There was a thread re determining key height recently. Most were agreeing that parameters of the action cavity determine how high or low, the "as-built" piano will allow you to set key height. The determining factors were:-what is the space between top surface of the keys at rest and the bottom of the closed/felted fallboard-what is the height of the top of the keyslip in relation to key top at full dip (meaning you don't want to key to hit the keyslip, at full dip)-keeping the number of punchings at the balance rail pin minimized (meaning a large stack of punchings is not a stable situation)-reducing thickness of backrail cloth allows one to raise key height, without adding too many balance rail punchings, if too many punchings is looking like a problem-assuring chosen key height will allow you to regulate the key at the chosen dip (meaning, make sure there is enough height to allow adequate numbers of front punchings to accommodate inconsistencies...one does not want to find 3/4 of the way through the entire regulation, that the key height on 5 oddball notes does not allow you to achieve required dip...requiring you to raise key height and undo huge amounts of your regulation)What we didn't discuss is that the above may appear to suggest that action cavity dimensions, ie distance from keybed to bottom of fallboard at rest, keyslip height, and spreader distance to keybed, are always nice and parallel. While it would be nice for the action cavity given dimensions to be parallel and consistent, parallel is an anomalous condition in the majority of pianos. Assuming parallel, has a way of kicking one in the butt down the line. That is, no dimensional assumptions can be made in restoration work, especially when it comes to forefinishing.One must correctly ascertain the non-parallel aspects of the action cavity first, placing the finished/felted cheek block and fallboard and slip in place, and measuring at multiple places before deciding what dimension you are actually working to, in order to ascertain key height. Compromise describes the normal state of affairs in determining what dimensions will be held tight and what dimensions will be massaged.I just had this come up in a piano I am wrapping up...well actually it comes up in every fore finishing job, but this came to mind because of the recent thread. I played the chess game, trading off the various action cavity givens and inconsistencies, and arrived at a workable solution for key height. However, is was just barely workable. I knew the fall board was not parallel to the keybed by about 2mm at its worst. Came up with a compromise key height, and it regulated...but just by the hair of my chinny-chin- chin.
The client finally added the replacement of the whips, after seeing the rest of the instrument blooming. I went back and re-did much of the regulation, and revisited key height...raised it .020 at the treble, and after much thought, raised the bass an unequal amount, .040 as the fallboard was off. Bass section has a bit too many balance punchings for my liking, but the other 3 sections do not have too much. There is a little more room for front punchings now, and the gap between fallboard and top of keys is better and more consistent.
What I really should have done, way back at the beginning, is re-set the fallboard height, or used a non-standard key end felt to lower the back of the keys. But back at that point, which would have been early in the rebuild, it is really hard to know what final regulation dimensions will be, as the action wasn't rebuilt yet...you get the picture...the chicken and the egg. Sometimes, given all the unavoidable inconsistencies, making the proper decision is easier in hindsight, than it is in the heat of battle. Both of my key heights worked, but my preferred solution would have been to change fallboard height, or key end felt, way back at the beginning. Of course, then, if I had moved the fallboard I would have had to prove it still closed properly.Just a post to illustrate how interactive such a simple decision as key height, actually is, rather than just saying " in all Steinway's, key height is xyz inches".