By Michael Jermann, Assistant Editor
DEWALT’s lead design engineer for drills was tasked with designing a high power right angle drill that is lightweight, compact, and portable. As is common with hand power tools, the goal with the design was to maximize performance while minimizing the size of the tool.
The design would incorporate a mechanical clutch built to limit maximum torque output to 70 ft-lb. Absent the clutch and with a gear reduction of 75:1, the drill would produce a lock rotor torque at the spindle of 175 ft-lb, which would be transmitted directly to the operator of the tool. Compared to conventional coil springs, disc springs offer a higher load capacity in less space. Additionally, the life and performance warranty of the tool were reliant on the disc spring design.
Early on in development, DEWALT’s engineers were working with a low cost disc spring supplier. They had developed and theoretically calculated the initial disc spring design. The first prototype built failed, with the new design achieving less than half the targeted cycle life. Analysis indicated premature fatigue failure of the disc spring was due to higher than expected stress, lesser quality material, and a less than ideal manufacturing process by the original supplier.
Determined to find a solution, the lead engineer on the project contacted Spirol to discuss the disc spring design. Spirol’s Application Engineering team evaluated the design objectives and constraints and determined a standard disc spring could not meet them. The application engineers focused specifically on the disc spring portion of the design and recommended a custom disc spring design that had alternate dimensions, material, and secondary operations. For this demanding and high performance application, these features added significant value and ended up costing only pennies more compared to the product offered by the original supplier.
By partnering together, they determined the best disc spring design for the new angle drill, minimizing costly development time for both companies.
Filed Under: TECHNOLOGIES + PRODUCTS, Design World articles, Gears • gearheads • speed reducers