Thank you, again, Isaac Oleg, for your far-ranging comments. One phrase particularly caught my attention and initially baffled me: "grands, with their combs and one long horizontal center..." The AC is broken and something in the humid heat-bath I'm immersed in tonight has melted some flexibility into my random access processor. Suddenly, I get what you're referring to.
In fact, we have a Pleyel upright in the shop at the moment that employs the comb system for attaching action parts. The hammer butts and whippens are strung on sectional centerpins and each pin is clamped between an action-wide brass rail and sectional pieces with matching tines. Further, spacing and shape of the tines position the parts, limit their side-travel, and facilitate agreement between rails - a brilliant solution to the high cost of traveling, squaring, and spacing parts. Because hammer clearance in is a higher priority than best address of hammers to strings in this piano (hammers 1-40 have a 30 degree flare!), the hammer crowns were filed unsquare to match the plane of the strings at strike. This system presumably took less skill to assemble. prep, and regulate, less time, as well, and therefore cost the company less money to produce.
But simplicities of travel and spacing in the factory present challenges to the piano technicians who later have to service them (although less need for service is a selling point of this system). A general blackening of shanks has occurred during this piano's long life, including some proper charring, an indication of difficulties keeping what was above the comb tidy. Inconvenient maintenance was ignored in favor of producing an inexpensive piano that could still make a profit. As Isaac noted, this is not a reasonable tradeoff for expensive grand piano manufacturing. Unstringing and restringing a section of hammers from their common center pin for a pre-concert repair?
Anyway, we started off hanging hammers to match what we found in the piano and ended up being confronted by the tilt these hammers were assembled with in production. A decision to match crowns at strike with the general plane of the strings (putting my money where my mouth is?) produced a huge squaring overhaul, followed by an equally huge spacing orgy, followed by some adjustments to hammer shape for clearance. Thank you, Ben Webster, RPT (from Gloucester, MA) for being the hands and patience that executed this plan! The extreme wear of the original hammers had obscured the compromised nature of the factory setup. The hammers had been "miss-filed" (IMO) to accommodate the strings for economic reasons, not best musical interests.
Look at this hammer butt, though:
It was elegantly designed to do exactly what it needed to do, fitting into a least space, with simplest assembly. Manufacturing complex shapes was not a problem for Pleyel. But for me, fixturing to bore the several that needed new shanks? Nothing about them was square. So, this small French upright displays a curious intersection of high craftsmanship and budget considerations. On top of these choices, they added over-dampers to the mix...
The sound at setup, with the hammers skewed (but not filed to fit), was terrible. The sound, now that the squaring overhaul has been invoked, is musical. An early gauge was the lowest monochord bass notes who went from sounding tinny to having a gutsy voice with great projection. Ray Negron (http://www.ronsenhammer.com/) made a wonderful set of Weikert felt hammers. But some artful sculpting was necessary, in the end, for many hammers to clear... Clearly there is cost to unfudged hammer-string-fit, but I've found the payback musically worth it.