"linear friction welding" (lfw) is similar to spin welding, except that the moving chuck oscillates laterally instead of spinning. the speeds are much lower in general, which requires the pieces to be kept under pressure at all times. this also requires the parts to have a high shear strength. linear friction welding requires more complex machinery than spin welding, but has the advantage that parts of any shape can be joined, as opposed to parts with a circular meeting point. another advantage is that in many instances quality of joint is better than that obtained using rotating technique.