Pianotech

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

------------------------------
David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320

Original Message:
Sent: 05-31-2021 11:25
From: Jim Ialeggio
Subject: No key bounce on return

Finishing up an S&S L which turned out to be one of my nicest efforts, with a bunch of stuff happening which are firsts for me. Piano goes out Wednesday, and I've been playing up a storm on it all weekend...don't want it to go away. The level of control this action provides is a serious improvement over already really nice action builds, for me.

There are a couple of things that I want to make sure I carry into all future projects. The first is, either absence of key bounce on return or quieted bounce on action return. The whole thing just feels tight, offering a great improvement in intuitive control in an excellent, effort-less way. I am trying to suss out why.  A combination of lack of key return bounce, super efficient damper shutoff, and belly not breaking up on bass trills makes 2nd octave left hand trills, which are mostly frightfully difficult to control volume wise, utterly controllable. This is something I've experienced only one other time. It was in one of Ed Mcmorrow's B's.

So the possible parameters that accomplished this have to be: Elevated key bushing friction levels, shank friction, overall friction, leverage?...other parameters?  My BW reflect my opinions on action design. So for example:

D4 - BW = 47 (yes Stanwood fans this is not a typo)...pretty standard for me.  DW 58g, UW 36g, friction 11g. No lead in front half of key, FW 14.6g, HW 6.88g (don't measure SW as the measurement is so noisy). Key  bushing friction itself 2.5g, WNG hard bushings shank friction 4g (would prefer 6, but it seems to migrate down)

Key bushing friction - We have been working to tighten up the key bushing fit for a couple of years. Its actually harder than it seems, at least for us, as tight but not too tight is harder to pull off than loose, of course.  But I believe this along with shank friction, which we really try to elevate to 4-6g are key, and a large part of this firmness. However, within this general level of, what I will call, helpful friction, some adjacent keys have literally no bounce and some have a minimal bounce on return. The hammers as well will exhibit bounce motion similar to it's key's slight bounce. I really like the no bounce, but I can't really finger what is different between the no bounce keys and the slight bounce keys. All weight measurements in adjacent keys and friction levels check out to be very similar. Key friction checks out similar.  I did not measure whip flange friction in the as built condition. Balance holes are original to the piano, which got slight usage in its life prior to rebuild. Balance hole fit is a little freer than a new keyset would feel like, but not pulley keys at all...just free...key shoes, but I don't remember what the shoe wood was.

Any thoughts on what parameters effect key bounce on return, especially difference on adjacent similar keys, in an overall firm action?


------------------------------
Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
------------------------------

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Note: I've made some edits and additions since I first posted this 

David:

It's a big topic so let me see if I can explain.  The downweight (from which we derive the balance weight) represents the minimum force required to actuate the key.  That's typically around 50 grams.  We don't actually play the piano with that low a force, that's just the minimum force required to get the key to go down.  The actual force with which we play the key is much greater generally.  The force required to accelerate the key to the maximum speed (to a achieve a forte) is some 20 times that, let's say 1000 grams.  In reality when we play or analyze the piano we are dealing with rotational dynamics and the force to overcome inertia as we have to accelerate this mass which we call a hammer at the end of a series of levers.  The static measurements (BW) we use don't really capture the fact that we have to accelerate the hammer to some velocity in order to achieve the dynamics that we want from soft to loud.  So when we talk about a "heavy action" what we are really talking about is an action that resists acceleration to a level that is uncomfortable.  That level may vary from pianist to pianist, and, of course we can have insufficient resistance too (a fly away action) so our goal in setting up an action is to determine what level of inertia we want more than just getting some downweight target at any expense.

The primary driver of inertia is the relationship to the leverage we have as a product of the three levers (something we often refer to as the action ratio AR) and the mass we are moving at the end those levers.  There are other contributing factors, the key, the wippen, the lead in the keys, but their contribution is much less than the AR/hammer mass relationship.

