Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Changing an upright action ratio

Shallow key dip along with hammers too far away from the strings will fell very heavy and slow.

Hello, would anyone be able to suggest the ways of lowering the action ratio on an upright?

I was just reading another thread, in which somebody mentioned how a large blow distance with shallow key dip will feel heavy. I do agree with this, but what else can you do if the action ratio is so high that changing either of those two will result in too much jack movement?

I know the capstan can be moved,or bending the pilots, but what are the other options?-For example, changing hammer butts,whippens etc?-Can changing centre pin heights/distances alter the ratio?-In what way?-(assuming the change is part of an action redesign).

Wouldn't correcting the regulation be better than changing the action ratio?

Do you have a particular piano in mind?

Thanks Del and Isaac, i will experiment with that at some point. I don't tend to see much variation in cushion thickness on new parts though, have you ever had to modify new parts?

I'm thinking about if an action regulates with excessive blow distance combined with dip under 10mm, the action ratio is too high.

As it happens the Ibach in my signature below fits your description: blow distance 49mm, dip 9.4mm, overall action ratio to let-off 5.5.

The Ibach action does not seem particularly heavy but it's certainly heavier than the Schiedmayer: overall action ratio 4.0.

The problem with that low action ratio was the key dip came out at over 11mm when I followed Reblitz. Reducing key dip to 10.5mm and restricting jack movement made the action feel much more responsive.

Most modern pianos have some version of the Erard/Herz action. Most of these are patterned rather directly from the design Steinway adapted something like 150 years ago...

So…the basic action functions and geometry are more-or-less fixed. What are variable are things like hammer mass and the overall lever ratio. Years back—as in when I started out in this business—the de facto standard hammer travel was approximately 45 mm (1 ¾”) and key travel was approximately 9.5 mm (0.375”). Even then, of course, Steinway was a bit different with a published standard key travel distance of 9.9 to 10.0 mm (approximately 0.390”). With pianos like the Steinway, of course, this could vary considerably depending on where the action stack was located and in the end key travel would be determined by how much travel was required to ensure adequate key aftertouch.

As piano hammers became heavier over the years these specifications became some unworkable. To keep key downweight within reason increasing amounts of lead weight would have to be added to the front of the keys. This looks fine for static measurements but the amount of inertia makes fortissimo and fast repetition difficult. The answer was to increase (numerically) the overall action ratio (OAR). For a given hammer mass an action with on OAR of 5.5 (a hammer travel of 5.5 mm for every 1.0 mm of key travel) will have a lighter feel than one with an OAR of 6.0 (a hammer travel of 6.0 mm for every 1.0 mm of key travel). In general manufacturers have kept the hammer travel pretty much standard choosing instead to increase the key travel. This has, I think, pretty much reached its limits now with some actions requiring as much as 11.0 mm of key travel to function properly.

Simplistically, the variables the action designer has to work with are hammer mass, hammer travel and key travel. Still very simplistically, the there are several ways to go about achieving a given OAR; the hammershank length can be varied, hammershank knuckle can be moved closer to or further away from the action center; the contact point between the key capstan and the capstan block on the wippen can be moved and the key balance point can be moved. (Key length is mostly a function of piano length.) If a relatively heavy hammer is selected the OAR will need to be numerically lower and if a relatively lighter hammer is selected a numerically higher OAR can be used. For a given hammer travel and key touchweight the action with the heavier hammer will require more key travel while the action with the lighter hammer can get by with less key travel.

Ian, I was a little confused by the OAR of 4, regulating with 45 blow and 10.5 dip, i would have expected more like the 40 blow and deeper dip ...