Software developer Russell Kappius had an idea for a new bike hub/design, but he needed metal laser-sintering manufacturing technology to handle the design complexity.
About four years ago, Russell Kappius, a mountain-bike enthusiast and winner of six Masters racing titles, and a research geophysicist/software developer, became obsessed with bicycle hubs. He wanted more speed and responsiveness, but wasn’t sure how to get it.
His ‘Aha!’ moment came when a demo part from one of the bicycle industry’s major suppliers arrived in the mail. “When I saw it, I got an idea for a new hub-drive system,” he said. “I did a patent search and quickly learned that there wasn’t anything out there that covered what I was thinking.”
After working out a design for a novel oversized hub and high-performance drive assembly that would transfer more power from pedal to chain to wheel, Kappius patented the concept and began looking for a way to fabricate the parts.
The manufacturing conundrum
Kappius first knocked on the door of a fabricator who offered water-jet cutting. But the process was limited in its capacity to produce dimensionally accurate and complex parts. Next, he tried wire electrical discharge machining. This method produced parts that met specifications, but it had a fairly long turnaround time and could only fabricate 2.5D geometries, a constraint to component shape. With no better option available at the time, however, he settled on this technique.
For two years, Kappius and his son, Brady (an engineer and pro mountain-bike rider), field-tested versions of their hub and tweaked its design. “Because we’re a startup, we quickly learned that we needed to make design changes and get new parts out to our customers fast,” the elder Kappius said. “We had to leverage our time to market to stay competitive.”
Then in late 2011, Kappius discovered direct metal laser sintering (DMLST), an additive manufacturing technology that met their rapid turnaround needs and enabled them to produce parts to exacting specifications and with additional design complexity. He also found Harbec, an Ontario, New York-based DMLS provider, and sent them a CAD file that included the latest round of design refinements.
About thirty days later, the father-son team received new parts. And in the first week of field testing, the elder Kappius won a race using the latest hub assembly. “We went from concept to bike-ready components in about a month,” he said. “I’ve never been able to move that quickly before.”
Laser sintering sharpens the competitive edge
Kappius Components’ hubs have been through a half-dozen design iterations since he opened for business in 2008. But the recent move to laser sintering accelerated the speed of improvements. “As a software engineer, I am able to change anything at any time to make the code better,” he said. “With DMLS, I have similar flexibility. It allows me to make small design changes and almost immediately test them on the bike. That’s the beauty of the technology.”
The lightweight-yet-durable hub, on the other hand, comes from the sleek carbon-fiber shell (handmade by the younger Kappius), as well as the drive assembly housed inside it. The assembly is comprised of three major parts: an outer drive ring, an inner ring with 60 teeth, and eight pawls (or flippers), which engage in pairs with the teeth on the inner ring. This setup functions like a ratchet (as in other drive trains) allowing forward motion while preventing backward motion.
The technological advance in the system comes from two developments: the oversized design, it’s about twice the current standard diameter, and many more points of engagement than standard designs. These two features constitute the heart of the hub’s intellectual property and allow a cyclist to translate the act of pedaling into increased drive force.
When he first geared up for business, Kappius bought ready-made pawls and engineered the rest of his system around them. Once he discovered laser sintering, however, he was able to redesign the pawl itself and add a one-millimeter cylindrical basal extension, which positioned them better when they engaged.
One advantage of laser sintering is the ease with which it can manufacture cylindrical and other irregularly shaped parts, like Kappius’ pawls. Since it’s an additive rather than subtractive process, the technology “grows” parts layer by layer using powdered materials (metals, polymers, and foundry sands) that are heated and melted by a laser. The beam follows the outlines and contours of a series of cross-sectional slices taken from a 3D digital model.
“There is no way we could have improved our pawl design using wire EDM because that method cuts parts out of flat pieces of metal,” said Kappius. “DMLS has freed us to make improvements on all of the elements in the system.” The technology has also helped level the playing field between Kappius’ two-person company and the bigger players in the bicycle industry.
