Carbon Composite tube upgrade questions

[Ian Robinson]

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)

[Waxing_Gibbous]

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

[DavidU]

I was having a look at doing a CF OTA as well.
Here is a supplier
http://carbonfiber.com.au/

[Ian Robinson]

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 ?

[alfi]

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

[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

[DavidU]

Probably the best way is to look at these 2 part videos.
http://www.youtube.com/watch?v=LjU5hVTtdzU

[Ian Robinson]

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 .... :eyepop:

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 ....

:help:

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 .:eyepop:... 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.

[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.

[Ian Robinson]

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.

[DavidU]

Ian, don't you think 3mm CF is overkill? I would have thought 1.5 to 2mm

[Ian Robinson]

\

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 ) ?

[DavidU]

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

[Moon]

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.

[Ian Robinson]

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 ?

[Tandum]

These guys make CF astrograph tubes. Get the wallet out :)

http://www.dreamscopes.com/

[Ian Robinson]

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 ?

[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

[Ian Robinson]

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 ?

[Ian Robinson]

I haven't considered using a Blacklight tube .... by itself.

[DavidU]

Ian, to make the focus area stiffer why not do a few more wraps about 5" wide around the ota where the focuser is fitted?

[Ian Robinson]

That's probably a good idea , I was thinking a good idea is to stiffen the tube where the cell is bolted on, where the focusor is and where the spider bolts on by applying at least one extra layer of unidirectional CF with the fibres orientated parallel with tube circumference , this will I think enhance hoop strength and make the tube extra resistant to deformation and compression in those sections (ie the bottom 300mm , the top 300mm and maybe once I've got the new DEC torques sorted (for the DEC balance) do something similar for where the two tube rings compress the tube.) .... cripes my tube will only be 1.27m long , and if I don't cut the unidirectional CF cloth circumference reinforcements , then I may as well just do the whole length of the tube in 2 layers of 0o unidirectional on top of the first 90o layer of unidirectional ....

This sound right ?

[Tandum]

These are pretty cheap and worth a look but they say they will not ship outside the US. How do we get our hands on one?

[Ian Robinson]

mch62

What are the Outside and inside diameters of your blacklight tube from Protostar ?

Have you checked how it holds collimation by observing how collimation shifts when you move the tube about and into different orientations (via a laserbeam type collimator) ?

[Ian Robinson]

Tandum,

I asked Protostar about getting hold of a 1.27m x 12" BlackLite tube and have been informed the shipping will be 180USD.

Too bad no one here in Australia stocks them (hint ... hint ... any retailors reading this as this is what the response was -



Unfortunately my tube needs to be 50" long.

[Ian Robinson]

I asked Composite Components , Bibra Lake, Perth for a quote to make my 314mm OD , 1.7mm thick CF tube , they estimate about $1000. Scrub getting the tube made by them .

Will likely source my unilateral 3K CF cloth, and plain or 2x2 twill weave 3K CF cloth and 2 part epoxy , make my own mandrel and have a crack at making my own CF tube.

In the meantime while I'm sourcing my raw materials , I've queried Vixen Japan re how well the New Atlux servos will cope with my 7.25 kg.m RA tangent arms eithe side of the RA pivot point (assuming I stick with my heavy OTA tube and buy 10.5kg of extra counterweights).

[mch62]

When i got my 46"x 12" blacklight tube back about 12months ago i don't remember it being $180 for shipping ?? But I went for the Blacklight tube because it was the most economical lightest and least messing around & quickest compared to making a CF tubes. I have made them before as well as FG ones.
The cost of $115 for the tube and remember this is pre flocked + say $180 for shipping is still a resonable price. When I got quoted the shipping it was for the tube boxed + what ever fitted inside the tube for transport so I got a secondary , spider and heated secondary holder end caps trims and a couple of meters of the extra blacklight cloth for future projects.
Add a mirror and focuser and presto a Telescope.
I think if you need it longer that is when they won't ship outside US ???
As far as stiffness goes holding collimation when moving from horizon to horizon no problems there. The tube is very stiff and not prone to squashing. Actually much stiffer than steal or aluminium tubes for the weight/thickness ratio.
It has the feel of a CF tube.
I am using a Conical mirror which reduces overall weight and means the mirror does not need to be colliminated once originally done , only the secondary as required. Also at f3.8 thermal expansion appears to be quite low and have found refocusing to be minimal over a coarse of a night.
I only wish they made tubes to suit larger mirrors although i would most probably go a double truss again for larger mirrors.
I experimented with my Green laser at different angles and different materials and paints as well as the inside of the Blaclight Tube and the BL flocking gives the least light scatter I could find. :thumbsup:
Mark

[mch62]

P.S. Ian I have to eventually cut 3" off the bottom off my tube ,you can have that + 46" only 1" short:rofl:
Mark

[Ian Robinson]

Thanks Mark,

That was interesting and useful information , I'll keep that in mind, expectally now the AUD is getting better.

I can probably shorten my tube requirement by a few inches if push comes to shove.

I've not bothered shortening the threadbar that holds the secondary holder (maybe 3" there) , kept it as the extra bit of tube beyond the focusor helps keep stray light out and maybe a bit of dew.
But being a "skinnyer" tube , my focusor will be closer to the primary so I'd need to move the primary further away from the secondary.... need to model that to work out how far.

I've had a quote from company in China for some unilateral 12k CF, plain and 2x2 twill 3k CF which is 230USD including postage for enough for 4 layers of CF.
Just a matter deciding on how to make a mandrel , $70 for some thin polycarbonate from Specialised Wholesale (Lambton NSW) , getting a quote for aluminium tube (1.6mm thick sheet rolled to a tube = 5.28kg) a possible alternative OTA tube (?).

Enough Protostar SA flock to do the entire inside of the aluminium tube or a carbon fibre tube , 80USD.

2 litres of 2 part acrylic to make the carbon fibre tube $49 from FMS (Broadmeadow NSW).

[AlexN]

I'd love to move my 80mm F/6 objective into a carbon fiber tube... Would make a difference both in thermal expansion (focus drift due to temperature) and also reduce the weight of the scope... I would love to do it..

[Ian Robinson]

Woudn't cost much to do the CF tube for a 80mm refractor.

Wouldn't need much 12k unilateral or 3k 2x2 twill cloth and not a lot of epoxy.

The 12k unilateral cloth comes 300mm wide.
The 3k 2x2 twill cloth cames 1m , 1.27m or 1.5m wide.
You can buy small lots on Ebay (I need more than a 12" long or 1m long sample, and I've not seen unilateral cloth on Ebay unfortunately).