So the question is how do we measure that and choose the relationships we want.  Programs like Nick Gravagne's actually calculate the inertia and give us a number which he then translates into a set up that is either acceptable or not acceptable .  The inertia numbers themselves are somewhat meaningless to lay people.  The Stanwood system uses a series of static measurements, key ratio, strike weight, front weight, balance weight, wippen weight, etc, from which that relationship is inferred.  The Fandrich Rhodes system ("Actions to Die For" article PTJ) have their own system and reference numbers, which I don't understand the derivation of exactly, but give an indication of whether that relationship is in the sweet spot.

Most people these days are using some variation on the Stanwood system, probably because it involves simple static measurements.  What can be gleaned when you compare these three systems is that the front weight of the key is an indication of that relationship between the AR and (we'll use Stanwood's terms) the strike weight (SW).  An excessively high front weight to achieve a reasonable balance weight or downweight is an indication that the AR/SW relationship is not a good one: that the AR is not adequate to move the hammer mass indicated by the SW.  With further analysis you find that the FW is a telltale sign through the keyboard as to whether that relationship is maintained.  Stanwood has created a chart of what he calls "Front weight maximums" which, if exceeded, tell you that the relationship between AR and SW is poor.  (I'm not sure how he derived those FW maximums but the exact number are not hard and fast but general guidelines).  You can further analyze that along with the "Actions to Die For" and Gravagne programs to find that there is a real sweet spot where the inertia is adequate that the pianist has some sense of the control of the mass they are moving (they can feel it) but it doesn't fight them too much.  That happens to fall when the front weight is at about 80 - 85% of the front weight maximum at a standard BW of about, let's say 37 - 38 grams, or about 50 grams down weight.

Obviously one can choose a different starting point for the minimum force (measured downweight) as Jim has done when he selected a BW of 47 grams, meaning a downweight at D4 of 58g.  But lets imagine that we are trying to achieve the goal of 80 -85% FW Max and a BW of 37 grams.  That would mean, at D4, that we would be on target if we got D4 to a BW of 37 grams with a FW of about 25g (which is about 85% of the FW maximum according to Stanwood charts).

Let's compare that with Jim's action which is a BW of 47 grams and a FW of 15 grams.  Fifteen grams of FW is about 50% of the FW maximum.  If we want to compare the two actions then we have to compare apples to apples so to change Jim's action from 47 grams BW to 37 grams BW we need to add 10 grams of FW which leaves us then with the exact same numbers as the other action.  (The relationship between FW and BW in the Stanwood system is a 1:1 inverse ratio so one gram added to the FW drops the BW by one gram.).

With the exception of the, probably, one key lead that Jim has removed in his 47g BW action with 15g FW, that action will perform with very similar dynamics to the action that has 37g BW and 25g FW.  The difference being the minimum force required to actuate the key (58g v 50g) and whatever the one key lead contributes to a change in the inertia which isn't very much, measurable but not significant.

In summary, I think actions perform best and inertia falls into the right place when the BW at 37 - 38 grams is achieved with a FW of 80 - 85% of the Stanwood FW maximums at least in the middle of the keyboard.  The SW curve, which can vary, might push the extremes of the keyboard into different territory, I don't think it's that critical there.

Below is a graph of the FW maximums.  My approach in setting up an action is to make sure that from, say, notes 20 - 60 I can achieve my medium BW (say 38 grams) with ~80 - 85% of FW max.  I then smooth the strikeweights from there and can modify the BW if I so choose up or down with small changes in the FW max percentage.  That's a pretty reliable way to get consistent actions.  If you decide later that you actual prefer something different, lower inertia, lower or higher BW, etc.,  then you can use that as a baseline.

Basically the lower the FW at a given BW the lower the inertia which means that the top of the piano always has lower inertia than the bottom which makes sense since the hammer mass is less. If you want a lower inertia action then target a lower FW but be careful.  The main way to achieve lower inertia is lighter hammers or lower AR.  But lower AR means either shorter blow or increased  dip and that comes with its own problems. Also note that it is not the lower FW that is responsible for lower inertia   It is the more advantageous relationship between AR and SW that is responsible  The lower FW is a result of that relationship. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Note: I've made some edits and additions since I first posted this 

David:

