A mountain (bike) of chips

END USER: North Bucks Machining Ltd., +1908-611-669, www.northbucksmachining.co.uk
SOLUTION PROVIDER: Open Mind Technologies USA Inc., (888) 516-1232, www.openmind-tech.com
CHALLENGE: Efficiently rough-machine a mountain bike frame from a solid piece of aluminum stock.
SOLUTION: A CAM software’s high-performance roughing module.

Machining a bicycle frame from solid stock instead of welding hollow tubes together enhances the frame’s strength and structural integrity. This is because the frame doesn’t have the weaknesses that welding or otherwise joining two or more pieces can create. That’s according to Stewart Palmer, engineer at North Bucks Machining Ltd., a five-employee parts subcontractor started in 2011 by his parents, Dave and Rose.

And he should know, because, to date, Milton Keynes, U.K.-based NBM has machined two 4.5kg (9.92 lb.) prototype bike frames from a 100kg (220.5 lb.) 608 aluminum billet in connection with a mountain bike Palmer designed and built. “We used solid aluminum billets and I-beam technology to scallop out the sides of the frame to reduce mass,” Palmer said, noting the aim was to prove the concept and make the best possible product. “We calculated that we could machine our rib thicknesses down to 5mm while retaining structural integrity.”

In addition to the frame, the bike design consists of two other core features: the seat post and the swing arm that connects the frame to the rear wheel and suspension. The seat post starts as a 15kg (33.1 lb.) billet and ends as a 250g (0.6 lb.) part, and the swing arm is machined from a 50kg (110.2 lb.) billet down to a 2kg (4.4 lb.) part.

North Bucks Machining machines an aluminum swing arm for a mountain bike (inset)
in a Quaser MF630 U-type 5-axis vertical mill. Image courtesy of North Bucks Machining

Although NBM has a Quaser MF630 U-type 5-axis vertical mill, which has a maximum swing of 630mm (24.8″), Palmer explained that the frame is too large to machine in that machine, so the company used a Haas 3-axis machine, which required 10 to 12 setups. “If it could have been manufactured on the 5-axis, we would have greatly reduced that number,” he said.

Palmer added that NBM uses hyperMILL CAM software from Wessling, Germany-headquartered Open Mind AG (Open Mind Technologies USA Inc. is located in Needham, Mass.) to make more efficient use of its machine tools. During a trial to produce the second frame, NBM incorporated the roughing module in the hyperMILL MAXX Machining performance package. “When we switched to the hyperMILL MAXX Machining strategies, the engineering technology group at Quaser lent us a 3-axis machine to do the test on,” he said, adding that the initial switch was done in connection with a live cutting demonstration at a trade show where the Quaser machine was allocated to NBM. “All we did was change the cycles and change the way we look at roughing.”

According to the software developer, the roughing module creates spiral and trochoidal toolpaths that significantly increase material-removal rates. This reportedly enabled extremely fast machining while reducing stress on the cutting tools and machine.