Small lot manufacturing just-in-time
At subcontractor Harbec, where Kappius components are manufactured, Keith Schneider and Jeremiah Wackerman are in charge of the laser-sintering operation. A typical order of ten drive-train assemblies requires two builds on Harbec’s EOSINT M 270, a DMLS system from German-based EOS GmbH, the developer of the technology. Experienced operators working with manufacturing software arrange the components on the machine’s build platform to maximize output: 10 outer rings, 10 inner rings, and 80 pawls (eight for each assembly), plus a few extras.
Since durability was critical for the application, Kappius selected maraging steel, a heat-treatable metal with excellent hardness and strength, from the available materials. Run time is around twenty-five hours per plate, or fifty hours total for ten assemblies.
Following the run, the parts are removed from the laser-sintering unit, machined, and heat-treated, all in-house. On a CNC mill, the manufacturing support structures are removed and an extra twenty-thousandths of material from the backside of the part (added during manufacturing) is planed down. This creates a machined finish. “We use this approach when parts have moving interfaces, such as in this hub or with bearings and bushings,” said Wackerman. “It gives us a really clean surface without imperfections.”
The components are then moved to Harbec’s kiln and hardened to a value of 52 Rockwell C. “We’ve done quite a bit of R&D on maraging steel,” said Wackerman. “We have a heat-treatment method where we are able to minimize any movement, shifting or warpage and maintain precise dimensions while still getting the hardness that we want.”
Kappius is pleased with the results. “The tool steel is super strong,” he said. “I haven’t had a single hub failure.”
And with Harbec supplying parts on an as-needed basis, the father-son team assembles components in their home shop after hours and ships them out to early-adopter cyclists around the world.
As a plastics injection molder, tool builder, prototyper and machine shop, Harbec complemented its traditional manufacturing capabilities by adding DMLS about five years ago. The biggest impact to date, according to Schneider, has been on their injection molding business, where laser sintering has substantially increased design freedom and improved manufacturing efficiencies.
The benefits of DMLS for the bike-hub creator? “Number one is design freedom,” said Kappius. “Number two is the material strength. Three is lead time.”
And then there’s also the rider experience. “People just love the hub,” said Kappius. “They’re faster and fun to ride.” MPF
A brief history of hub innovation
According to Russell Kappius, founder of bike-hub-manufacturer Kappius Components, after flat tires and broken chains, a damaged hub is the third most common way a bike can fail when you’re out on the trail or road. “If you break a hub, it’s a show-stopper.”
Kappius also noted how every bicycle component has advanced toward lighter materials and oversized designs in the last quarter century–except the hub and drive assembly. “In general, hubs used a free-wheel assembly for the rear gear cluster up until the mid-1980s,” he said. “Then the biggest manufacturer in the industry introduced a new integrated free hub, which was an improvement but also forced the industry into a small form factor for the drive system. We’ve all adhered to that standard for the last 25 years.” Until now.
“My hub breaks the rule and uses an oversized interface.” It’s also built around a drive train with more points of engagement (240) in a single revolution of the wheel than what is found in the next closest competitor (120), as well as in most other standard drive trains (18-36). In the Kappius product, the pedal can engage every one-and-a-half degrees and give the rider an extra quarter- or half-pedal stroke, which is great for racing and highly technical riding.
Mold making and DMLS
“Our primary business is plastics injection molding,” said Keith Schneider, DMLS expert at Harbec. “We got into direct metal laser sintering because our owner was interested in building mold cavities and mold cores using this technology.”
Three factors inherent in the technology influenced their decision: a decrease in waste as compared with subtractive CNC processes, faster production of molds, and the design flexibility that sintering provides tool designer/mold makers for conformal cooling strategies.
Because DMLS can create complex geometries, laser-sintered cooling channels are able to closely follow the contours of a mold’s cavity surfaces. This increases the surface area of the channels and improves the efficiencies of the cooling process. It’s a simple principle: When channels conform closely to the product, the part cures more evenly and the cure time is reduced.