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#3185872 01/17/22 06:08 AM
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Hello dear technicians,

Simply, are hammertails supposed(or, designed) to be in check at all volumes(e.g. even when played ppp)?
I want to know how they are meant to behave by factory standard, in realty or idealy.

For years I struggled dealing with my piano which had very bouncy keys (because the hammers
rarely got checked, even at F(orte), so they bounce on rep levers and you feel the vibration
in the key you know).

My tech then could not fix the problem but when another tech replaced the key bushings (front and balance)
and wippen cushions, the problem was almost completely gone.

Now I own another piano( yamaha s400B) and am about to have it regulated, i want to know to what extent
can I be demanding about backchecking.
Is it realistic to demand that hammers get in check as long as the keys are depressed fully to the bottom
even played ppp?

Thanks in advance.


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hairline #3185885 01/17/22 07:21 AM
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hairline #3187460 01/21/22 10:47 PM
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There are so many things that can influence checking, including condition/adjustment of the backchecks, shape/radius/condition of the hammer tails, wippen spring strength, hammer weight, repetition center pin friction, hammer flange friction, and even drop. Good checking is a balancing act.

I admit I often have trouble with bass/low tenor hammer catching. The only thing worse is getting perfect damper timing.

In your case, I think it will depend on your technician. It take some experience with grand regulation to master checking.

Maybe some other techs can chime in, but I'm not clear why replacing the wippen cushions should help. I guess if the keys are bouncing around with very loose bushings, that could possibly affect checking, but I'm not really sure.

hairline #3187465 01/21/22 11:22 PM
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Greetings,
There are a number of things that can prevent checking from being trustworthy. However, it is important for repetition speed that the hammer check, since it is by checking that the repetition spring is "loaded". The spring is responsible for accelerating the key's return, which must happen for the jack to reset and a key that is unchecked is much slower to rise than one that is, (you can see this by slowly pressing a natural key down so the hammer escapes but is not held in check, then play an adjacent natural firmly enough so that it is held in check. When both keys are simultaneously released, the checked key will return much faster).

The radius of the hammer tail and the angle of approach of the back check are critical, as is the friction to be found between them. I radius my hammers at 1/2 the distance from the center pin to the hammer's centerline, about a 65 mm radius. The back check, at rest, is approx. 5 degrees away from parallel to the hammer's centerline.
Excessive spring strength will place inordinate demands on the checking, and is not only useless resistance at escapement, it also will require a greater drop distance to prevent double striking the string under certain play.
The less dip there is for a given blow, the less distance the backcheck covers, and without enough aftertouch, there will be too much distance between the tail and the back check when the key reaches the bottom of its travel.

Repetition speed is determined by two things, the speed of the key's return and the distance it must travel . The speed is determined by the spring and the inertia of the key. Once the spring will lift the hammer from check as fast as possible without the knuckle bouncing off the mortise, additional strength is of little use and considerable expense to touch sensitivity. The upwards distance the key must travel to allow the jack to reset under the knuckle is dependent on the height of checking, so higher checking is conducive to faster repetition. For this reason, it is usually beneficial to have the checking no more than 40% of the blow distance away from the string. That is a general consideration, for particular demands on repetition speed, a stronger spring may be worth the extra resistance.
Compliance in the action, primarily the capstan felt, also affects checking, in that a great deal of compliance will allow the key to reach the front punching before the hammer begins to move,(Anderson/Askenfelt "Five Lectures"). This condition will require the back check to be farther away from the key to prevent dragging between it and the tail on the key's (eventual) rise. which will result in a lower check height.
In order to check on very soft blows, when the hammer's rebound speed is quite slow and the key perhaps not fully depressed, the spring must not be overly strong, the hammer tail not polished, the check leather in good condition, and the relative positions of both check and tail be optimum.
Regards,

hairline #3187467 01/21/22 11:46 PM
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Some excellent answers above but they are lacking one pivotal principle.

The higher that mass of the hammer, the slower it rebounds from the string. In soft playing, too heavy hammers barely fall from the string with any force at all and thus it refuses the check.

I make actions with very low mass hammers and very high leverage. They check reliably with soft playing. This affords a wonderful evenness and control to the soft playing experience.

Lighter hammers also last way longer. The vast majority of hammers made since WW1 are way over the weight limits that allow best function. Hammers were much lighter on modern pianos in the 19th and early 20th century.


