In his later years (and as dementia was beginning to set in) my dad spontaneously decided to start building acoustic guitars in all sorts of shapes and sizes, trying out various weird ideas he had. He hugely enjoyed it and it's left behind some interesting heirlooms and a legacy that he otherwise never expected to leave. A piano is at a different scale (pun intended) but if you have a modicum of practicality, you can build something like that with enough time.
I had a similar experience with my grandmother. Her motivation and curiosity left her. I tried to interest her in new things a number of times, thinking she'd be so much happier. The data, though, led me to decide she was in fact happier when I just accepted who she had become.
This is my greatest fear, more than death: to stop learning, to stop creating, to stagnate. I wonder if nutrition or exercise has an impact on this. I would eat broccoli every day if I thought it would improve my chances.
Hmm, maybe try figuring out what things he likes and/or can engage in without effort - whatever he can do well without thinking.
And maybe track this over time. Borrowing the analogy of HDD/SSD corruption, which can impact critical filesystem metadata just as easily as file contents, it's impossible to predict how that fundamental capacity to engage will shift and change in confounding and lateral ways.
and access to either some very enthusiastic amateur smelters, one enthusiastic professional smelter, or some really good welders, because wood you can easily find, but a pre-cast plate for an unusual size piano... very not so much.
I'd think that welding would be the sensible route if you're just doing one, as long as it's made sturdy enough. Casting the whole frame in one piece makes more sense if you're mass-producing pianos. Also, it's traditional. I don't know what welding equipment was like a hundred plus years ago during the piano-manufacturing boom, but casting piano frames was a well-honed art.
Better be really well-engineered as the the string tensions on a conventional grand piano ranges into the low 10s of tons. Yamaha pianos, for example, are around 20 tons.
