Making an Auger (feed conveyor) from Washers ...and mathematics!

To make a

feed

screw or screw

conveyor

there are two main methods. You can start with a solid bar and machine the material, which is time-consuming. I know. Or you can make a spiral and weld it to a rod or tube. A common way to do this is to start with

washers

. Cut them. And stretch them. But the problem is that if you start with

washers

of a known inside and outside diameter, as you stretch them lengthwise, both the inside and outside diameters will shrink and no longer fit. To begin with, the washing machine needs to be larger so that it shrinks to the correct size when stretched.

There must be a mathematical relationship between the required pitch and the radius of the helical strip when flattened. There is. According to the Encyclopedia Britannica   it is 4 pi squared r above the square bracket h squared plus 2 pi r squared squared near the square bracket   but I couldn't seem to get this to work. Produced rings that were too big. So I came up with my own formula based on the relationship between the lengths of the inner and outer helical paths. This produced rings that when stretched fit together perfectly.