Trying to get my carbon fork from 43 to 45 mm rake -- correct heating temperature?
01-15-15, 01:22 PM
#101
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01-15-15, 01:44 PM
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Epoxy has a glass transition temperature, at which point it becomes flexible. However, the carbon fiber in the mix does not have a glass transition temperature and can be damaged, as it would need to slip in the epoxy and that epoxy may not be that flexible.
Most epoxy reaches the maximum service temperature where it starts to degrade before the glass transition temperature, by design as it is supposed to be rigid.
Without verifying any of the epoxy characteristics, you must assume what you now have a dangerous weak and useless fork. Please destroy it so it does not get out there on ebay. Sorry, thermosets do not behave like thermoplastics.
Rod
Most epoxy reaches the maximum service temperature where it starts to degrade before the glass transition temperature, by design as it is supposed to be rigid.
Without verifying any of the epoxy characteristics, you must assume what you now have a dangerous weak and useless fork. Please destroy it so it does not get out there on ebay. Sorry, thermosets do not behave like thermoplastics.
Rod
Likewise, the epoxy on the forks was cooked at the factory. It may be safe if one doesn't exceed the temperatures used during fabrication.
One of the problems is that many home tools would give a direct heat source... you need to uniformly heat the whole fork (at least the legs, I'd be careful about the crown and steer tube). So you'd likely be better off with an oven which you can precisely control the temperature vs a hand held heating device.
The point of the carbon fiber cloth (rather than just using plastic) is to give a rigid structure. Bending it may defeat this somewhat, but perhaps a very gentle bend won't significantly affect it, and many fiber cloths have a flexible weave which makes them easier to work with, so a percent or two bend over the length of the fork may be fine.
Anyway, it sounds ike the OP is doing the experiment. I'd take it easy, and just see what it feels like before hammering any hard corners or riding in tight draft lines.
01-15-15, 02:31 PM
#103
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Carbon, Graphite, and various fibers have a very high melting point. You're unlikely to damage them with a little heat.
Likewise, the epoxy on the forks was cooked at the factory. It may be safe if one doesn't exceed the temperatures used during fabrication.
One of the problems is that many home tools would give a direct heat source... you need to uniformly heat the whole fork (at least the legs, I'd be careful about the crown and steer tube). So you'd likely be better off with an oven which you can precisely control the temperature vs a hand held heating device.
The point of the carbon fiber cloth (rather than just using plastic) is to give a rigid structure. Bending it may defeat this somewhat, but perhaps a very gentle bend won't significantly affect it, and many fiber cloths have a flexible weave which makes them easier to work with, so a percent or two bend over the length of the fork may be fine.
Anyway, it sounds ike the OP is doing the experiment. I'd take it easy, and just see what it feels like before hammering any hard corners or riding in tight draft lines.
Likewise, the epoxy on the forks was cooked at the factory. It may be safe if one doesn't exceed the temperatures used during fabrication.
One of the problems is that many home tools would give a direct heat source... you need to uniformly heat the whole fork (at least the legs, I'd be careful about the crown and steer tube). So you'd likely be better off with an oven which you can precisely control the temperature vs a hand held heating device.
The point of the carbon fiber cloth (rather than just using plastic) is to give a rigid structure. Bending it may defeat this somewhat, but perhaps a very gentle bend won't significantly affect it, and many fiber cloths have a flexible weave which makes them easier to work with, so a percent or two bend over the length of the fork may be fine.
Anyway, it sounds ike the OP is doing the experiment. I'd take it easy, and just see what it feels like before hammering any hard corners or riding in tight draft lines.
From Columbus:
Carbon forks can be long lasting but one has to take care of other aspects than metal ones.
A fiber composite material has higher mechanical characteristics than metals (higher tensile strength, higher fatigue life, higher stiffness) but it has even different behavior due to its “non-homogeneous nature”. This means that the fork project is really a “critical point” for life span, moreover the final user has to check the composite fork with attention to different aspects compared to metal one. In fact, for composite material the areas of coupling with other parts are critical (headset bearings, stem clamp, gap cap),composite has different impact behavior so for each shock is important to check fork, finally composite is sensitive to ambient agents (solvents, temperature over 90°C etc).
–Riccardo Carpinacci
R&D department, Columbus, Cinelli and 3T
Carbon forks can be long lasting but one has to take care of other aspects than metal ones.
