From the MEWS archive, a Theseus double acting slide valve horizontal stationary steam engine by H C Roughton to the Edgar T Westbury design. Westbury designed this simple model to be constructed without castings. Bore is 3/4” and stroke 1”.    The Perseus version uses castings.

Westbury was a prolific designer and builder of notable model steam engines, I/C engines, tooling, and more. His drawings are available. His models are with the Society of Model and Experimental Engineers.

Below: Westbury with Theseus.