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Any carbon builders in this forum?

Old 06-25-13, 11:13 AM
  #1  
reddog3
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Any carbon builders in this forum?

I'm looking for answers and material- I build my own (steel) frames and am looking to put a carbon insert in the head tube.

Here's the deal- The headtube ID is 44mm. Short of sourcing a custom CF tube (which wouldn't be economically feasible) I've found a tube from Rockwest Composites that is close, and if formed to the bottom end of their spec would provide for a sufficient bondline.

I suppose I could ask them to measure their stock and provide the smallest OD, but I imagine that won't happen. So the question is- is it feasible to sand, grind or turn the OD to reduce the diameter .005" or so, without running into finishing issues. I'm not concerned about the integrity of the tube (it won't be affected) just the finishing. These are the tubes in question- http://www.rockwestcomposites.com/br...-carbon-tubing

Second question- are the other sources for tubes a guy like me can buy from? I'm a hobbyist builder with very little volume so someone like Enve is not interested. I've checked all the sources I could come up with, and no one but Rockwest comes close to the size needed.

Third and final question- Are there any carbon builders out there who have stock, or could source, that would sell me the appropriate tube in 1 foot lengths or so?

Thanks- RD
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Old 06-25-13, 11:33 AM
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I keep thinking I would like to build with carbon, but I've been thinking that since about 1980, so I'm not sure it will ever happen.

I don't see why you can't take down the carbon other than it's going to be hard to finish the loose ends that will most likely result. You might have to go farther than you originally planned. I think I would probably try to make the hole bigger, one way or another.
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Old 06-25-13, 12:00 PM
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Could you more accurately describe how this insert is going to be positioned? I think it would be easier to form your own insert depending on exactly what you mean by this of course.
Carbon actually generally "machines" pretty well. It's not as prone to fraying as people seem to think.
I routinely chop up carbon seatposts for various uses and enlarge the inside or reduce the outside.
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Old 06-25-13, 02:02 PM
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Unterhausen- can't make the hole bigger or else I'd have to build the ID back up in the headset seats.

Canaboo- A portion of the headtube will be cut away and the CF insert will be reinforcement, and I like the aesthetic. I sure as hell ain't the first to do this- I'm just copying. Here's one example- http://www.englishcycles.com/wp-cont...s_007_2557.jpg.

Another thought I had was to build a "female" mold and pressurize internally with a bladder. But for one or two uses, doesn't seem worth the effort. Would be fun though- so who knows. Just might give it a go. CF s expensive anyway so what's a few more bucks for a form?
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Old 06-25-13, 04:17 PM
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Originally Posted by reddog3 View Post
Unterhausen- can't make the hole bigger or else I'd have to build the ID back up in the headset seats.

Canaboo- A portion of the headtube will be cut away and the CF insert will be reinforcement, and I like the aesthetic. I sure as hell ain't the first to do this- I'm just copying. Here's one example- http://www.englishcycles.com/wp-cont...s_007_2557.jpg.

Another thought I had was to build a "female" mold and pressurize internally with a bladder. But for one or two uses, doesn't seem worth the effort. Would be fun though- so who knows. Just might give it a go. CF s expensive anyway so what's a few more bucks for a form?
Thought it would be something like that. The easy solution is to cut out the portion you want and then rough up and clean the inside of the HT. Lay the carbon of choice inside and then pressurize with an inner tube bladder with the cut ends knotted tightly.
You'll get a nicer fit and you can monitor the expansion of the bladder through the "window" and finesse the resin saturation through the carbon. You may have to control it from ballooning through the gap with an external wrap depending on how much the inner tube distorts with pressure. If you use a thick inner tube with little pressure requirement it will be easier to control that.
Doing stuff like this "in situ" will give you a more precise fit and bond.
You can pull the inner tube out fairly easily.
"
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Old 06-25-13, 06:26 PM
  #6  
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Originally Posted by reddog3 View Post
I'm looking for answers and material- I build my own (steel) frames and am looking to put a carbon insert in the head tube.

