Stewart Palmer knew from a young age the path his career would take. As a child, he was more interested in ‘dissecting’ his bike and finding out how it worked than riding it. Now a highly skilled engineer, Mr Palmer has spent the last 18 months designing and manufacturing his own downhill mountain bike.
His engineering experience has been gained by being a programmer and machinist of components for Formula One cars and high-performance engines. However, the dream of designing his own product did not arise until he joined North Bucks Machining Ltd (NBM) (
www.northbucksmachining.co.uk), the family-owned company started by his parents in 2011 with a Haas machining centre. He and his sister soon joined the company “to take NBM to the next level”.
Mr Palmer says: “The business rapidly became successful in the three-axis machining arena, but a contract to design and manufacture eight mould tools for making five-litre Jerry Cans meant that we had to invest in technology. I previously worked at a company producing five-axis F1 parts, so my ambition was to move NBM into the five-axis market.”
This came about when the company bought a Quaser five-axis machining centre from the Engineering Technology Group (www.engtechgroup.com), along with high-end CAM software from Bicester-based Open Mind Technologies (
www.openmind-tech.com).
“High-end CAM software can be an expensive outlay for a small business with just six staff and a few Haas three-axis machining centres. My family took some convincing, but ‘the penny dropped’ when we had to produce a knife blade for a box-folding company.
"Struggling with our previous CAM system made this relatively easy re-modelling task a 2hr job. I convinced the family of the benefits of Open Mind’s HyperMill, and as soon as we bought it, I modelled the next knife tool in just 10min. They were convinced.”
As a biking enthusiast with a background in designing and producing complex parts, Mr Palmer had the idea of designing his own bike. In his spare time, he created numerous drafts of his first bike design.
He eventually took the concept to Laser Scanning, a design agency that developed a 3-D CAD model from his sketches. Once the three-piece frame design passed the simulated stress testing using finite element analysis, NBM set about machining the first bike.
Improved strength
The aim of the design was to improve the strength and structural integrity of a mountain bike. Mr Palmer says: “Standard bikes are produced from hollow tubes that are fabricated together. This design inherently has weak points on every weld seam. We elected to machine frame sections from solid aluminium billets. We calculated that we could machine our rib thicknesses down to 5mm while retaining the required strength.”
Mr Palmer’s bike 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. To emphasise the level of machining required, the main frame is machined from a 100kg aluminium billet down to a 4.5kg frame. The seat post starts as a 15kg billet and ends as a 250gm part, while the swing arm is machined from a 50kg billet and is pared down to just 2kg part.
This leaves an extremely robust aluminium frame of less than 7kg produced from an overall billet weight of 165kg. This may appear a costly and time-consuming method of production, but NBM’s aim was to prove the concept and manufacture the best possible product.
Using Open Mind’s HyperMill, the frame is machined in 40hr, the swing arm in 18hr and the seat post in 15hr. Mr Palmer says: “At this early stage, the machining time is not the key issue, it is the surface finishes. Once the frame is machined, it has no secondary hand finishing and is ready for final assembly or shipping. Its all about delivering an aesthetically perfect bike to the customer.
“That said, this project would not have been possible without HyperMill and the five-axis Quaser. Key to successful machining was the CAM system’s finish-machining cycles. HyperMill automatically groups the Z-level finishing and ‘profile-finishing’ cycles to blend perfectly between two surfaces and the two separate cycles. This is critical for our ambition of achieving the perfectly finished frame.
“Furthermore, the frame requires a lot of pocket machining, so naturally there is a radius left at the bottom of each pocket by the cutting tool. To address this, HyperMill has a ‘pencil milling’ feature that can isolate all the remaining fillets for re-machining. The machine then selects a small tool, which removes the excess material in the corner of each pocket.”
Faster machining
While surface finish is more critical than cycle times, Mr Palmer is aiming to reduce the machining time by implementing Open Mind’s new HyperMill Maxx machining package for rough machining. NBM has run tests with this new software and found the cycle time reduction to be extremely positive. For example, one of the roughing cycles on the main frame has been reduced from 2hr 20min to less than 1hr 30min.
Mr Palmer estimates that if that part was run on a machine with a spindle speed in the region of 15-18,000rev/min, as opposed to the existing 8,000rev/min, the cycle time would fall close to 30min — a massive 80% reduction on the existing run time.
Although the project is in its infancy, Mr Palmer aims to further enhance the design of the frame to reduce the overall weight from 6.75kg to approximately 5kg. As an engineer with a background in F1 design and production, getting the frame to shed a few grams as it progresses will be second nature.
NBM, which is based in Milton Keynes, is looking to retail the three-part frame and rear suspension unit for about £7,000 — or a completely built bike with top-specification equipment for about £10,000. Open Mind Technologies will have a complete bike on its stand at MACH 2016.