Monday, April 23, 2007

Carbon Low racer

First test of the bike today.
After bonding the seat,I realised that the bottom bracket was 20mm too far so I had to trim the frame!
The first test is always scarry because something can break but nothing did.
The forward part of the frame is not stiff enough so I need to reinfrce it. The global stiffness seems to be acceptable.
I can fit a front break at the moment so I need to find a solution soon at it is not acceptable to ride on a road with a single rear break.
The fork has not the correct angle but it is too late to change.
The final weight of the complete bike is 7.8Kg. My target was less than 7Kg so need to up-grate a few things like the handle bar, the foam pad and the rear wheel (1.8Kg!).

Carbon Fork.
I already built a carbon fork two years ago for my Baron X-low because the chain was touching the fork. So I built an asymetric fork similar to the VK. I start from a foam former. I laminated a couple of layers of carbon (UD and +/-45) to form an arch. Then I used a PVC pipe as a former for the steering tube. I laminated more carbon and vacuumed bag the whole lot. As expected the sttering tube was far from perfect so some carbon had to be ground off. The final weight was about 290g and the stiffness was just acceptable sideways.

From that first experience, UI decided to use a female mould for the steering tube. I wanted to use a badder to build the tube but at the last minute I decided to use a piece of round foam that would be soft enough to squizz when the female mould would be closed.
Arch laminate over full width:
1 x CAUD300-620mm long ( carbon unidirectional)
1 x CADB400-620mm long (carbon double bias +/-45 stitch fabric)
2 x CAUD300-620mm long
4 x CAUD300-270/230/200/100mm long
2 x CACL300-220/200mm long (carbon cloth 0/90-weaved fabric)
1 x CADB300-620mm long

Steering tube:
1 x CADB400-190mm long (carbon sock +/-45)
2 x CAUD300-33mm wide-500mm long
2 x CAUD300-33mm wide-275/200mm long
8 x CAUD300-25mm wide-225mm long
1 x CADB400-225mm long (carbon sock +/-45)

On the picure below, you can see the arch built on a boam former, a small piece of PVC foam (AIREX C70.75) bonded a the top to take the local shear load and align the female mould, the'soft' foam round piece and the precut carbon. The carbon is laminated on a table and the excess of resin is removed with a squeegy.

Each layer is then applied on the fork and they are 'hand pressed' to remove any bubble

This is a carbon sock (+/-45). This a wonderful product as it fits almost every diameter and you don't have to worry or struggle with the +/-45 distorting too much.
It is also possible to buy unidirectional sock.

The female mould then clamps the steering tube. I advise that use use a sacrificial layer as the last layer might be trapped at the join. Many bolts and a stiff mould are required to garanty a good clamping pressure. I then fitted everything in a high elongation vacuum bag from AEROVAC (400% elongation)because I had a sample. I left the foam former in the arch because it had a centre line and it has be used to align the steering tube. I cooked every thing at 40degC during 2H30. This garanties that the resin is totally fluid and will impregnate the carbon totally.
Final weight of the fork is 260g but more trimming can be done.


After 40min of foam shaping, I was ready to laminate the underside with a layer of carbon/Kevlar. (that is the only material I had in my garage at that time.) The upper and lower skins overlap over 15mm alround the seat. I also added 3 transverse carbon UD reinforcement 30mm wide in way of the expected support points.
Final weight is 470g.


I used a sheet of polystyrene 100mm thick to make my seat. Two MDF profiles were used with a hot wire to get the correct curve. The foam is wide enough to make 2 seats. For my next seat, I will use a heavier density foam because it will be easier to sand. The inside surface has been then covered by a layer of carbon cloth 300g/m2 (weaved 0/90)

14-02-08 Back on track.

The bottom bracket in bonded in the frame with filled epoxy. I wrapped a couple of carbon fibres arround the outside to build up the local thickness. I need to make a nice fillet and vacuum bag a couple of tapes (+/-45deg).

The carbon bottom bracket is built on a tube wrapped in a teflon adhesive film. The thread is an Italian/english adaptator thread. I applied 2 layers of carbon (carbon cloth 300g + carbon UD at 90deg and a couple of fibres diretely on the thread) and demoulding the bottom brackets comes to just 15g instead of 50g for its aluminium counterpart.
04 May 2007: The frame has been sanded and is ready to received a layer of vanish.

Wheels are fitted but the crank is still missing.

Le cadre a été poncé et est prêt à recevoir une couche de vernis.

Les roues sont montées mais le pédalier manque toujours.

The front wheel is not as close to the frame as expected due to head set bearing (1'' is higher than integrated 1''1/8)
The shimano back wheel is a bit heavy but it should be very streamlined. Testing will tell.

La roue avant n'est pas aussi proche du cadre qu'espéré à cause de la direction head set (1'' est plus haut que 1''1/8 intégré)
La roue arrière shimano est un peu lourde mais devrait être très profilée. Les essais le diront.

The peel ply layer and the mesh used during the vacuum process are partially removed.

Le tissus d'arrachage et le fillet utilisé lors de la construction sous vide sont partiellement retirés.

15 April 2007:
I have just started a new carbon Low racer frame.
Je viens juste de commencer un nouveau cadre de Low racer en carbone

The crank is placed as low as possible to maintain a good blood pressure in my legs. I also feel that it is important to cool the front the legs.
Le pédalier est placé aussi bas que possible pour maintenir une bonne pression sanguine. Il me semble aussi important de refroidir le devant des jambes.

The chain is as straight as possible. The bike will be fitted with Corima wheels.

The core is made of extruded polystyrene (Yellow) 50mm thick.
The entire frame is covered with a layer of carbon double bias(+/-45) 300g/m2 + a layer of carbon cloth (0/90) 300g/m2. I have added a couple of local reinforcement (unidirectional) to stiffen the frame ( a drawing will be added later)
Foam core: 238g
Aft fork covered: 350g
1/2 side covered: 700g
Expected final weight: 1200g

La chaine est aussi droite que possible. Le vélo sera équipé de roues Corima.
Le noyau est constitué de polystyrère extrudé (Jaune) de 50mm d'épaisseur.
Le cadre est entièrement recouvert d'une couche de bi-biais (+/-45deg) 300g/m2 et d'une couche de carbone sergé (0/90) 300g/m2. J'ai ajouté quelques renforts locaux ( unidirectionel) pour rigidifier le cadre. ( un dessin sera ajouté plus tard)
Noyau mousse: 238g
Fourche arrière couverte: 350g
1/2 coté couvert: 700g
Masse finale probable: 1200g.