Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Reblitz vs Igrec on Backcheck and Rep Sprin regulation specs

On backcheck checking distance Reblitz at p. 187:

Each hammer should check exactly 5/8" (16mm.) from the strings (rack).

Igrec at p. 174:

Typically, backchecking is adjusted between 1/2 and 5/8 (12 to 15 mm.) from the strings.

I'm curious: why does Reblitz tell say "exactly" 16 mm.? I'm guessing that Igrec's view is closer to the "modern" and more "nuanced" approach to regulating the backcheck?

On repetition spring tension:

Reblitz at p. 188:

Play each key so the hammer checks. Then let the key come up just a little, and immediately push it all the way down again, releasing the hammer from the backcheck and permitting the hammer to rise slowly but positively to the drop position .....

Igrec at p. 175:

the hammer should swing up in a decisive, quick, but not jerky motion,....

There seems to be a real discrepancy here. Which is it? "Decisive and quick" or "slowly but positively"?

I've often said that if you ask 10 piano technicians a question, you'll get at least 12 conflicting answers. Reblitz and Igrec are simply reflective of the fact that this is very much "signature" work. There is plenty of room for personal approaches and preferences which will still fall within a range that would be regarded as generally acceptable.

Read any of the threads about tuning on this forum to confirm just how varied opinions and approaches can be. The same variety of opinions exists with regard to regulation - though the arguments seldom seem to become as heated.

Igrec's book generally contains more updated information concerning specs for new parts, and regulation details that have been discovered since the time of the Reblitz publication.

Checking distance between 12 and 15mm is more correct. There is a range depending on the parts, wear and what choices the action regulator has decided upon for performance.

Hammer rise from the check position is ideally a firm, continuous rise.. but this is dependent upon hammer/rep centers being at the right friction, and spring slots being cleaned and re-lubricated if present.

You will get different answers from every tech, but some are more inclusive and correct than others. Sometimes, both people are right, and they are describing the same nuance from different directions. In the end, a spec is only a number derived from a deeper understanding of the engineering and operational parameters involved. A spec alone says nothing.

Checking is not so sensitive a parameter.. how the checking engages is more critical. A firm rise is critical because a wide range of dynamics/timing can create a collapse of the rep mechanism which is very frustrating to musicians.

Higher checking generally results in faster repetition, but not always. Higher checking also results in a firmer-feeling action, which is not desirable to many.

Checking angle and installation height, hammer bore and tail curvature/length are the parameters linked to ideal checking height. There is a point delineated by the curvature of the hammer tail and arcs involved that can be found accurately, by feel.

Very well written!!! +1

What Gerry said - it's indeed a matter of taste. Regulation will vary depending on the piano and preferences of the pianist.

I like a light and responsive touch on my piano, so I prefer quite less than what is mentioned for backchecking and weak springs (adjusted to rise slowly/gently). Of course, another pianist might prefer the opposite.

If it's your own piano, experiment and see for yourself what you prefer. Set (or ask your technician to set) one octave a certain way, another differently, etc. Then practice similar patterns on them for a while. You will feel the difference while playing.

My current rule of thumb is to rough in the backchecks at about 12 mm from the string, and then, to go back and forth between a spring tension that isn't so much as to permit the hammer to escape from check or to bobble against the string on light blows, but is strong enough to facilitate fast trills, etc., at pp.

I find myself adjusting, alternatively, the drop, the spring tension, and the check distance. It's a balancing act that is taking me a huge amount of time yanking the action, adjusting, and pushing the action back in.

C'est la vie.

I have a good tech whom I'm calling in when all's done.

I find the comments here very helpful, as always.

You're right about the backchecks. They should be note-to-note consistent but can vary from piano to piano depending on other factors and even can vary from one section to another on the same piano.

Regarding repetition lever spring tension:
Each is an attempt to use words to describe a complex physical event. Those words are useful to guide someone into the regulating process. They are not something to be quibbled about at arms length. To me, they describe different ends of what is a tolerance, not a point.

I'm not sure if you have set the repetition strength or not. For someone that hasn't, these statements will never make sense until you do it. It's kinda like having an internet debate over the meaning of "allegro ma non tropo" without ever having listened to music that represents that marking.

When one begins to master tone regulation-it becomes obvious that each action has its own set, (or maybe range is a better term) of regulation specifications. You want control over the action from start of stroke to leaving the key. And all of the regulation dimensions must be derived from evaluation of the overall performance of the action in all types of dynamics used and all types of repeated note or groups of note combinations.

You finger wants to feel what acceleration you are imparting into the hammer and feel the start and completion of escapement. Your finger also wants to feel where in the released keystroke the hammer is available again for striking. As well the damper must be cleared and returned to the strings at the proper places in the keystroke.

That said-how strong the repetition springs can be, is very related to the inertia of the hammer, the friction of the hammer center and the geometry of the hammer tail/back-check arcs of motion and key dip.

Long checking distance and weak repetition springs are a recipe for a very poorly repeating action.

Also the escapement must have enough distance from the string that close checking and strong springs don't start to create double-strikes with soft playing.

Heavy hammers require stronger springs but this combination very quickly makes for an uneven-and-almost-stopped-keystroke-before-escapement-is-complete-feel during soft playing.

Hope this helps-but there is no simple cookie-cutter recipe for universal action regulation.

Probably the most difficulty technicians have mastering regulation is understanding how the piano is played first.