It's a big topic so let me see if I can explain.  The downweight (from which we derive the balance weight) represents the minimum force required to actuate the key.  That's typically around 50 grams.  We don't actually play the piano with that low a force, that's just the minimum force required to get the key to go down.  The actual force with which we play the key is much greater generally.  The force required to accelerate the key to the maximum speed (to a achieve a forte) is some 20 times that, let's say 1000 grams.  In reality when we play or analyze the piano we are dealing with rotational dynamics and the force to overcome inertia as we have to accelerate this mass which we call a hammer at the end of a series of levers.  The static measurements (BW) we use don't really capture the fact that we have to accelerate the hammer to some velocity in order to achieve the dynamics that we want from soft to loud.  So when we talk about a "heavy action" what we are really talking about is an action that resists acceleration to a level that is uncomfortable.  That level may vary from pianist to pianist, and, of course we can have insufficient resistance too (a fly away action) so our goal in setting up an action is to determine what level of inertia we want more than just getting some downweight target at any expense.

The primary driver of inertia is the relationship to the leverage we have as a product of the three levers (something we often refer to as the action ratio AR) and the mass we are moving at the end those levers.  There are other contributing factors, the key, the wippen, the lead in the keys, but their contribution is much less than the AR/hammer mass relationship.

So the question is how do we measure that and choose the relationships we want.  Programs like Nick Gravagne's actually calculate the inertia and give us a number which he then translates into a set up that is either acceptable or not acceptable .  The inertia numbers themselves are somewhat meaningless to lay people.  The Stanwood system uses a series of static measurements, key ratio, strike weight, front weight, balance weight, wippen weight, etc, from which that relationship is inferred.  The Fandrich Rhodes system ("Actions to Die For" article PTJ) have their own system and reference numbers, which I don't understand the derivation of exactly, but give an indication of whether that relationship is in the sweet spot.

Most people these days are using some variation on the Stanwood system, probably because it involves simple static measurements.  What can be gleaned when you compare these three systems is that the front weight of the key is an indication of that relationship between the AR and (we'll use Stanwood's terms) the strike weight (SW).  An excessively high front weight to achieve a reasonable balance weight or downweight is an indication that the AR/SW relationship is not a good one: that the AR is not adequate to move the hammer mass indicated by the SW.  With further analysis you find that the FW is a telltale sign through the keyboard as to whether that relationship is maintained.  Stanwood has created a chart of what he calls "Front weight maximums" which, if exceeded, tell you that the relationship between AR and SW is poor.  (I'm not sure how he derived those FW maximums but the exact number are not hard and fast but general guidelines).  You can further analyze that along with the "Actions to Die For" and Gravagne programs to find that there is a real sweet spot where the inertia is adequate that the pianist has some sense of the control of the mass they are moving (they can feel it) but it doesn't fight them too much.  That happens to fall when the front weight is at about 80 - 85% of the front weight maximum at a standard BW of about, let's say 37 - 38 grams, or about 50 grams down weight.

Obviously one can choose a different starting point for the minimum force (measured downweight) as Jim has done when he selected a BW of 47 grams, meaning a downweight at D4 of 58g.  But lets imagine that we are trying to achieve the goal of 80 -85% FW Max and a BW of 37 grams.  That would mean, at D4, that we would be on target if we got D4 to a BW of 37 grams with a FW of about 25g (which is about 85% of the FW maximum according to Stanwood charts).

Let's compare that with Jim's action which is a BW of 47 grams and a FW of 15 grams.  Fifteen grams of FW is about 50% of the FW maximum.  If we want to compare the two actions then we have to compare apples to apples so to change Jim's action from 47 grams BW to 37 grams BW we need to add 10 grams of FW which leaves us then with the exact same numbers as the other action.  (The relationship between FW and BW in the Stanwood system is a 1:1 inverse ratio so one gram added to the FW drops the BW by one gram.).

With the exception of the, probably, one key lead that Jim has removed in his 47g BW action with 15g FW, that action will perform with very similar dynamics to the action that has 37g BW and 25g FW.  The difference being the minimum force required to actuate the key (58g v 50g) and whatever the one key lead contributes to a change in the inertia which isn't very much, measurable but not significant.

In summary, I think actions perform best and inertia falls into the right place when the BW at 37 - 38 grams is achieved with a FW of 80 - 85% of the Stanwood FW maximums at least in the middle of the keyboard.  The SW curve, which can vary, might push the extremes of the keyboard into different territory, I don't think it's that critical there.

