When an engineer-inventor came up with an idea for a low-cost, hobby-grade CNC milling machine, he devoted his spare time and tight budget to making it a reality. To help support this endeavor, Jeff Kerr, owner of PIC-Servo Motion Control in Bellingham, Wash., used the online service ZoomRP.com to make a prototype of the machine’s spindle-motor chassis using the PolyJet rapid-prototyping (RP) method.

“I selected ZoomRP.com because of its low prices and straightforward online quoting and ordering features. The prototype helped me stay on task, test the milling machine, and determine if I needed to adjust the design. In addition, the PolyJet method produced a chassis with tight tolerances, which helped me ensure that the fit-up of the motor spindle to the main motion components was exact enough.
After sending ZoomRP.com the STL file, Kerr received the two halves of the chassis the next day. The parts fit together perfectly with no redesign or adjustment.

The CNC’s spindle motor runs at speeds exceeding 15,000 rpm, so the motor can heat up. The PolyJet material, although accurate, softens when heated. “PolyJet, thus, wouldn’t work well to build the final component for the production unit,” says Kerr. “But the prototype let me ensure the design was right. Should I decide to do another round of prototyping in a higher-temperature material, ZoomRP.com also provides sintered nylon.
The service’s low cost helped Kerr keep the machine’s price to less than $500, important because at this sticker, almost any hobbyist or craftsman can afford one.

Also helping keep project costs in check were the materials the machines would work with, which eliminated a need for a machine with high rigidity. Most hobbyists work with soft materials such as wax, ABS, wood, and urethane foam. Much of Kerr’s design effort, thus, went into an accurate motion system. Additionally, because craftsmen generally make small parts such as jewelry, figurines, and decorative soaps, the CNC’s working platform is small — 5.5 × 3.5 × 4.0 in.

The online service ZoomRP.com, comes from Solid Concepts Inc., 28309 Avenue Crocker, Valencia, CA 91355, (661) 295-4400, a supplier of rapid prototyping, direct digital manufacturing, tooling, and injection molding services.

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