Here's the deal- The headtube ID is 44mm. Short of sourcing a custom CF tube (which wouldn't be economically feasible) I've found a tube from Rockwest Composites that is close, and if formed to the bottom end of their spec would provide for a sufficient bondline.

I suppose I could ask them to measure their stock and provide the smallest OD, but I imagine that won't happen. So the question is- is it feasible to sand, grind or turn the OD to reduce the diameter .005" or so, without running into finishing issues. I'm not concerned about the integrity of the tube (it won't be affected) just the finishing. These are the tubes in question- http://www.rockwestcomposites.com/br...-carbon-tubing

Second question- are the other sources for tubes a guy like me can buy from? I'm a hobbyist builder with very little volume so someone like Enve is not interested. I've checked all the sources I could come up with, and no one but Rockwest comes close to the size needed.

Third and final question- Are there any carbon builders out there who have stock, or could source, that would sell me the appropriate tube in 1 foot lengths or so?

Thanks- RD
To q1: Not only can you refinish the tube, you have to. Since the tubes in the size you want are all "cello wrap gloss" you need to remove this surface coat to get good bonding. Simply sand with 120 grit paper USING DUST PROTECTION AT ALL TIMES until you get through the surface layer: it will be obvious when you do so, the texture of the sanded surface layer is distinctly different from that of the structural epoxy. Your surface layer should be 0.1mm or so, the cosmetic carbon layer will be about 0.2 so if you remove these two it takes the tube down to 39.8 so you'll get a 0.1mm bondline, which is good.

q2. There's a place in Australia that does custom tubes but I don't suppose that's much good to you, also I don't know what their minima are like. http://www.cstcomposites.com/

q3. Dunno.

BTW are you sure your headtube is exactly 44mm ID and not 1.75" ( = 44.45mm)? In the bike game most tube measurements are stated in metric but they're actually imperial, so if you buy a 35mm OD tube it's actually 1 3/8" = 34.925mm.

Lastly, a question for you: what adhesive and surface treatment are you planning to use? Composite bonds to steel are not easily achieved. The adhesive I use (admittedly for stainless steel, which is a bit trickier) costs me over $300 for 1.4 kg here in Oz, prices are better in the US but not that much better.

Surface treatment is another matter, I use mechanical abrasion followed by a two stage chemical etch and de-smut using nasty toxic acids which are hard to obtain in these paranoid times. I then distilled water rinse, blow dry with warm filtered air and bond immediately.
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Old 06-25-13, 09:23 PM
  #7  
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Originally Posted by Mark Kelly View Post
To q1: Not only can you refinish the tube, you have to. Since the tubes in the size you want are all "cello wrap gloss" you need to remove this surface coat to get good bonding. Simply sand with 120 grit paper USING DUST PROTECTION AT ALL TIMES until you get through the surface layer: it will be obvious when you do so, the texture of the sanded surface layer is distinctly different from that of the structural epoxy. Your surface layer should be 0.1mm or so, the cosmetic carbon layer will be about 0.2 so if you remove these two it takes the tube down to 39.8 so you'll get a 0.1mm bondline, which is good.

q2. There's a place in Australia that does custom tubes but I don't suppose that's much good to you, also I don't know what their minima are like. http://www.cstcomposites.com/

q3. Dunno.

BTW are you sure your headtube is exactly 44mm ID and not 1.75" ( = 44.45mm)? In the bike game most tube measurements are stated in metric but they're actually imperial, so if you buy a 35mm OD tube it's actually 1 3/8" = 34.925mm.

Lastly, a question for you: what adhesive and surface treatment are you planning to use? Composite bonds to steel are not easily achieved. The adhesive I use (admittedly for stainless steel, which is a bit trickier) costs me over $300 for 1.4 kg here in Oz, prices are better in the US but not that much better.

