A chainsaw, compressor or pen are examples of mechanisation, not automation. They replace part of the human effort needed for a job, making the remaining human effort even more valuable.
Automation fully replaces human work for a given job. It's a difference in kind.
However, automation may replace only some jobs in a value chain, making the remaining ones even more productive and valuable.
A fully automated value chain is a difference in kind again.
The word "auto"(oneself), often used with meaning to do by itself.
Automation is a very broad term, which mechanization is a part, but not a requirement of.
Anything that moves work from human to other forces is automation, having a thing do things by itself. An automobile is the automating of our movement.
There is an interesting distinction used by some economists between "labor-saving"/"captial-augmenting" technology and "labor-augmenting" technology: the former encourages you to decrease headcount, while the latter nets you more units of work completed per unit of labor.
Automation fully replaces human work for a given job. It's a difference in kind.
However, automation may replace only some jobs in a value chain, making the remaining ones even more productive and valuable.
A fully automated value chain is a difference in kind again.