Engineering Puzzle.... Archimedes Screw?
Bear, you asked if this rusty post-hole digging tool left for you by the previous owner would work.
My first thought was that it was just an older version of the classic post-hole digger that I used for years similar to the red and black one pictured here.
I mistakenly guessed that the complicated, rusty mechanism would somehow allow the two “shovels” to articulate inward to grip dirt while removing it from the hole.
Boy, was I wrong. You called it an “Archimedes Screw” and sent me some more photos. I magnified them and here is what I found:
First, the two shovels are actually two pairs of shovels. One set is bent inward enough that they meet at the center of the hole being dug.
In fact, they are notched so that their points essentially join at the axis of rotation. This pair will cut into the dirt at the center of the bottom of the hole. The other pair of shovels follows by cutting a wider hole. As the drill head penetrates the earth, it scrapes neat a hole the size of the planned post. The dirt loosened by the drilling can be pulled to the surface by lifting the tool out of the hole.
But there is more.
This digging tool can be adjusted to dig three different-sized holes by simply repositioning a single bolt.
The complex castings of the rusty old mechanism are gently curved so that as the size of the hole changes, the inner shovels maintain their relationship with their points notched firmly together.
A few observations: The tool would have been costly with several fussy castings as well as the hardened steel “shovels blades.”
Also, I presume it was designed for use on the open prairie where few large roots would be encountered. The modern post-hole diggers spend a lot of time being slammed into the hole to cut roots.
Also in the open prairie, the topsoil would be several feet deep with few if any rocks.
Bear, my thanks for this engineering puzzle. Dad
