gateshead
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Quote:
Originally Posted by Moon
To give you an idea of the weight of a typical CF tube, here are the stats from my 6" Mak-Newt I had apart recently : 1.7 mm thick, 650mm long, 175mm diameter. Weight 852g.
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I've already done some home work and calcs based on the density of 1580kg/cum for CFC and my tube , if I went for 3mm thick , 309mm ID and 1.270m long, will come it at approx 5kg.
Adding my hardware and I get a final mass of my OTA of 16kg.
A 2.2mm thick tube is 4kg , gives me a OTA of 15kg.
Desireable weight reductions , but worth the cost ??? not sure .... need to get my prices on CF sheet and epoxy and other consumeables yet to sort that out.
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03-10-2009, 09:52 PM
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Like to learn
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Location: melbourne
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Ian, don't you think 3mm CF is overkill? I would have thought 1.5 to 2mm
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03-10-2009, 10:15 PM
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Location: Gateshead
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Quote:
Originally Posted by DavidU
Ian, don't you think 3mm CF is overkill? I would have thought 1.5 to 2mm
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Well , being to new CFC tubes .... I really don't know.
2mm would be pretty good ==> my tube would be 4kg cf 11kg for UPVC
1.5mm ==> 2.5kg !! but will it be stiff enough to hold collimation and strong enough where it counts (ie where the focusor , spider and mirror cell are mounted and where the tube rings are ) ?
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03-10-2009, 10:23 PM
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Like to learn
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Location: melbourne
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Comparison of Carbon Fiber and Steel
Material Tensile Strength (GPa) Tensile Modulus (GPa) Density (g/ccm) Specific Strength (GPa)
Standard Grade Carbon Fiber 3.5 230.0 1.75 2.00
High Tensile Steel 1.3 210.0 7.87 0.17
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03-10-2009, 10:24 PM
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This sentence is false
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Join Date: Oct 2008
Location: Melbourne
Posts: 1,158
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I think 3mm is overkill too. I would aim for 2mm Max.
You could always email GSO and see if they are willing to make you a custom one.
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05-10-2009, 11:38 PM
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Location: Gateshead
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Update : progress made in my quest for a CFC OTA
I've asked Orion (UK) and they indicate the CFC tube on the AG10 is 2mm thick .... full fibre (I assume this means no honey comb "filler" , just how many layers of 2x2 Twill CF it takes to get 2mm full thickness).
Those astrographs are f3.7 which is more critical wrt collimation and stiffness is concerned than my f4.66 , so I can probably get away with about 1.8mm thickness ( ==> 7 - 8 layers of 2x2 Twill CF cloth ??).
I take it 2x2 Twill cloth is the way to go , rather than Plain or Satin (Harness style weaves) for max stuctural strength and stiffness ?
This means I can get my OTA with a CFC tube down to 14.3kg in photographic mode and 12.8kg in visual mode.
==> I'll still need one more counterweight , but not a 10.5kg one as my photographic mode torque on the scope side will fall from 7.25kgm to 5.23kgm ==> just one more 3.5kg CW to get RA balance (that's lots better !).
That's ceratinly worth seriuously considering either as subcontract job (Composite Components in Perth say they can do my tube .... I am waiting on their quote) .
If they work out too expensive (ie > $300 , I'll opt for to do this as a DIYS project if I can source 2x2 Twill CF cloth cheaply locally , will check on this tomorrow).
If I decide to do the CFC tube as a DIYS project , how thin can I go on steel or alumimium sheet to have a rigid enough mandrel to work on ?
I'm guessing I'd make the mandrel with a bit of pipe acrpss a couple of work horses , and 4 or 5 uniformly spaced plywood or MDF reinforcing forming disks (job for my jig saw ?) , wrapped in gladwrap (the Epoxy releasing agent).
0.4mm thick steel sheet stiff enough if reinforced by some mandrel disks ?
Would flexible plastic sheet be suitable to form a mandrel if it's stiff enough and cheaper than a steel sheet ?
Not ruling out using shiny formica to form my mandrel ....
When rollering the CF soaked in epoxy how much force do you need to apply to shift the excess epoxy ? Is the force requirement similar to painting with a roller brush ?
Last edited by Ian Robinson; 06-10-2009 at 01:01 AM.
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06-10-2009, 01:34 AM
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Registered User
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Join Date: Apr 2008
Location: Wynnum West, Brisbane.
Posts: 4,166
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These guys make CF astrograph tubes. Get the wallet out
http://www.dreamscopes.com/
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06-10-2009, 02:04 AM
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Join Date: Jan 2007
Location: Gateshead
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Quote:
Originally Posted by Tandum
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I looked at their site the other day .... too expensive.
Plus shipping costs of a completed ready to use CF tube will be horrendous from anywhere overseas , so that's also a deal killer.
I'll see that that mob in Perth quote .
If I buy the cloth on Ebay from the USA, I can get :
2x2 Twill 3K CF cloth 60" wide for 39USD per m + postage
plain 3K CF cloth 60" x 170" for 105USD + postage.
So this looks affordableas a DIYS upgrade if I use 4 layers of plain CF cloth followed by 2 layers of 2x2 Twill CF cloth.
Does that sound like a reasonable contruction for a 315mm OD x 1.253m tube ?
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06-10-2009, 04:03 PM
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Join Date: Oct 2004
Location: Glenore Grove Queensland
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Ian have a look at FPI Protostars blacklight tubes. 27gr/cm weight and the flocking is extreamy dark.
My 10'f3.8 Astrograph comes in at 11kgs total but that is with a conical mirror.
The 1200mm long tube weighs 3.28kg. It's very stiff and with a small amount of body filler to fill in the spirals and a nice shinny appliance enamel paint job looks a treat.
http://www.fpi-protostar.com/blite.htm
Mark
Last edited by mch62; 06-10-2009 at 04:14 PM.
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06-10-2009, 07:24 PM
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I'm still waiting on my quote for a professionally made CF tube.
I've found a place in Broadmeadow NSW ( FMS ) who can supply all the materials I need to do a DIYS CF tube including unidirectional and twill weave carbon fibre and 2 part epoxy or 2 part polyester resin.
They don't have any plain weave 3k CF cloth in stock.
I am considering the process shown in the attachment .... for making a 314mm OD x 1.27m x 1.6mm thick CF tube using epoxy resin.
The tube will be about 4kg mass.
..... how's that look ?
I've had someone at CN suggest using a layer of unidirectional CF cloth after I've done at least layer longitudinal unidirectional CF cloth. Thoughts anyone ?
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06-10-2009, 07:30 PM
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Registered User
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Join Date: Jan 2007
Location: Gateshead
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Quote:
Originally Posted by mch62
Ian have a look at FPI Protostars blacklight tubes. 27gr/cm weight and the flocking is extreamy dark.
My 10'f3.8 Astrograph comes in at 11kgs total but that is with a conical mirror.
The 1200mm long tube weighs 3.28kg. It's very stiff and with a small amount of body filler to fill in the spirals and a nice shinny appliance enamel paint job looks a treat.
http://www.fpi-protostar.com/blite.htm
Mark
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I haven't considered using a Blacklight tube .... by itself.
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