In kinematic applications, plane flat surfaces have a higher load carrying capacity than cylindrical or spherical ones. Flat surfaces with very fine surface texture are quite slippery, so they provide excellent alignment of the mating spheres. Producing high quality flat planes on prismatic devices requires a unique approach. Lapping the inside flat faces of a Vee Block or even worse the inside faces of a Trihedral Cup is not at all a practical task.
An approach that can produce the highest quality internal prismatic devices is the split design. Instead of constructing the device as a monolith, which is conventional wisdom, each facet of the prism is produced as a separate but symmetrical unit.
A very high quality flat facet can be easily produced on the truncated surface of a cylindrical post. Rigidity is not lost by splitting the faces of the prism, because the cylindrical design provides a simple method for extremely rigid mounting. By machining a trench in the Kinematic Platform with an end mill that has the same radius as the cylindrical post itself, and gluing the assembly together under load, an extremely rigid assembly results. The reason that this design can so far outstrip the rigidity of a monolithic component is not so obvious; but it is due to the inherent weakness in the joint connecting the monolith to the Kinematic Platform.
For light loads, there is seldom any reason to use this more complicated flat facet design when three spheres will form an excellent trihedral cup and two cylinders a fine Vee Block.
A universal component that will fill a broad array of high load kinematic applications is a three-quarter inch diameter (19mm) cylindrical post that is truncated at a 45-degree angle. This one component will function well with any ball size from one half inch (13mm) to over one inch (25.4mm). Better repeatability can be achieved by using a steeper angle but this will reduce the load carrying capacity.
These components can be produced for surface mounting by drilling and threading a hole in the flat base but in doing so much of the system’s rigidity is lost.< Because the relative cost of raw material is rather small in relation to the overall cost of this component, tungsten-carbide, with its tremendous stiffness–or Young’s modulus of elasticity of 98,000,000 P.S.I. and high hardness of 91-HRA–has been chosen as the standard material.
There is wide latitude of design options of both size and materials to cope with different loads, corrosive environments, temperature, as well as magnetic and electrical qualities. We will custom build just about any design to fill specific customer needs.
The average price for a steel Prismatic Post is $45.00 each.