Below is a graph of the FW maximums.  My approach in setting up an action is to make sure that from, say, notes 20 - 60 I can achieve my medium BW (say 38 grams) with ~80 - 85% of FW max.  I then smooth the strikeweights from there and can modify the BW if I so choose up or down with small changes in the FW max percentage.  That's a pretty reliable way to get consistent actions.  If you decide later that you actual prefer something different, lower inertia, lower or higher BW, etc.,  then you can use that as a baseline.

Basically the lower the FW at a given BW the lower the inertia which means that the top of the piano always has lower inertia than the bottom which makes sense since the hammer mass is less. If you want a lower inertia action then target a lower FW but be careful.  The main way to achieve lower inertia is lighter hammers or lower AR.  But lower AR means either shorter blow or increased  dip and that comes with its own problems. Also note that it is not the lower FW that is responsible for lower inertia   It is the more advantageous relationship between AR and SW that is responsible  The lower FW is a result of that relationship. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Note: I've made some edits and additions since I first posted this 

David:

It's a big topic so let me see if I can explain.  The downweight (from which we derive the balance weight) represents the minimum force required to actuate the key.  That's typically around 50 grams.  We don't actually play the piano with that low a force, that's just the minimum force required to get the key to go down.  The actual force with which we play the key is much greater generally.  The force required to accelerate the key to the maximum speed (to a achieve a forte) is some 20 times that, let's say 1000 grams.  In reality when we play or analyze the piano we are dealing with rotational dynamics and the force to overcome inertia as we have to accelerate this mass which we call a hammer at the end of a series of levers.  The static measurements (BW) we use don't really capture the fact that we have to accelerate the hammer to some velocity in order to achieve the dynamics that we want from soft to loud.  So when we talk about a "heavy action" what we are really talking about is an action that resists acceleration to a level that is uncomfortable.  That level may vary from pianist to pianist, and, of course we can have insufficient resistance too (a fly away action) so our goal in setting up an action is to determine what level of inertia we want more than just getting some downweight target at any expense.

The primary driver of inertia is the relationship to the leverage we have as a product of the three levers (something we often refer to as the action ratio AR) and the mass we are moving at the end those levers.  There are other contributing factors, the key, the wippen, the lead in the keys, but their contribution is much less than the AR/hammer mass relationship.

So the question is how do we measure that and choose the relationships we want.  Programs like Nick Gravagne's actually calculate the inertia and give us a number which he then translates into a set up that is either acceptable or not acceptable .  The inertia numbers themselves are somewhat meaningless to lay people.  The Stanwood system uses a series of static measurements, key ratio, strike weight, front weight, balance weight, wippen weight, etc, from which that relationship is inferred.  The Fandrich Rhodes system ("Actions to Die For" article PTJ) have their own system and reference numbers, which I don't understand the derivation of exactly, but give an indication of whether that relationship is in the sweet spot.

Most people these days are using some variation on the Stanwood system, probably because it involves simple static measurements.  What can be gleaned when you compare these three systems is that the front weight of the key is an indication of that relationship between the AR and (we'll use Stanwood's terms) the strike weight (SW).  An excessively high front weight to achieve a reasonable balance weight or downweight is an indication that the AR/SW relationship is not a good one: that the AR is not adequate to move the hammer mass indicated by the SW.  With further analysis you find that the FW is a telltale sign through the keyboard as to whether that relationship is maintained.  Stanwood has created a chart of what he calls "Front weight maximums" which, if exceeded, tell you that the relationship between AR and SW is poor.  (I'm not sure how he derived those FW maximums but the exact number are not hard and fast but general guidelines).  You can further analyze that along with the "Actions to Die For" and Gravagne programs to find that there is a real sweet spot where the inertia is adequate that the pianist has some sense of the control of the mass they are moving (they can feel it) but it doesn't fight them too much.  That happens to fall when the front weight is at about 80 - 85% of the front weight maximum at a standard BW of about, let's say 37 - 38 grams, or about 50 grams down weight.

