It says it needs obsidian to repair if I add the obsidian pick axe head
with any tool, sword, anything Tinkerer's:
1) get to were you can see some zombies at night.
2) Make a 2 high nerd pole.
3) Swing at their heads.
4) PROFIT
Even the obsidian one will upgrade in no time - hope and pray you get a HUGE wave, works wonders.
I would even take 2-3 tools with you, or build a platform you can build new tools on.