I used to hang my blunders proudly on the wall of the shop, in an attempt to keep me humble.
. The problem quickly became, there were so many of them I was running out of room
since then I've "thinned the herd", keeping only the colossal blunders.
In this area, my prized possession is the leading frame member of the Allen 10-wheeler I built as my first machining project so many years ago. This was the first casting I attempted, and of course I mucked it up.
My problem was that in my concentration to make sure I had measured it properly, so that all the surfaces on the drawing were accounted for, I missed seeing that I had mounted it to the milling table at a somewhat crooked angle. As I milled across the top of the casting, much to my chagrin, I ran out of material before attaining the length measurement I needed.
Much distraught, I called Gene Allen, the supplier of the castings, and told him what I had done and asked if I could purchase a replacement casting.
Gene's response was, "a 'good machinist' could salvage that".
My reply was, "Gene, you're not talking to a 'good machinist'".
There was a moment of silence on the phone, followed by raucous laughter, but I did get my replacement casting.