Low friction shaft support

Each rotating pair enhances an amount of losses due to friction forces between the rotating part (a shaft) and its supports (bushings, sleeves, bearings, etc.). These losses depend primary on the design parameters of the application. There are applications where strength and durability are the main specifications; others are characterized by the increased precision and speed of rotation, or an increased useful life. The rotation with low friction losses is a special specification with a broad scope of application. When designing measurement tools or gauges we need very sensitive instruments, capable of transferring even the smallest different between two positions of a lever or a mechanism. Some will say why you don't use small bearings or these new exotic materials (see ceramics). The answer to this is cost, availability, and size. Unfortunately there are not standard parts for every application (and available to all). How we can make our own low friction supports for our shaft?

The solution is to reduce the supporting surface (responsible for the friction) between the shaft and the corresponding supports. Using a conical surface contact from a cylinder one we reduce the friction a lot and if we use an edge contact from a surface one certainly we reduce the friction forces dramatically.

The first version (see figure below) uses a rotation link which has conical tips at its ends. Each conical tip enters the corresponding conical recess at the end of an adjusting screw (fixed at gauge's body). With the screw we can adjust the sensitivity (related straight to the screw preloading) of the shaft rotation. Correct preloading gives a low force rotation without axial clearances. Using the method of inversion we can design another subversion of the above design. We can make the shaft with conical recess and the adjusting screws with conical tips. The jam nuts maintain the adjusting screw at correct position.

The second version uses the ball tip and conical recess combination. Here the shaft has ball tip ends which enter at the corresponding conical recess of the adjusting screws (see figure below). Like the conical tip version if we invert the design we have a better one with conical recesses at both ends of the shaft (or link) and round tips at the end of each adjusting screw. This inverted design is the one most gauge makers prefer (the link rotates so smoothly particularly if it has a small mass). It's easy to make concentric conical recesses at two parallel surfaces of a link using the appropriate (depends on ball size) centre hole tool. In many gauges designers use separate balls and conical recesses at both link and adjusting screw (avoid make ball tip). Personally I prefer this design with the round tips solid at the end of each adjusting screw because it's easier to assembly (you will never lose the balls!!). The rotating shaft could be separate from the rotating link (like the figures) or it can be a link (lever) with both its opposite sides machined with conical recesses (depends on the sensitivity of the gauge).