The Wobble Disk Roaster: How a Retired Designer Created a $150 Home Roaster
Somewhere in New Bern, North Carolina, a retired power-tool designer named Larry Cotton has spent 15 years solving a problem most home roasters know well: how do you get beans to brown evenly without spending thousands of dollars?
His answer involves a flour sifter, a pizza pan, and a disk that wobbles.
The Nutating Disk Solution
The wobble disk roaster uses a deceptively simple mechanism. A metal plate at the base of a cylindrical chamber nutates — tilts and rotates simultaneously — keeping coffee beans in constant motion without paddles, drums, or complicated airflow systems. The beans tumble across the wobbling surface, cycling through the heat zone repeatedly for even development.
Cotton built the first working prototype from an 8-cup flour sifter with the disk cut from a 13-inch pizza pan. The chamber sits above a heat gun base, with temperature control achieved by adjusting the distance between heat source and chamber. Chaff exits through the open top.
Before settling on the wobble disk, Cotton experimented with spinning baskets and rotating dog bowls. Nothing worked until he tried the nutating plate. “The wobble disk stayed in the picture forever,” Cotton told Daily Coffee News. “It did a really good job of circulating the beans.”
$100-$150 Gets You Rolling
The complete build requires a low-cost motor, heat-gun heating element, fasteners, wiring, and a basic frame. Total cost runs between $100 and $150 for a roaster that handles approximately 350-gram batches — roughly three-quarters of a pound of green coffee.
That’s a fraction of what entry-level commercial-style home roasters cost. The Behmor 2000AB runs around $550. A Gene Café 101 hits $700. The Fresh Roast SR800 sits at $300. Cotton’s design lives in DIY territory where popcorn poppers and heat guns meet actual engineering.
Open Source by Choice
The wobble disk design was patentable early in its development, but Cotton chose a different path. He documented his work in Make Magazine and on Sweet Maria’s Coffee website, sharing schematics and build details freely. The design spreads through DIY forums, YouTube videos, and maker communities rather than conventional retail channels.
Cotton identifies first as an industrial designer — he spent his career developing power tools — with coffee as a secondary pursuit. His wife is the coffee enthusiast in the household. His other projects include clock building and music, suggesting a tinkerer’s approach to problem-solving rather than a commercial ambition.
Why This Matters
Home roasting sits at the extreme edge of specialty coffee. It’s where people who care deeply about freshness, origin, and process take full control of every variable. But the equipment gap between modifying a popcorn popper and buying a proper sample roaster spans hundreds of dollars.
Cotton’s wobble disk fills that middle ground. It offers the bean agitation and temperature control of serious equipment using materials available at any hardware store. The design works not because it’s sophisticated, but because rotating and tilting a disk turns out to solve multiple roasting challenges at once: bean circulation, heat distribution, and chaff separation.
The open-source model means improvements accumulate across the community. Someone figures out a better motor mount, posts it online, and the design evolves. There’s no corporate roadmap, no planned obsolescence, just a retired engineer who decided the right thing to do was share what he’d learned.
Specialty coffee has always attracted people who want to understand every step from seed to cup. The wobble disk roaster offers them another step to master — and at $150, the barrier to entry just dropped significantly.