What this article is about is a simple system that provides kinematic support and adjustment in all six axes of movement. To refresh your memory on all the possible movements , there are three translational movements that most machinists are familiar with, X, Y, and Z. and three angular which airplane pilots are familiar with are pitch, yaw and roll. These are defined by rotation about one of the translation axes. In an airplane the orientation of the angular movements is determined by the direction of flight. Each branch of technology has a convention for "normal" positions of the axes to further confuse us poor mechanics on the six degrees of freedom.
beamline elements and provide a simple way to adjust and maintain their alignment. This setup is simple and clever and more than likely has uses outside particle accelerator construction. The basic parts are just glorified garden variety turnbuckles. Instead of real turnbuckles we use stiff precision rod ends in our six strut systems to rigidly isolate sensitive equipment from vibrations transmitted through the floor. At the same time the six strut system provides precision adjustment and allows us to position equipment in all six axes to less than .001 inch easily.
Stewart Platform. Sometimes it is also referred to as a hexapod. Hexapods are also a positioning system that locates parts fully with six degrees of freedom. Its main drawback is higher expense and practical implementation for day to day applications. Furthermore, it lacks the easy intuitive adjustability of the turnbuckle six strut system.
differential thread struts where both rod end threads are right handed but the thread pitch is different. Differential same direction threads cancel each other with the net movement coming from the differential between the two thread pitches. Very small per turn movements can be designed with the proper choice of threads. The choices in thread pitches are limited if you stick to standard rod ends but for special situations they are simple enough to modify or custom order from the manufacturer.
So if you want to try this odd looking but clever system out here are a few general guidelines.
Keep the struts orthogonal to one another. Three in the one direction where rigidity is most important, two in the second direction where you need some translational control, and one in the direction of least need of rigidity and translational control. Use the longest struts that are practical. This reduces the crosstalk between the axes of movement from angular changes. Mount the rod ends of the part that moves so that their centers are in plane with the features you are trying to align.
This is a very forgiving, inexpensive alignment system that is capable of superb accuracy and control. Next time your backed into a corner and have your back against the wall, pull this clever solution out of your hat. Or better yet when somebody throws a hexapod out as a possibility drop this into the discussion. At first pass it looks a little wacky but trust me it is tried and proven a thousand times over. From a design point of view it is simple and elegant with no more parts than is necessary to get the job done. When is the last time you could say that about set screws and slotted plates?