I have been cycling on a recumbent bike for 2 years now and it is time to move to a lighter and stiffer bike.
A carbone High Racer as we called them is a recumbent with 2 x 26' wheels. They are not as fast as Low racers (20' x 26') but they are good for training. They are also higher than low racers and you can ride more easily with normal up-right bicyles.
1-The first stage is to design the bike frame on CAD with a 2D software such as Autocad. The shape is up to you but you must bear in mind that the chain line must avoid the frame and the brakes.
If you don't have any knowledge about structure then avoid small x-sections because carbon can't always make miracles.
Basic dimensions: (main section 96mm x 65mm) . After the first ride, I noticed that the chain was too close to the rear break and a pair of lug were required. The seat is now a bit higher than shown on the drawing.
2-Once you are happy with your drawing, transfer the file on a USB key and bring it to your local printer. (print cost about 8euros)
3-Then buy extruded polystyrene sheets ( 2 x 1250 x 600 x 20mm thick-blue styrodur is best but pink is acceptable, avoid yellow foam) in a DIY shop.
4-Bond sheets together with propiatory glue (make a test first!).
5-Then use 3M spray adhesive (for pictures) and glue paper drawing (precisely cut with scissors) on the foam.
6-Use a hot wire to cut the foam. Avoid saw where possible as it gets messy in the garage.
Split rear fork through thickness.
7- Rebond rear fork in a curved shape. (use a template to fit hub width of 135mm)
8- Drill bottom braket hole (34mm) and steering column (34mm)
9- Cut foam to desired X-section. Use a small 'Sur-form' and sand paper (80 and 400 grit)
10- Build a template frame to maintain frame with perfect angle during lamination ( foam is not very stable with heat variation); you can prepare every template on CAD and buy precisely cut MDF.
11- Prepare single skin rear luggs , 5mm thick max.
12- Fit foam core on template frame and bond premade rear luggs.
13- Laminate the steering column pole with 2 x carbon +/-45-300g/m² and epoxy resin about 80mm longer than pole. Slide the foam core over the pole ( tape the top end of the pole to hold carbon while slinding done the core) and fold the extra carbon length (40mm each side) on the outside of the foam. Reapeat this operation for the bottom bracket. Finish with a layer of peel ply which will level the overlap bump. Let it cure.
14- Check foam core for any unwanted renin drops.
15- Prepare carefully the carbon layers to cover the bottom part of the frame. Basic specification in my case: 1 carbon UD300 at 0°,1 carbon UD250 at +45°,1 carbon UD250 at -45°, 1 carbon twill 300 at 0/90°.
16- Wet out foam core where you expect to place the carbone and add 20mm alround.
17- Laminate carbone with long working time epoxy resin (8H should be Ok) on a plastic film. Pour some resin on the plastic film then drop the carbon on to it. Use a squeeze to force the resin throught the carbone. Apply more resine if require. Use the squeeze to remove excess resin.
18- Place carbon layers one by one the the foam core. It is important to remove every air pocket trapped under the carbon. A second personn is very helpful at this stage.
19- Finish with a layer of peel ply and use your hand (always use latex or rubber gloves with epoxy) to squeeze the carbone and remove any air bubble.
20- Let it cure at room temperature. I recommand to laminate when temperature starts to go down in the afternoon because air pockets can kick in if temperature rises. Avoid direct sun light.
21- remove peel ply and use a grinder to smooth carbon/foam transition.
21- Laminate second half of frame.
At this stage, the frame weighs 1900g (this includes the boom)
22- fill and fair.
23- Check assembly before painting.
24- Modification: After 200Km of testing, it is time to make a couple of improvement before painting. The major problem was the chain ragging against the rear break so the rear wheel support has modified. New single skin plates were bonded and laminated. The clearance is now 20mm between the chain and the break when riding on the big ring.
I made a carbon tiller over the WE. I used and aluminium stem, a bit of polystyrene and 1 layer of carbon cloth 300g/m².
this is the tiller before laminating. the aluminim bit is on the left hand side and on the right handside, you can see 2 single skin E-glass plates (4mm). The tiller and tilt up and down.
24- Paint with 2 pack paint (car paint) and finish with a varnish.
