A non-Cartesian coordinate positioning machine that includes an extendable leg assembly for positioning a component such as a measurement probe within a working volume of the machine. The extendable leg assembly includes a first member and a second member which move relative to one another when the extendable leg assembly changes length. The first member including an axial arrangement of magnets forming part of a linear motor for extending and retracting the extendable leg assembly, and at least one resilient member for absorbing at least some of any axial thermal expansion or contraction of the magnets in use.