Well Chris, "designing" is a loose term with me. I do love however seeing how one item can serve several functions. At photo shows I'm the guy rummaging around in the big plastic buckets, full of series adapters, old flash brackets, broken pieces of "I dunno, beats me" stuff. All marked for 25 cents to a dollar or so.
This is not a lonely undertaking. Quite a few of our members are very handy and show some pretty good engineering skills but I'm more of a dreamer and backyard inventor.
My latest "thing" is a bellows mounted 90mm f4 Elmar that will focus from infinity to 1:1 on a third party monorail bellows for my Olympus Pen F. It all started when I discovered that the lens head from my 90 Elmar would screw down and seat nicely in a series 5 thread. It's not the exact same thread but as I say it will spin on and seat. And of course it still works fine on the Elmar focusing mount. Years earlier, from one of those plastic bins I had picked up the bellows for $2 because "Hey, I might need this some day" The other parts were; the back end of a 'T' mount for Pen F, a series 6 to series 5 step down ring, a 34mm to series 6 adapter and a bit of aluminum sheet, and a few brass 2-56 flat head screws. All, except the screws, from my photo junk bin. With a series 5, plus 10 close up lens mounted instead of the Elmar, I have a dandy 100mm f3.8 soft focus lens too.