Surface treatment is another matter, I use mechanical abrasion followed by a two stage chemical etch and de-smut using nasty toxic acids which are hard to obtain in these paranoid times. I then distilled water rinse, blow dry with warm filtered air and bond immediately.
Mark- Thanks for the reply. It's encouraging and sets my mind at ease somewhat, and gives me a direction.

So, it appears since I have to remove the "surface coat" I am free to size as required.

The headtube will be reamed to 44mm (46.4 OD) to fit the headset. I figured it would be easier to ream to the finish size for the entire length, so yes- it will be 44 minus to accommodate the interference fit.

Adhesives? You mean I gots to glue it in? One builder I know of is using DP-420 to bond BB shells in CF tubes. Other than that I haven't done any research. My experience so far bonding CF to steel is CF shafts to golf club heads. In the past 15 years or so I've done hundreds (300-400 a year) but that's the extent of my experience. I'm aware of the cleanliness issues with the bond. I have never had a bonding issue. For this reason I would even consider the epoxy formulated for golf shafts.

Surface treatment? Ain't thought that far ahead. My initial thought is to provide as much "tooth" as possible. If it involves a knurl, that I can handle.

This frame is still raw tubes on the bench. Once the front is done I'll carve the headtube as I see fit and insert the CF tube. Pics will be coming.

Canaboo- I considered the method of forming CF into the relieved HT, but since the "opening" will be roughly 2/3 of the original tube I figured it was more work than I was up for, and the aesthetic I seek would not be met easily.

Thanks guys for the response. I have a path. Forward ho! Hopefully I achieve the desired result. If not the first time, we'll try again.
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Old 06-25-13, 10:09 PM
  #8  
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DP-420 is apparently excellent, I can't get it in small quantities here but I know it's what Nick Crumpton uses. The adhesive you use for the golf shafts is also probably OK. Similarly the surface prep used on the gold heads should be OK.

Don't even think about trying to form the CF into the tube, the guy who suggested this doesn't know what he's talking about.

It is notoriously difficult to mould multiple layers in a tube form which incorporates any hoop strength. The reason is one of those things that's obvious as soon as you think about it: if the first layer of fibres has appropriate hoop strength, it will be unable to move to allow compression of the next layer*. Most manufacturers of tubes get around this by mandrel winding using single tows. Really sophisticated operations can weave using muliple tows.

A second but related problem is anisotropic thermal expansion: CF composites expand a lot across the fibre lay, very little along it. If you don't plan for this in your fibre layeup, the thing can delaminate when cooling from the curing oven. This means the fibre lay must be carefully planned and take into account whether you are laminating over a female or male mould.

*If the fibres are in tension. If they are in compression, they may move but this will cause weave distortion.

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Old 06-25-13, 11:08 PM
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I know this is crazy, but I feel like that thing is mostly cosmetic so you should just slit the tube.
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Old 06-26-13, 01:11 AM
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I couldn't disagree more.

Torsional rigidity of the head tube is a major determinant of the bikes road manners. More is always better. Slitting the tube transforms the torsional stress on the tube into shear stress on the bond line. Bonding epoxies are deliberately rubberised so they can absorb these stresses by deforming, so the bond line will elastically slip.

Net result is a bike that gets squirrely in hard corners.
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Old 06-26-13, 06:42 AM
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Originally Posted by Mark Kelly View Post
DP-420 is apparently excellent, I can't get it in small quantities here but I know it's what Nick Crumpton uses. The adhesive you use for the golf shafts is also probably OK. Similarly the surface prep used on the gold heads should be OK.

Don't even think about trying to form the CF into the tube, the guy who suggested this doesn't know what he's talking about.

It is notoriously difficult to mould multiple layers in a tube form which incorporates any hoop strength. The reason is one of those things that's obvious as soon as you think about it: if the first layer of fibres has appropriate hoop strength, it will be unable to move to allow compression of the next layer*. Most manufacturers of tubes get around this by mandrel winding using single tows. Really sophisticated operations can weave using muliple tows.

