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Medicine is undergoing a transformation toward minimally invasive surgery, and with it comes an increasing need for more precise miniature instruments to accurately execute complex procedures. In catheter-based surgeries, the physician must control the tip of the catheter from a distal point outside the body, which makes it difficult to achieve precise manipulative control. Providing actuation local to the desired point of manipulation will greatly improve the physician's ability to intervene on diseases in a minimally invasive fashion. We present a new actuator made from laser machining shape memory alloy (SMA) tubes for use in an active steerable catheter. Using finite-element analysis and experimental verification, we have designed a 1.5-mm-long SMA actuator cut from 1.27-mm-diameter NiTi tubing that exhibits good fatigue properties, and can produce forces of 12 N at 20% elongation. We use an iterative rapid design process, so that many actuator geometries can be tested quickly to achieve the desired mechanical properties without complex material models. In this paper, we describe the design and testing of the actuator, and verify its force, elongation, and fatigue properties.