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Old 01-10-10, 06:40 PM   #1
meech151 
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Making Carbon Tubes

I am wondering what is the best method to make a carbon tube, what to use for a mandrel and how to get the finished tube off. I have searched for styrofoam tubes on the internet with not much luck, can't believe it. I just made a fiberglass tube over a waxed steel tube with holes drilled all in it and thought that hitting it with some air pressure might loosen it, it won't budge as it is. I also tried parchment paper on my first attempt and it didn't work either, although after I cut it off the steel tube the parchment peeled right off of the fabricated tube. Does anyone have a proven method? It would be greatly appreciated.
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Old 01-10-10, 07:18 PM   #2
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Wouldn't it be easiest to make styrofoam forms of the size and shape you want rather than being restricted to simple tubes?
Then you can just melt the foam out.
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Old 01-10-10, 08:00 PM   #3
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I haven't had much luck finding styrofoam tubes on the internet if you can believe it. On certain parts you are definitely gonna have to cut some styrofoam, stays and such, however I didn't want to have to make every tube out of styrofoam b/c you are gonna spend alot of your time just shaping the styrofoam mold. The sizes of the tubes are not an issue, you can find just about any size steel tube you would need to make a carbon one, more so than styrofoam, and I guess you can make different styles of tubes but the round tube would be the most versatile. It would be nice to have a reusable mold.
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Old 01-10-10, 08:37 PM   #4
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I'm not sure it would take THAT long to shape a piece of styrofoam. I think I'd rather have the capability of ovalizing or making the shapes more aero than just perfectly round tubes.
If you're set on a round mandrel then perhaps Teflon or Delrin rods would be the best for slipping the carbon tube off.
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Old 01-10-10, 08:48 PM   #5
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http://www.mavcoatmoldrelease.com/ca...ldrelease.html
These guys sell a product called Mandrel Release. Kick an email off to them.
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Old 01-10-10, 08:57 PM   #6
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How about this:
  1. Get a cardboard tube
  2. Paint the outside of the tube to build up a smooth surface
  3. Do your layup over the tube
  4. After the resin has cured, soak the cardboard with water
  5. When the cardboard softens, take it out
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Old 01-10-10, 09:27 PM   #7
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i might suggest finding some precision ground shafts, and polishing as nice as you can. then find some mold release wax, and wax the crap out of the tubes. layup carbon over the polished, waxed shafts, and let cure. from there, drill a hole in a aluminum plate that is just larger than the OD of the polished shafts. cut the carbon around the tube off to create a flat end of the carbon tube. insert metal tube into the hole in the aluminum plate. a few swearwords later, and the use of a hydraulic jack(pulling works better than pushing) you should have a carbon tube and a metal mandrel. rinse(not literally, wax again) and repeat.

worked for me anyways.

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Old 01-11-10, 01:15 AM   #8
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Is there any sort of inflatable form available?
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Old 01-11-10, 07:44 AM   #9
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There are some good ideas, I am just gonna have to try and see what works. I checked out the Maverix mold release and am gonna call them. I found some styrofoam tubes in 1 1/2" OD. The cardboard tube theory is interesting, I was also thinking about using those plastic tubes that golfers put their clubs in, not sure how heavy they are. Another idea I had was to have a steel tube, or any kind really, drill a bunch of holes in it, seal on end off, lay up the carbon, and when it has cured hit it with air pressure or possible water to see if that breaks it free. Does this sound feasible? I have always heard about frame companies using bladders/balloons to make carbon tubes, don't know anymore than that. I was and probably still am gonna buy some tubes from Edge Composites, he has a pretty fair price on them, and in the long run is probably the most efficient but now I am on a mission to make my own.
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Old 01-11-10, 08:25 AM   #10
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I doubt that is feasible for a couple of reasons. The holes will allow epoxy to "key" into which will tend to lock the two together even if you do manage to loosen the rest of it. Another factor is that carbon is essentially non expanding. I think it will hug the mandrel too tightly to allow anything to crack it free.
Think of a carbon wrapped scuba tank. They hold in up to 5000 psi of air without showing perceptible outward flex.
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Old 01-11-10, 06:13 PM   #11
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Quote:
Originally Posted by Canaboo View Post
I doubt that is feasible for a couple of reasons. The holes will allow epoxy to "key" into which will tend to lock the two together even if you do manage to loosen the rest of it. Another factor is that carbon is essentially non expanding. I think it will hug the mandrel too tightly to allow anything to crack it free.
Think of a carbon wrapped scuba tank. They hold in up to 5000 psi of air without showing perceptible outward flex.
Exactly. And the rigidity of the carbon fiber layup works against you here.
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Old 01-11-10, 06:14 PM   #12
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Quote:
Originally Posted by meech151 View Post
There are some good ideas, I am just gonna have to try and see what works. I checked out the Maverix mold release and am gonna call them. I found some styrofoam tubes in 1 1/2" OD. The cardboard tube theory is interesting, I was also thinking about using those plastic tubes that golfers put their clubs in, not sure how heavy they are. Another idea I had was to have a steel tube, or any kind really, drill a bunch of holes in it, seal on end off, lay up the carbon, and when it has cured hit it with air pressure or possible water to see if that breaks it free. Does this sound feasible? I have always heard about frame companies using bladders/balloons to make carbon tubes, don't know anymore than that. I was and probably still am gonna buy some tubes from Edge Composites, he has a pretty fair price on them, and in the long run is probably the most efficient but now I am on a mission to make my own.
You might get some ideas from doing a Patent search...
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Old 01-11-10, 06:37 PM   #13
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places that make architectural foam, can make shapes that you could use. a lot of those places also do letters for signs. they can do whatever shape you want that has a single cross-sectional shape as they cut the shapes with a large CNC hotwire cutter
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Old 01-11-10, 11:52 PM   #14
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Slightly tapered mandrels? Carbon tube comes off from the smaller end.
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Old 01-12-10, 03:50 AM   #15
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Quote:
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I doubt that is feasible for a couple of reasons. The holes will allow epoxy to "key" into which will tend to lock the two together even if you do manage to loosen the rest of it. Another factor is that carbon is essentially non expanding. I think it will hug the mandrel too tightly to allow anything to crack it free.
Think of a carbon wrapped scuba tank. They hold in up to 5000 psi of air without showing perceptible outward flex.
Worse, the epoxy shrinks slightly as it cures, making the final size of the tube ever so slightly smaller than the staring ID/OD.

