I've been wanting a thumb for my excavator for some time. I don't have an auxiliary hydraulic valve available, but even so a manual thumb seemed like it would be very useful for handling logs, brush, and rocks around my property.
Honestly the reason I hadn't tackled this project sooner was that I had it in my head that I'd make it from scratch, but then when I looked in to it, it turned out that I could buy a thumb from Amazon shipped to my door for less money that the steel would have cost me. I have no idea how that works, but hey, it saved me a bunch of work so who am I to complain?
In this video I unpack the thumb, modify it to add a pinoff location to stow it folded back, then weld it to the excavator. And yeah, I definitely should have done this ages ago. This thing is so handy (no pun intended). I use it all the time and it works great.
As predicted, two of my three retaining pins disappeared in short order. I replaced them with M6 socket-head cap screws with nylocks and those aren't going anywhere. Luckily the top one stays put (since it doesn't get hit by branches and dirt as I use the machine), and that's the one I need to pull to stow the thumb, so it's the only one I can about being easily removable.
Also, to their credit, Central Welding Supply was willing to work with me regarding my shielding gas issue. They didn't go so far as to refund me, but they knocked 15% off my next exchange, which is more than they had to do (since I failed to check the pressure on receipt it's really on me). I'd still have preferred a full bottle from the get-go, but they were suitably invested in customer satisfaction, even for a tiny customer like me, so that's nice.