A welcome early visitor to the Engineering Technology Group (ETG) stand at the MACH exhibition was Sir Chris Hoy MBE the former track cyclist and six times Olympic gold medallist.
After he had officially opened the Show he took time out to visit a few of the stands including ETG where an example of a finish machined innovative cycle frame caught his eye. The frame was machined on an ETG supplied Quaser 5 axis machining centre by North Bucks Machining Ltd (NBM). A frame was being machined on a Quaser VMC as part of a demonstration on the ETG stand.
CNC machined bike frames are still fairly rare and this particular downhill bike example is the brain child of NBM director Stewart Palmer, a fifth generation engineer with past experience of machining F1 race car components and high performance engine parts.
Stewart’s parents founded North Bucks Machining in 2011 and he joined the fledgling business soon after with the aim of taking the company out of conventional 3 axis machining into the era of 5-axis, in which he was particularly adept.
Machining skills aside Stewart also enjoys cycling in his spare time, and with the dream of creating his own project suddenly possible he spent 18 months designing and building his first bike frame.
NBM invested in a Quaser MF630U after Stewart’s previous experience with Bridgeport CNC’s brought them to Southam based ETG who identified the Quaser VMC as the most suitable machine for their overall needs.
“ETG took onboard our machining environment while being aware of our long term aims so we opted for a machine that gives us ample scope,” explains Stewart. “The five axis aside – and the contouring capability in particular - it has a really good table size of ø500 and we opted for a 48 BT40 tool capacity ATC mindful of the complexity of many of our projects – particularly moulds and tools – which require multiple tooling set up’s.
“We also specified Blum touch probing and a Heidenhain control as this was the one I was most familiar with.”
The MF630 is a fully simultaneous 5 axis VMC with rapid movement across its X, Y, Z axes of 32/32/16 m/min respectively. As standard it is equipped with a coolant chiller and through coolant capability and features positional accuracy of 0.008/0.004 and a 12,000rpm NC40 coupling spindle.
The company now uses the Quasar in conjunction with Open Mind’s HyperMILL cam software, an upgrade that made the bike project possible.
Working from Stewart’s sketches of the frame a 3-D model was created, then virtually simulated loads and stresses on the design undertaken before the machine work began.
After completing the stress tests the aim of the design was to improve the strength and structural integrity of a mountain bike. To eliminate weak points and weight, NBM used solid aluminium billets and i-beam technology to scallop out the sides of the frame to reduce mass. They calculated they could machine rib thicknesses down to 5mm on the Quaser whilst retaining structural integrity but there was still a high level of machining and skill required.
The design consists of three core features, the main frame, the seat post and the swing arm that connects the main frame to the rear wheel and suspension with the all aluminium frame weighing less than 7kg from an overall billet weight of 165kg.
This may appear a costly and time consuming method of production, but NBM investigated waterjet cutting and the time and cost element was similar. The aim was to prove the concept and manufacture the best possible product.
The project is still in its infancy but Stewart has ambitions to further enhance the design of the frame to reduce the overall weight from 6.75kg to approximately 5kg, well within the capabilities of the Quaser machine.
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