Obviously one can choose a different starting point for the minimum force (measured downweight) as Jim has done when he selected a BW of 47 grams, meaning a downweight at D4 of 58g.  But lets imagine that we are trying to achieve the goal of 80 -85% FW Max and a BW of 37 grams.  That would mean, at D4, that we would be on target if we got D4 to a BW of 37 grams with a FW of about 25g (which is about 85% of the FW maximum according to Stanwood charts).

Let's compare that with Jim's action which is a BW of 47 grams and a FW of 15 grams.  Fifteen grams of FW is about 50% of the FW maximum.  If we want to compare the two actions then we have to compare apples to apples so to change Jim's action from 47 grams BW to 37 grams BW we need to add 10 grams of FW which leaves us then with the exact same numbers as the other action.  (The relationship between FW and BW in the Stanwood system is a 1:1 inverse ratio so one gram added to the FW drops the BW by one gram.).

With the exception of the, probably, one key lead that Jim has removed in his 47g BW action with 15g FW, that action will perform with very similar dynamics to the action that has 37g BW and 25g FW.  The difference being the minimum force required to actuate the key (58g v 50g) and whatever the one key lead contributes to a change in the inertia which isn't very much, measurable but not significant.

In summary, I think actions perform best and inertia falls into the right place when the BW at 37 - 38 grams is achieved with a FW of 80 - 85% of the Stanwood FW maximums at least in the middle of the keyboard.  The SW curve, which can vary, might push the extremes of the keyboard into different territory, I don't think it's that critical there.

Below is a graph of the FW maximums.  My approach in setting up an action is to make sure that from, say, notes 20 - 60 I can achieve my medium BW (say 38 grams) with ~80 - 85% of FW max.  I then smooth the strikeweights from there and can modify the BW if I so choose up or down with small changes in the FW max percentage.  That's a pretty reliable way to get consistent actions.  If you decide later that you actual prefer something different, lower inertia, lower or higher BW, etc.,  then you can use that as a baseline.

Basically the lower the FW at a given BW the lower the inertia which means that the top of the piano always has lower inertia than the bottom which makes sense since the hammer mass is less. If you want a lower inertia action then target a lower FW but be careful.  The main way to achieve lower inertia is lighter hammers or lower AR.  But lower AR means either shorter blow or increased  dip and that comes with its own problems. Also note that it is not the lower FW that is responsible for lower inertia   It is the more advantageous relationship between AR and SW that is responsible  The lower FW is a result of that relationship. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy. 

Note: I've made some edits and additions since I first posted this 

David:

It's a big topic so let me see if I can explain.  The downweight (from which we derive the balance weight) represents the minimum force required to actuate the key.  That's typically around 50 grams.  We don't actually play the piano with that low a force, that's just the minimum force required to get the key to go down.  The actual force with which we play the key is much greater generally.  The force required to accelerate the key to the maximum speed (to a achieve a forte) is some 20 times that, let's say 1000 grams.  In reality when we play or analyze the piano we are dealing with rotational dynamics and the force to overcome inertia as we have to accelerate this mass which we call a hammer at the end of a series of levers.  The static measurements (BW) we use don't really capture the fact that we have to accelerate the hammer to some velocity in order to achieve the dynamics that we want from soft to loud.  So when we talk about a "heavy action" what we are really talking about is an action that resists acceleration to a level that is uncomfortable.  That level may vary from pianist to pianist, and, of course we can have insufficient resistance too (a fly away action) so our goal in setting up an action is to determine what level of inertia we want more than just getting some downweight target at any expense.

The primary driver of inertia is the relationship to the leverage we have as a product of the three levers (something we often refer to as the action ratio AR) and the mass we are moving at the end those levers.  There are other contributing factors, the key, the wippen, the lead in the keys, but their contribution is much less than the AR/hammer mass relationship.

So the question is how do we measure that and choose the relationships we want.  Programs like Nick Gravagne's actually calculate the inertia and give us a number which he then translates into a set up that is either acceptable or not acceptable .  The inertia numbers themselves are somewhat meaningless to lay people.  The Stanwood system uses a series of static measurements, key ratio, strike weight, front weight, balance weight, wippen weight, etc, from which that relationship is inferred.  The Fandrich Rhodes system ("Actions to Die For" article PTJ) have their own system and reference numbers, which I don't understand the derivation of exactly, but give an indication of whether that relationship is in the sweet spot.

