I have been recently e mailed quite a few questions about carbon fibre, such as how to do cosmetic, as well as structural repairs. Well, I feel that I need to put out what I know (which is little in the comparison to the likes of Steve Hed, and the folks at Nimble) so some questions can be answered.
What is OCLV?
It is not a trademarked name (that I know of), it is an actual certification through testing. Optimum Compaction Low Void is what OCLV stands for.
Optimum compaction is how much fibre content is to how much epoxy. 35% epoxy is as low as I have heard anyone responsibly report it. Most wet layups yield anywhere from 70/30 (epoxy to fibre) to 40/60 (which is phenomenal!), depending on methods used to extract epoxy.
Low void is just what it says- minimal air bubbles. Air bubbles typically occur in a wet layup due to whipping air into the epoxy mixture, or not making sure that the fabric does not wrinkle or pucker in the layup. I typically test how well my void factor by laying up a small item, vacuum bag it, then saw it in half.
Air bubbles can cause the "pin prick" appearance in a cosmetic layer of a composite item. These will not reflect on the quality of the item, and it is best to leave the pin pricks alone. It is part of the unique, not all are exactly the same nature of carbon fibre.
Is all carbon fibre woven?
Yes and no. I am actually building an item from high-modulus woven fabric, as I get many, many different fibre orientations in my layup. Many companies use uni-direction graphite in their layups (0 deg., 60 deg. in two directions, and 90 deg. angles), and some use filament winding, which is generally the very most expensive way to make carbon tubes. You will know it if something is filament-wound, as it was a very expensive process for one to master. Filament wound tubes generally have a ubiquitous look (look at a Wound Up fork for the best example).
What is better, a composite item with a core or hollow?
Hollow objects need to have more layers of cloth to make up for the lack of stiffness that a core provides. A handlebar can use up to 18 layers of pre-preg, as it relies on more material to make sure that the item does not bend. Hollow items can be bladder moulded, rendering a true one-piece item; some are vacuum formed in halves and glued together. No method is superior.
An item with a core, whether it be foam, nomex, or balsa wood, needs less layers of fabric, as the carbon is stiffened by the core. A Renn or a Zipp disc is actually quite soft on the outside, but the nomex honeycomb core makes it super stiff. A hollow disc would be tougher on the outside, but needs considerably more material to make it stiff.
Tube and lug carbon frames will have plenty of material, especially when the carbon tube is fused with a carbon lug. The best carbon frames are made like this, like the Trek OCLV, Calfee, Parlee, Colnago C40/50, etc.
What do I think? Monocoque frames are best when they have a core (my Corima Fox weighs about two and a half pounds), and tube and lug frames will be your lightest carbon frames. One qualifier here: the Cat Cheetah is probably one of the very best hollow frames, as it is autoclaved to an OCLV standard.
Can I repair carbon fibre myself?
Yes, with electrical tape, carbon tapes (by West Systems), West Systems Epoxy, sand paper, acetone, and some time and patience. It won't look nearly as pretty as it came from the factory, but will be stronger. E mail me if you want pointers.
What is OCLV?
It is not a trademarked name (that I know of), it is an actual certification through testing. Optimum Compaction Low Void is what OCLV stands for.
Optimum compaction is how much fibre content is to how much epoxy. 35% epoxy is as low as I have heard anyone responsibly report it. Most wet layups yield anywhere from 70/30 (epoxy to fibre) to 40/60 (which is phenomenal!), depending on methods used to extract epoxy.
Low void is just what it says- minimal air bubbles. Air bubbles typically occur in a wet layup due to whipping air into the epoxy mixture, or not making sure that the fabric does not wrinkle or pucker in the layup. I typically test how well my void factor by laying up a small item, vacuum bag it, then saw it in half.
Air bubbles can cause the "pin prick" appearance in a cosmetic layer of a composite item. These will not reflect on the quality of the item, and it is best to leave the pin pricks alone. It is part of the unique, not all are exactly the same nature of carbon fibre.
Is all carbon fibre woven?
Yes and no. I am actually building an item from high-modulus woven fabric, as I get many, many different fibre orientations in my layup. Many companies use uni-direction graphite in their layups (0 deg., 60 deg. in two directions, and 90 deg. angles), and some use filament winding, which is generally the very most expensive way to make carbon tubes. You will know it if something is filament-wound, as it was a very expensive process for one to master. Filament wound tubes generally have a ubiquitous look (look at a Wound Up fork for the best example).
What is better, a composite item with a core or hollow?
Hollow objects need to have more layers of cloth to make up for the lack of stiffness that a core provides. A handlebar can use up to 18 layers of pre-preg, as it relies on more material to make sure that the item does not bend. Hollow items can be bladder moulded, rendering a true one-piece item; some are vacuum formed in halves and glued together. No method is superior.
An item with a core, whether it be foam, nomex, or balsa wood, needs less layers of fabric, as the carbon is stiffened by the core. A Renn or a Zipp disc is actually quite soft on the outside, but the nomex honeycomb core makes it super stiff. A hollow disc would be tougher on the outside, but needs considerably more material to make it stiff.
Tube and lug carbon frames will have plenty of material, especially when the carbon tube is fused with a carbon lug. The best carbon frames are made like this, like the Trek OCLV, Calfee, Parlee, Colnago C40/50, etc.
What do I think? Monocoque frames are best when they have a core (my Corima Fox weighs about two and a half pounds), and tube and lug frames will be your lightest carbon frames. One qualifier here: the Cat Cheetah is probably one of the very best hollow frames, as it is autoclaved to an OCLV standard.
Can I repair carbon fibre myself?
Yes, with electrical tape, carbon tapes (by West Systems), West Systems Epoxy, sand paper, acetone, and some time and patience. It won't look nearly as pretty as it came from the factory, but will be stronger. E mail me if you want pointers.