Although The Racer is a track/TT bike concept, the focus has not been on function and performance. Instead, we set out to explore the possibilities of cost effectively manufacturing one-off frames based on unique designs.
Stage V of The Racer involved a significant change in the manufacturing method. There were too many surface quality problems using a single positive mould (i.e. laminating directly on a foam model). Instead, two negative moulds were CNC machined from modelling board. Two half-shells were laminated using weaved carbon fibre fabric and an experimental carbon nanotube modified epoxy resin system with finely dispersed CNTs, which form a strong bond with the matrix. The half-shells were joined with an adhesive to form the main frame. Due to limitations both in the machining area and available monolithic modelling board, only the front part of the frame was made this way. An off-the-shelf rear triangle set was used to complete the frame. The frame weighs 1,8 kg.
Acknowledgements: The project was mostly funded by TTER, parts were provided by Cycleurope and the adhesive, surface prep materials and vinyls are from 3M. Some carbon tubing was provided by Kevra.
Stage IV is an intermediate step between the previous foam cored full monocoque designs and the planned main frame from two half-shells with tubular rear fork. The main frame was made as previously, but the rear fork and integrated seat tube were cut from an aluminium mountain bike frame.
Stage III is based on the previous version, but the shaping of the foam core was made using CNC hot wire. This allowed us to make the core more accurately and from fewer parts. Shearing of the foam under mechanical loading has been the weakest link of the sandwich structure, but the hot wire cutting melts the surface of the foam and increases its the density where the shear strength is needed most. This way we achieve a variable density foam core simultaneously with shaping of the foam. A super light 88 mm wide bottom bracket shell was bonded to the frame. The bearings are pressed directly to the BB shell without any cups, much like the BB30 standard, but our solution allows the use of cheaper “external bearing” cranksets. The frame weighs 2,0 kg.
Acknowledgements: Polystyrene foam was offered by Finnfoam, the CNC hot wire cutting by Naccanil and vinyl by 3M Finland.
Stage II of the racer was manufactured based on a 3D CAD model. The silhoutte of the front part of the frame and the rear fork were printed in 1:1 scale and used as a template for cutting an XPS foam slab. The foam was shaped with a band saw machine and the chamfers with a knife and ruler. The fork ends and headtube were glued to the foam core before laminating. The frame was mostly laminated in one step. The seat shell was laminated to the frame afterwards and the aluminium BB shell bonded.
Stage I of the racer was made to acquire better understanding of the manufacturing process and the design limitations it poses. No proper design work or drawings were made for this one, just a quick and dirty prototype in order to learn from mistakes. The rear fork ends were cut directly into the sandwich structure, but they worked poorly because the core material got crushed when tightening the rear axle.