Most people these days are using some variation on the Stanwood system, probably because it involves simple static measurements.  What can be gleaned when you compare these three systems is that the front weight of the key is an indication of that relationship between the AR and (we'll use Stanwood's terms) the strike weight (SW).  An excessively high front weight to achieve a reasonable balance weight or downweight is an indication that the AR/SW relationship is not a good one: that the AR is not adequate to move the hammer mass indicated by the SW.  With further analysis you find that the FW is a telltale sign through the keyboard as to whether that relationship is maintained.  Stanwood has created a chart of what he calls "Front weight maximums" which, if exceeded, tell you that the relationship between AR and SW is poor.  (I'm not sure how he derived those FW maximums but the exact number are not hard and fast but general guidelines).  You can further analyze that along with the "Actions to Die For" and Gravagne programs to find that there is a real sweet spot where the inertia is adequate that the pianist has some sense of the control of the mass they are moving (they can feel it) but it doesn't fight them too much.  That happens to fall when the front weight is at about 80 - 85% of the front weight maximum at a standard BW of about, let's say 37 - 38 grams, or about 50 grams down weight.

Obviously one can choose a different starting point for the minimum force (measured downweight) as Jim has done when he selected a BW of 47 grams, meaning a downweight at D4 of 58g.  But lets imagine that we are trying to achieve the goal of 80 -85% FW Max and a BW of 37 grams.  That would mean, at D4, that we would be on target if we got D4 to a BW of 37 grams with a FW of about 25g (which is about 85% of the FW maximum according to Stanwood charts).

Let's compare that with Jim's action which is a BW of 47 grams and a FW of 15 grams.  Fifteen grams of FW is about 50% of the FW maximum.  If we want to compare the two actions then we have to compare apples to apples so to change Jim's action from 47 grams BW to 37 grams BW we need to add 10 grams of FW which leaves us then with the exact same numbers as the other action.  (The relationship between FW and BW in the Stanwood system is a 1:1 inverse ratio so one gram added to the FW drops the BW by one gram.).

With the exception of the, probably, one key lead that Jim has removed in his 47g BW action with 15g FW, that action will perform with very similar dynamics to the action that has 37g BW and 25g FW.  The difference being the minimum force required to actuate the key (58g v 50g) and whatever the one key lead contributes to a change in the inertia which isn't very much, measurable but not significant.

In summary, I think actions perform best and inertia falls into the right place when the BW at 37 - 38 grams is achieved with a FW of 80 - 85% of the Stanwood FW maximums at least in the middle of the keyboard.  The SW curve, which can vary, might push the extremes of the keyboard into different territory, I don't think it's that critical there.

Below is a graph of the FW maximums.  My approach in setting up an action is to make sure that from, say, notes 20 - 60 I can achieve my medium BW (say 38 grams) with ~80 - 85% of FW max.  I then smooth the strikeweights from there and can modify the BW if I so choose up or down with small changes in the FW max percentage.  That's a pretty reliable way to get consistent actions.  If you decide later that you actual prefer something different, lower inertia, lower or higher BW, etc.,  then you can use that as a baseline.

Basically the lower the FW at a given BW the lower the inertia which means that the top of the piano always has lower inertia than the bottom which makes sense since the hammer mass is less. If you want a lower inertia action then target a lower FW but be careful.  The main way to achieve lower inertia is lighter hammers or lower AR.  But lower AR means either shorter blow or increased  dip and that comes with its own problems. Also note that it is not the lower FW that is responsible for lower inertia   It is the more advantageous relationship between AR and SW that is responsible  The lower FW is a result of that relationship. 

Jim 

Curious, what's the front weight at D4?  The BW is less important than the AR/SW relationship which you get a good sense of by comparing the FW and BW. It's the dynamic weight that's more important than the static weight. After all, the static weight only represents the minimum force required to move the key but we don't really ever play the piano with that minimum force-it's always something higher. So if our minimum force is a bit higher but the inertia is still under control the action won't necessarily feel heavy.