I don't think that's quite the right way to ask the question.
First, a smooth front weight (FW) curve results when there is a smooth strikeweight (SW) curve, the Action Ratio (AR) is exactly the same from note to note, and the balance weight is also uniform. Any irregularities in the SW curve, AR or a Balance Weight (BW) that is not uniform will result in variations in the FW curve.
The strikeweight curve can be easily measured and controlled, short of measurement error. In a weigh off to determine the BW (again assuming no measurement error of the DW and UW), the BW can be uniformly set. The AR is never exactly uniform note to note due to inevitable execution irregularities in things like capstan line, balance rail pin locations, knuckle hanging, punchings, etc.
So if you are going to set a smooth FW curve to parallel the SW curve exactly you will always have some irregularities in the BW. That seems unavoidable. The decision to be made, then, assuming you create a smooth SW curve, is whether to compromise a smooth FW curve or a uniform BW. If you decide a uniform BW is important then you will not have a smooth FW curve, it will be a bit bumpy depending on the inconsistency in the AR. If you decide that a smooth FW curve is important then you will have a non uniform BW. The degree to which the AR is exactly uniform will determine how much compromise there is. I generally opt for uniform BW because the effect of slight variations in the FW to inertia is minimal. Where the perceptions of differences in BW occur I can't say, I don't have any real evidence.
The most important relationship in setting up an action is the AR to the SW as that determines the inertia, which will always be greater in the bass than in the treble (due to greater hammer mass in the bass). That relationship also determines the general amount of lead required to balance the action at a given BW. Excessive FWs, or too many leads, result from a poor relationship between AR and SW. High inertia in the system, or a heavy feeling action, is not primarily due to too many leads, it's due to the poor AR/SW relationship. Too few leads, or too low a front weight is also not good as it results in inertia that is too low which can leave the pianist feeling like that can't control the action or can't feel the throw of the hammer. Low inertia actions that come about as a function of very low ARs also can require excessive key dip as the hammer travel is reduced relative to the key travel the lower you go. That can also be unpleasant.
I have found that the simplest indication of whether that relationship between AR and SW is ideal in the Stanwood system is to use the FW maximums as a guide. Approximately 80-85% of the FW maximum as indicated in the Stanwood system places the action in about the ideal place or, as Fandrich and Rhodes put it, "An action to die for". Actions are certainly acceptable within a range of that target but I generally try not to go outside of 75% - 90% and generally try and hit that 80-85% target. In addition I usually aim for that in the middle section(s) of the piano. If my SW curve, assuming it's a relatively normal range, pushes the FW up a bit in the treble, or down a bit in the bass outside of that ideal range I don't really think it's of much consequence. Again, the inertia will always be lower in the treble and higher in the bass anyway. Aside from uniform BW the pianist will react positively to predictable inertia at a reasonable BW, or in the feel of the throw of the hammer.
So targeting 4 grams under maximum on a note whose front weight max is 20 grams would be exactly 80%. However, four grams under a note that had a FW maximum of 40 grams would be 90%, and 4 grams under a note whose FW max is 5 grams would be 20%. So I don't think the 4 gram target makes sense except, perhaps, in the center of the keyboard.
My preferred method then is to determine the AR/SW relationship that produces in the center of the piano a FW of 80-85% of the Stanwood maximum and I then smooth the SW curve based on the given set. On most sets the hammer weights vary a total of about 5 grams +/- from bass to treble. After everything is installed I generally do a weigh off to calculate the BW on each note, address friction anomalies and then set a uniform BW allowing small variations in the FW curve.
Sometimes, if I find a note that the BW on a given note is too low and would drop the FW too far below the curve that would result from the removal of lead, I might, instead, add back weight to the key--add a lead behind the balance rail. The logic there is that if the SW curve is smooth and the key is weighing off too low it means that the AR on that note is lower than the other surrounding notes. That will lower the inertia on that note. Without altering the SW, the best way to compensate for that (i.e. to add inertia) is to leave the amount of lead in the front of the key in the general realm of the FW curve and add lead to the back of the key to satisfy the BW requirements. That additional lead will then not only satisfy the BW requirement but add some inertia. Probably not quite enough as the leads aren't responsible for that much of the inertia, but it will add some.
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David Love RPT
www.davidlovepianos.comdavidlovepianos@comcast.net415 407 8320
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Original Message:
Sent: 03-01-2021 17:18
From: Floyd Gadd
Subject: Front Weight Tolerances
I have been gravitating toward David Stanwood's concept of a chosen smoothly scaled front weight spec as a design feature. I have also been paying attention to Nick Gravagne's series in the Journal where he describes the reduction of front weight as a combination of removing key leads, and drilling out lead for subtler adjustments.
Somewhere I recall seeing a clinician speak about reasonable tolerances when modifying front weight. but I can't find that segment as I go hunting in the resources available to me. I high degree of precision is possible, but at what point does one experience diminishing returns? When it comes to front weight, how much variation do you think can be present before it becomes perceptible to a discerning pianist?
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Floyd Gadd
Regina SK
306-502-9103
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