Click on the short vertical rod above or at the right to see how the mechanism works to rotate the diffraction grating. The design is simple, the cost is cheap, and the performance is excellent. I enjoy doing this kind of design, particularly for instruments that will be used in a teaching situation.

The design of small linkages and parts for use in chemical instrumentation is a critical aspect of whole instrument design. The larger layout of an instrument is actually the simpler design. It is after the whole layout has been done that the difficult task of making the pieces fit and function together within the overall design constraints begins.

A particular example is shown here for the "Heath Czerny-Turner Monochromator". In this instrument he diffraction grating was rotated with a sine-bar linkage. Competitive commercial devices involved optical flats and high sphericity contact balls, which were very expensive.

Instead, in this instrument, Jack Haynes and I used two precision ground orthogonal cylindrical rods (called "crossed pins") attached to the lead screw nut and sine bar end, as shown in the isolated view below.