Carbon-wrapped tanks are very thickwalled though. Their sectional aspect ratio is much larger than a bike tube wrap. I'm going to go with the shrinking rather than the perceieved stiffness being the controlling issue here. More lube! :-)
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Old 01-12-10, 06:35 AM   #16
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Will epoxy not melt styrofoam? How do people make molds out of foam without it eating it up, are they wrapping it with something? It definitely ate through my plastic cups. A friend of mine who is an engineer said its not so complicated to make a carbon frame but its more difficult for an amateur to make one and get all the qualities out of it that it is desirable for, lightweight, strength, stiffness, etc. He basically said my steel frames would probably be as light and alot stronger than any carbon frame I could make on my own. I was curious if anyone here has produced a carbon frame that lived up to all your expectations?
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Old 01-12-10, 07:10 AM   #17
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I'm pretty sure carbon wrapped tanks are actually thin walled. I think the whole point of that is to make the tank as thin and light as possible.
Epoxy melts foam and plastic to a degree because it generates heat as it cures rather than through it "eating" the material. That(heat) isn't a problem when it is spread in a thin layer in a lay-up.
Almost every other composite application actually leaves the foam core in place.
If you check out the foam types available from Aircraft Spruce they range from basic styrofoam to more advanced forms, all Epoxy compatible.
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Old 01-12-10, 06:23 PM   #18
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The simplest way to make a carbon tube is to wrap light glass around a waxed aluminum tube, and wet it out with epoxy. then you use a knife and slice it end for end so that it is free to come off. Then you re-wax and reapply the glass, and build up your carbon tube, then you slide the whole mess off. The inner sleeve will not contract enough to grip the tube, or you could spot weld it with some 5 min. Probably too much parasitic weight for the average bike app. Works great for stuff like spinnaker poles.

There are a lot of instructions on alternative methods online. One involves ironing a thick layer of wax over a tube, then wrapping it with cellophane so that the tube will release the carbon tube built over it.

Epoxy does not melt foam. Many composite structures use foam cores. Even Dow insulating blue foam is happy around epoxy. The foam can be cut with a wire saw, the carbon built over it and then the foam can be melted out with acetone.

Carbon tubes are readily available though, and it probably doesn't pay to make your own in the smaller sizes. Also getting the best yield so that your tube has the correct balance of structural properties is something that can make it difficult, since you will require efficient building techniques like vac bagging, and a variety of very light carbon cloths for linear and hoop strengths. When it comes to making larger tubes it can save a lot of money, with the result that it is undertaken for sailboats and gliders by some builders.

Check out youtube for some vids.
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Old 01-13-10, 06:34 AM   #19
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How are the big companies making their frame parts, for example, their square chain stays or their wishbone seat stay or just some intricate tube design? Do they have someone producing multiple styrofoam molds or are they using a different method?
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Old 01-13-10, 12:13 PM   #20
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I remember reading a post a while back, I am pretty sure it was here, but I can't find it now. Anyways, they suggested using aluminum tubing as a mandrel. After the carbon is all cured and ready packing the tube with dry ice to shrink it. The idea is that since carbon is not as sensitive to hot /cold as the aluminum the mandrel would shrink enough to slide right out of the new carbon tube. I wish I could remember what thread that was under to credit the idea. Seems like it would work given the properties of the metal versus the carbon.
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Old 01-13-10, 04:10 PM   #21
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there are a lot of options for bias weave materials, inflatable mandrels inside female molds etc.. Where it gets difficult is making nice accurate parts with very tight fiber geometry.

http://epoxyworks.com/26/index.html
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Old 01-19-10, 10:08 AM   #22
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have a look at this thread - everyone has a different way of doing things but this one works well

http://www.rcgroups.com/forums/showt...1000547&page=2
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Old 01-20-10, 08:52 PM   #23
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http://videos.howstuffworks.com/scie...ames-video.htm

i saw that recently on how its made. the only problem though is i am assuming those carbon fiber sheets they're using are some sort of carbon fiber weave with a thin layer of heat activated epoxy over them. (readily available ?)

PS im not a frame builder, but i love engineering, problem solving, and science
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Old 01-20-10, 09:17 PM   #24
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It's this a little like a normal builder making his own tubeset? If you're dealing with circular cross-sections, why not just buy the tubes?
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