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Ed Foote #3187469 01/21/22 11:58 PM
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Originally Posted by Ed Foote
Greetings,
There are a number of things that can prevent checking from being trustworthy. However, it is important for repetition speed that the hammer check, since it is by checking that the repetition spring is "loaded". The spring is responsible for accelerating the key's return, which must happen for the jack to reset and a key that is unchecked is much slower to rise than one that is, (you can see this by slowly pressing a natural key down so the hammer escapes but is not held in check, then play an adjacent natural firmly enough so that it is held in check. When both keys are simultaneously released, the checked key will return much faster).

The radius of the hammer tail and the angle of approach of the back check are critical, as is the friction to be found between them. I radius my hammers at 1/2 the distance from the center pin to the hammer's centerline, about a 65 mm radius. The back check, at rest, is approx. 5 degrees away from parallel to the hammer's centerline.
Excessive spring strength will place inordinate demands on the checking, and is not only useless resistance at escapement, it also will require a greater drop distance to prevent double striking the string under certain play.
The less dip there is for a given blow, the less distance the backcheck covers, and without enough aftertouch, there will be too much distance between the tail and the back check when the key reaches the bottom of its travel.

Repetition speed is determined by two things, the speed of the key's return and the distance it must travel . The speed is determined by the spring and the inertia of the key. Once the spring will lift the hammer from check as fast as possible without the knuckle bouncing off the mortise, additional strength is of little use and considerable expense to touch sensitivity. The upwards distance the key must travel to allow the jack to reset under the knuckle is dependent on the height of checking, so higher checking is conducive to faster repetition. For this reason, it is usually beneficial to have the checking no more than 40% of the blow distance away from the string. That is a general consideration, for particular demands on repetition speed, a stronger spring may be worth the extra resistance.
Compliance in the action, primarily the capstan felt, also affects checking, in that a great deal of compliance will allow the key to reach the front punching before the hammer begins to move,(Anderson/Askenfelt "Five Lectures"). This condition will require the back check to be farther away from the key to prevent dragging between it and the tail on the key's (eventual) rise. which will result in a lower check height.
In order to check on very soft blows, when the hammer's rebound speed is quite slow and the key perhaps not fully depressed, the spring must not be overly strong, the hammer tail not polished, the check leather in good condition, and the relative positions of both check and tail be optimum.
Regards,

Excellent explanation!

I actually ALWAYS loved the challenge of getting checking as close to the strings as possible, when successful it was like notes dancing off your fingertips.

My three favorite parlour tricks were very slight adjustments to the backcheck's angle, custom roughing up the tails with a razor, and fine adjusting rep spring strength.

Goal was zero bobble on pppp in treble, perfect catching in bass on ffff.

Of course without getting the jacks forward to just before the point of failure on hard blows the hill's steeper than it needs to be.

BTW, all 85 hammer tails on my 1859 Steinway are carbon fiber wafers, custom cut to each hammer, and affixed with superglue and epoxy, and fine adjusted with a diamond grinder. They catch on genuine new Steinway grand backchecks, modified for the project, so I went pretty far down the backcheck rabbit hole on simple escapement actions.

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AOS,

Would you mind posting a picture of your hammer tails?

Peter Grey Piano Doctor


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P W Grey #3187634 01/22/22 03:12 PM
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Originally Posted by P W Grey
AOS,

Would you mind posting a picture of your hammer tails?

Peter Grey Piano Doctor

Be happy to! smile

None on my computer so they'll be fresh pics.

Ya wanna see something REALLY nuts though?

The damper system has had the amount of damper felts *tripled*.

That also hinged on a lot of custom carbon work.

Pics o' that too.

By the way, like to make a free uncompensated plug for my carbon supplier, DragonPlate.

https://dragonplate.com/

They're selection is amazing and their engineering dept is very helpful answering questions.

P W Grey #3188043 01/23/22 08:28 PM
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Originally Posted by P W Grey
AOS,

Would you mind posting a picture of your hammer tails?

Peter Grey Piano Doctor

Ha, getting to them to take the photos.

I do NOT just "pull the action". It's far too old to do anything but be as careful as possible. I have a collapsible table exactly the height of the action onto which I slide the action out in slow motion with the awareness of a bomb disposal tech.

Problem today is that table is piled high with several hundred objects that need to go elsewhere like where they belong.

As soon as I have a table to slide the action out onto I'll do some photography.

In the meantime, an octave fifth effect solo noodling around micro-piece. Dampers removed so you can see it. The damper lifters (lower left corner) are also my invention, carbon rods with a steel ball bearing epoxied to the top (that attaches magnetically to magnets embedded in the bottom of the damper levers), with a buna-n rubber ball on the rod for regulating dampers.



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