Homemade Carbon Fiber OTA Tubes?

[Bob_riggs]

I'm looking to assemble a 10", maybe a 12" short focal length Newt for richest field viewing. I plan to use this on a CG5 mount and want to keep the weight down.

I've looked all over and have found nothing in print about whether making a C/F tube is within the skill range of the average guy. Or, is it too "techie"? Does anybody know of anything available in this subject area

Thanks and Clear Dark Skies!
Bob

[Jim Fusco]

Hi Bod,

I think you will need machined rings for both ends. Maybe with a grove 1/2 to 1" deep for opening, more for mirror end.The open end ring, consider attatchment for finder there in design and maybe spider too. Capture the tube more with compression than drilling holes. Attatch mirror support to this ring. CF is not friendly to flex too much so care needs to be taken to match hardware to the tube's angle. I would also consider using a thin foam gasket between the focuser and tube. Consider using grommets, maybe machined aluminum that are threaded and gasket for the spider, and finder.
If you have a machine shop nearby, they guys usally can do side jobs for extra cash. Most machine shops are always sending stuff out to be anodized too, and could throw your stuff in the basket too.
I would suggest to wear a good mask or wet cut. I know and seen damage done to lung tissue that CF can cause.

[KenMiller]

Originally Posted by Bob_riggs

I've looked all over and have found nothing in print about whether making a C/F tube is within the skill range of the average guy. Or, is it too "techie"? Does anybody know of anything available in this subject area

It doesn't look too hard:
http://www.synapsemotorsport.com/Library/CFII.pdf

This is part I of the article above:
http://www.synapsemotorsport.com/Lib...napseCFone.pdf

[Gary Beal]

Originally Posted by KenMiller

It doesn't look too hard:

I'm with Ken. It isn't too hard, but to make an absolutely perfect work of art tube I suspect it is. My learned mate who posed this question has a motive, but lets leave that to one side for the time being.
I have always had a 10" newt, an f5 optical set that originated from Sky Instruments, which sell the Antares stuff. The mirrow was cheap, and that cheap that I bought it thinking I will have a half decent blank which I can get sorted after a few years. It is that good I hope I don't have to recoat it (I have been using it for about 8 years now), it is a stunner.
In the beginning, no folks this is not a sermon, I used it in the obligatory sonotube, and it worked well. I then thought I would try another sonotube, this time with a forimac wrap around it, partly for stiffness (not that I experienced any flexing) and partly for looks/waterproofness (again not that either had become an issue). In short I like to tinker.
This worked well, but the scales tipped at about 14 kilos or more. I also built into this later tube a set of ring baffles, about 8 of them, spaced up and down the interior, and another set of semi circumference ones across from the focuser. These baffles made an already good mirror really great, heaps of noticeable contrast etc.
Last year the tinkering bug hit again. I decided that I wanted to try something else, and after a few cell reducing beers settled on a Carbon Fiber tube. I had used fibreglass many years ago helping my father skin boats, and reasoned that it couldn't be rocket science, surely.
I built up four round wooden disks and affixed them together in a line, with the end two at the same length I wanted the tube, about 1300mm. The other two were spaced in the middle. I then made these disks able to be suspended by the ends, and rotated. making stands at each end. This allowed the "tube" to sit off the bench, and be spun slowly by hand.
Around this contraption I then wrapped a shiny formica, the benchtop stuff. This gave me something to lay the matting and epoxy to. The biggest headache with the formica was getting the edge to sit down flush, and I ended up taping it, and was still not as happy, but it was as good as I could get it.
Once I had this "former" made, the rest was easy. The forimca former was then wrapped with what we call "Gladwrap" a thin plastic food wrap, the stuff you cover food with. I figured that this would give me a release agent and avoid the formica being attached for ever to the inside of my carbon tube.
Epoxy was mixed, and plastered over the food wrap former. The carbon matting was then carefully placed on the epoxy, and this really is a challenge, as it likes to slip, slide, and twist, making the pretty pattern look awful.Once in place more resin is applied and allowed to cure off.
There is a twist to this story however as the advice given by a local supplier of this product suggested Kevlar. So I laid this first, thinking it would be all I needed. WRONG, When it cured it was pliable, and I could see problems with the flexure etc. This is why I then layered Carbo matting over the top. In the end I got a "bulletproof" tube.
Once dry and semi cured I simply trimmed the ends, and layered a thin strip of fibreglass matting on the inside, more to strengthen them. I am able to drill, and attach the F/T focuser, the spider, and the primary cell, without any issues. To finish the tube ends I used a thin rubber trim strip.
Worth it? Hell yes, the 14 kilos shrunk to about 10, and it looks better. Again this tube got baffles for Africa, and performs as good or better that the sonotube. I use the scope ina adob base, with my Argo Navis DSC's, as well as on the EM200 with tube rings. an all rounder if there ever was one.
It ain't rocket science, and equally it ain't dead simple. But if I can do it, anyone can.
Gary

[Jim Fusco]

Hi Gary,

After the Epoxy was applied, did you keep the tube roatating to keep drips from occuring? Or did you wrap the epoxy with plastic wrap. I heard of a couple of ways of doing this.

Jim Fusco

[Gary Beal]

Originally Posted by Jim Fusco

Hi Gary,

After the Epoxy was applied, did you keep the tube roatating to keep drips from occuring? Or did you wrap the epoxy with plastic wrap. I heard of a couple of ways of doing this.

Jim Fusco

Hi Jim, that was actually the funny part, I did rotate it, and it did avoid most of the drips. We got what we thought was "quick acting" epoxy, but it still took forever to gel off. If nothing else the ability to rotate was handy when applying the epoxy etc, and rubber gloves are also essential.
No pictures though, I was too busy beating the gel time.
Next time maybe.
Gary

[Jim Fusco]

Hi Gary,

The reason is I know from making fishing poles, after using epoxy on the eyes, I would leave the pole rotating for 2 days. The other I heard is using a vacume and or plastic wrap. Now with your trim ring and baffels, did you have a shop do the cutting or yourself? I like to say, you did a great job.


Jim Fusco

[Bob_riggs]

Gary, I certainly agree with Jim. You did a fine job, indeed! Jim mentioned the need for end rings for support. Do you feel they would be helpful, or is your tube sufficiently rigid?

Jim, thank you for your input, and suggestions.

Ken, the article you shared along with Gary's encouraging success story is just what I needed. Making a female mold is something I had not considered. And, there is a lot of good information in it which I, and others, will find most helpful.

It sounds very "doable". Thanks, guys!

Clear Dark Skies!
Bob

[KenMiller]

Here's a forum that looks like they have some folks that know what they are doing that are willing to answer questions and make suggestions:

http://www.fibreglast.com/VBulletin/

[Bob_riggs]

Thanks again, Ken. This looks to be a very good forum to explore this subject area. How do you come up with this stuff, anyway...lol?

CDS!
Bob