Impact absorption drive mechanism for a reciprocating tool

What is this patent about?

’547 is related to the field of power reciprocating tools, such as saber saws and jigsaws, which convert the rotary motion of a motor into linear back-and-forth motion. In these tools, a common failure point occurs when a saw blade suddenly binds or jams in the workpiece, sending a high energy impulse back through the mechanical linkage. This shock often results in catastrophic failure of the drive train, typically manifesting as stripped or broken teeth on the internal gears.

The underlying idea behind ’547 is to integrate a shock-absorbing element directly into the mechanical path between the blade and the motor to dissipate sudden kinetic energy. Rather than relying on external clutches or heavy damping materials, the invention utilizes the geometry of the drive components themselves to create elasticity. By modifying the structural members to allow for controlled longitudinal expansion and contraction, the tool can absorb the impact of a blade bind without transferring the full force to the delicate gear teeth.

The claims of ’547 focus on an elongated, hollow plunger that features a spiral slot cut through its cylindrical outer wall. This slot wraps around the circumference of the plunger for multiple turns, effectively transforming a section of the rigid drive rod into a high-strength spring. The claims specify that this compliant section is permanently integrated into the plunger body between the drive connection and the blade attachment point, ensuring that the structural integrity required for cutting is maintained while providing a dedicated zone for energy absorption.

In practice, the invention works by allowing the plunger to momentarily change its length when the blade encounters extreme resistance. Under normal cutting loads, the steel wall of the plunger is stiff enough to transmit the motor's power efficiently. However, when a bind occurs, the spiral geometry allows the plunger to compress or stretch slightly, acting as a mechanical buffer. This momentary deformation absorbs the peak force of the impulse, protecting the wobble plate or crankshaft drive mechanism from the sudden spike in torque.

This approach differs from prior solutions that typically used slip clutches or rubber isolators, which can wear out or add significant bulk and complexity to the tool. By using a compliant configuration machined directly into the plunger or drive link, the invention provides a lightweight, maintenance-free method of shock protection. It effectively turns the primary reciprocating member into a dual-purpose component that serves as both a rigid drive shaft and a protective shock absorber.