A fiber composite material has higher mechanical characteristics than metals (higher tensile strength, higher fatigue life, higher stiffness) but it has even different behavior due to its “non-homogeneous nature”. This means that the fork project is really a “critical point” for life span, moreover the final user has to check the composite fork with attention to different aspects compared to metal one. In fact, for composite material the areas of coupling with other parts are critical (headset bearings, stem clamp, gap cap),composite has different impact behavior so for each shock is important to check fork, finally composite is sensitive to ambient agents (solvents, temperature over 90°C etc).
–Riccardo Carpinacci
R&D department, Columbus, Cinelli and 3T
Read more at Technical FAQ with Lennard Zinn: Carbon Forks - VeloNews.com
...the internet, where dubious advice is free, and you get what you pay for.
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01-15-15, 04:44 PM
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OP, BF needs threads is this You are a member with vision. Necessity is the mother of invention, and your invention of the 45 mm rake fork will revolutionize the cycling world. I feel stupid for simply buying a $100 one from Nashbar.
01-15-15, 06:15 PM
#108
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Red Green would be proud of you, but you need more duct tape.
01-15-15, 06:44 PM
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Oh, come on. Madison, Wisconsin, home of U of W. This has to be a wind up. Look at that picture. This guy says he's a perfectionist. I mean, can you stage a picture more likely to egg on BF members?
01-15-15, 07:36 PM
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You have it backwards. Thermoset is polymer that cross links irreversibly with heat. Thermoplastic is is a polymer that doesn't crosslink with heat and can be reformed. Thermosets are plastics like epoxy, phenol/formaldehyde, urethane, and polyesters for example. Examples of thermoplastics are PET, polypropylene, polyethylene and nylon.
You are correct that the fork shouldn't be reformed.
You are correct that the fork shouldn't be reformed.
Last edited by rpenmanparker; 01-15-15 at 07:48 PM.
01-15-15, 09:29 PM
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...I want to try this, but in order to be safe, I'm gonna heat my fork in the crock pot.
...I want to try this, but in order to be safe, I'm gonna heat my fork in the crock pot.
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01-15-15, 09:47 PM
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I'm a bit surprised this has gone on so long.
I'm thinking I might list a noted bridge over in the marketplace forum.
I'm thinking I might list a noted bridge over in the marketplace forum.
01-15-15, 10:28 PM
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I notice your a fellow Madison resident. Perhaps you heard of this story from a few months back: Bicyclist in critical condition after crash possibly caused by broken fork, police say : Madisondotcom
That crash was at low speed in an intersection. As far as I have heard, he has not woken up yet.
That carbon wrap is a joke - a haphazard wrap like that slathered with a bit of epoxy will add very little strength, and you'll never get a good bond to the already-cured fork. I'll keep an eye on the obituaries for you.
That crash was at low speed in an intersection. As far as I have heard, he has not woken up yet.
That carbon wrap is a joke - a haphazard wrap like that slathered with a bit of epoxy will add very little strength, and you'll never get a good bond to the already-cured fork. I'll keep an eye on the obituaries for you.
01-15-15, 10:35 PM
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Oh my god I think I recognize some of the tools in that shop. Please, please tell me this is all a big joke and no one at Freewheel/Bike Right/whatever its called these days is stupid enough to let you do this there.
01-15-15, 11:20 PM
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At least BF is a free site. If he does ride that fork and something drastic happens to him he's not out his cost of a years membership.
01-16-15, 11:16 AM
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My suggestion for the OP, please acquire a Go-pro if you don't have one and attach it to your helmet, if you wear one and record all future rides on this fork.
I can't wait to see the footage.
I can't wait to see the footage.
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01-16-15, 12:02 PM
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They are probably sitting around giggling after pranking BikeForums.
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01-16-15, 04:11 PM
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Polyesters can be either thermoset or thermoplastic depending on the chemical structure. PET is a specific polyester that is a thermoplastic. Unsaturated polyesters, such as those used in fiberglass, are usually thermosets.
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01-16-15, 05:07 PM
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01-16-15, 07:29 PM
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For this very small amount of rake, if you really HAD to change it, I would have just filed the drops a bit wider and pushed the wheel to the front when tightening the quick release. Would have been done in less than an hour and no cosmetic issues to deal with.
01-16-15, 09:33 PM
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First I was using a propane torch, running it up and down while I had the fork ends clamped against a spare hub and quick release in a vise, then I'd push and see if it would budge. It hasn't worked great, and there's been a little bubbling and singeing. So I switched to a paint stripping hot *** and put a really long pipe over the steer tube to get more leverage after things get hot. It seemed to bend a bit. I think I am sitting on at least a 44 rake, but one of the legs has deformed a bit.