A second but related problem is anisotropic thermal expansion: CF composites expand a lot across the fibre lay, very little along it. If you don't plan for this in your fibre layeup, the thing can delaminate when cooling from the curing oven. This means the fibre lay must be carefully planned and take into account whether you are laminating over a female or male mould.

*If the fibres are in tension. If they are in compression, they may move but this will cause weave distortion.
Really? Have you actually done it or are you just speculating?
Many carbon tubes are actually just laid up "loose" with the actual "hoop" not even in a continuous circle until the curing epoxy bond sets the carbon in position.
If you wrap carbon cloth around a bladder and pump it up, all the layers can slide past each other and balance out in tension.
There is a video of a Titanium bike with all sorts of holes cut in the entire frame and then lined with carbon. The carbon is rolled around the bladder and thrust into the tube and pumped up.
Perhaps you should contact them and let them know that they don't know what they are doing.
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Old 06-26-13, 08:09 AM
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Originally Posted by Canaboo View Post
There is a video of a Titanium bike with all sorts of holes cut in the entire frame and then lined with carbon. The carbon is rolled around the bladder and thrust into the tube and pumped up. Perhaps you should contact them and let them know that they don't know what they are doing.
That's the patented Exogrid technology. Several builders, including Holland, use it.

The Making of an Exogrid Bicycle (Four minute long video clip showing how the tubes are made)
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Old 06-26-13, 09:52 AM
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Originally Posted by Mark Kelly View Post
I couldn't disagree more.

Torsional rigidity of the head tube is a major determinant of the bikes road manners. More is always better. Slitting the tube transforms the torsional stress on the tube into shear stress on the bond line. Bonding epoxies are deliberately rubberised so they can absorb these stresses by deforming, so the bond line will elastically slip.

Net result is a bike that gets squirrely in hard corners.
none of this is obvious to me, seems like speculation with a potentially flawed mental model of the proposed system. Seems to me that you are saying that the carbon tube is needed to take torque, but that the bond line can't stand shear. Seems internally contradictory. It's not like anyone has ever tried having a wimpy head tube before. And I'm not sure that a well bonded slit tube would necessarily have these issues anyway. I think the carbon tube mostly takes stresses from inserting
the headset and possibly takes up some bending stresses which would be adequately addressed by a slit tube.
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Old 06-26-13, 04:54 PM
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One thing we can agree on (I think) is that the carbon tube insert, as I plan to use it is for structural purposes. I'm doing it primarily for the cosmetics, but since most of the steel tube will be cut away, it has to be sound. I'm taking the easiest of routes and going to insert a solid tube.

Unterhausen- The headset insertion will be in steel. The carbon tube won't extend entirely to the ends of the headtube. What's gonna be interesting is to see if there's any misalignment when I perform surgery on the headtube. Not sure I have enough notches in the belt to pull it off, but if I weren't confident I'd forget it.
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Old 06-26-13, 06:09 PM
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Keep in mind that if you use a solid pre-fab tube and sand off the gloss to bond it inside the steel you run the risk of removing the cosmetic external layer and ending up with carbon that looks pretty random depending on the lay-up used for the tube.
There is also the issue of galvanic corrosion. Less of an issue with steel versus aluminum but it must still be a potential problem unless the carbon/steel edge is sealed off well with the epoxy.
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Old 06-27-13, 11:04 AM
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sorry I derailed the thread, obviously a full tube would be superior structurally
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Old 06-27-13, 05:56 PM
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Originally Posted by unterhausen View Post
none of this is obvious to me, seems like speculation with a potentially flawed mental model of the proposed system.
Thinking about it some more, I agree and I resile from my position: although the torque at the head tube / down tube and head tube / top tube junctions are important, I can't see that these load the head tube itself with a significant torque.

I think the slit tube Idea is actually pretty good. IMO the best way to do it would be to do the cutout in the metal so there is a thin continuous bridge at the rear of the head tube between the aforementioned junctions. Line the tube up so the slit is bonded on this bridge: both hides the slit and reinforces the tube. It also allows you to sand away only the surface layer where the metal bits are which will look much better.
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