Bobbling hammers

[Jason Kanter]

Please advise, group. This Kohler & Campbell SKV-48S vertical has me stumped. In the center section, on soft blows, the hammers bobble (bounce off the jack head and strike the string twice). I have reduced blow to between 1 3/4 and 1 5/8, slightly increased letoff to about 1/8, allowed a teeny bit of lost motion, and increased dip/aftertouch (though the bobbling happens before letoff and long before the key bottoms out) -- and although it is better, it is still happening. But it's not a problem in the bass or treble. 

What am I missing?

Thanks in advance

Jason

("Registered Craftsman" in 1971, lapsed membership in the 80s, now an Associate)

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jason's cell 425 830 1561

[tnr...@aol.com]

Jason

 

The reason the hammer is bobbling is because the jack is not escaping. Put all the adjustments back to where they should be, but then keep taking out front rail punching, a little at a time, until the hammer checks like it is supposed to be. Having a little more dip is more important than any of the other adjustments.

 

Happy New Year

 

Wim

[David Renaud]

Jason

   When the key is bottomed out, where is the jack relative to the hammer butt?

   Is the jack still brushing the hammer butt, despite the adjustments made as of yet?

   How much space between the hammer butt and the jack when fully engaged...paper thin, 

1/16th, 1/8th.......?

    The regulation measurements can be  "correct" and still not work if the geometry is "odd"

I recall an Asian 7 foot grand with all Renner parts that nobody could regulate. The technician 

Had 7/16 of dip and 1/1/2 inch of blow and it still was not happening. Upon measuring the 

action ratio, it was 4.2 , 11mm of dip would only yield 46 mm of hammer rise, barely making the

Let off button. I also can think of the opposite extreme, a very old chickering with an action ration of 7.6. Normal conservative dip and blow, and the jacks were still buried, stressed, and breaking.

    So use the actual observed gap between the jack and hammer butt to judge if your choices of dip and blow distance and working out for this particular piano.....

              Hope that helps....

                                               Dave Renaud 

                              

    

Sent from my iPad

[Paul Milkie]

Follow Wims advice or shim balance rail with one of your business cards.

[Isaac OLEG]

Last option not very often but happens on Silent type verticals when let off have been left too close from the strings for a long time.

A nick install in the butt leathet and hammer is propulsed to the strings before real let off, then rebound while let off begin or before, depending..
Double strike at soft regime guaranteed.

[David Boyce]

On 25/12/2013 21:51, Paul Milkie wrote:
> I have reduced blow to between 1 3/4 and 1 5/8, slightly increased
> letoff to about 1/8, allowed a teeny bit of lost motion, and increased
> dip/aftertouch (though the bobbling happens before letoff and long
> before the key bottoms out) -- and although it is better, it is still
> happening.

I'm a bit puzzled by how the hammer can strike the string more than once
(bobbling) BEFORE letoff?

On a nice new Kawai just over a year ago a client, a learner who had
recently taken up lessons, complained about bobbling on soft tentative
playing. I was easily able to see it myself as I sometimes play rather
tentatively. This was a nice Milennium 3 Kawai action. I had Don
Mannino's regulation notes with me, from his upright regulation class at
MARC 2011, and cautiously adjusted setoff etc. Without much success.
What immediately made the difference, however, was just slightly bending
the bridle tape wires back, to make the bridle tapes a little more
taut. The affected notes played cleanly then.

Best regards,

David.

[Tony Caught]

Key dip. Check your key dip in the middle and compare with either end. Often I lift the balance rail up in the middle with a few pieces of paper to solve the problem. Tony

[Paul McCloud]

Hi, Jason:
Try to see if the damper springs are extra strong. If so, weaken them a bit. If they are too strong, unless the pianist is using a forceful blow, the damper spring will slow down the velocity of the key, and the backcheck won't stop the hammer from bobbling. Many of the pianos coming out of China have this problem with bobbling hammers, and the damper spring tension seems to be the culprit. Check it out.
Good luck.
(Merry Christmas, too, BTW!)
Paul McCloud
San Diego

----- Original Message -----
From: "Jason Kanter" <jka...@rollingball.com>

[Arthur]

Check key level. Older piano center could be low. Making dip shallow.

Sent from my iPhone

[Keith McGavern]

On Wednesday, December 25, 2013 2:48:09 PM UTC-6, Jason Kanter wrote:

Please advise, group. … What am I missing? …

Jason,
Do they bobble with the sustain pedal engaged?
Keith

[Isaac OLEG]

Sure, anyway what happen is an incorrect checcking

So the best way to check action functions is to bend the back check wire out of the way.

Happy Christmas

[Isaac OLEG]

That is how I chek for any repetition problem. Bend the backheck wire so no checking happens.

Then the final position of the jack is easily checked, as proposed above.

Hint : the hammer position when retained by the jack gives a clue about the space between the butt and the jack.

I now my post are BS or considered as, but think about that proedure, if you do not know it yet.

In fact this is basically how I find the hammer travel distance for a given action.

[Geoff Sykes]

Tentative playing is a common culprit of bobbling hammers. In playing tentatively it is quite easy to unconsciously become aware of the exact moment when the jack hits the letoff adjustment button, and you hesitate just ever so briefly. Regardless of how well the piano is regulated if one can't overcome that brief moment and cleanly move the key through it's stroke you will get bobbling hammers. What has happened is you have unintentionally, and very briefly, stopped the movement of the key while the hammer is already at close to full velocity. The key stops. The hammer keeps moving. It strikes the string prematurely and then bounces off the jack as you complete your keystroke, hitting the string a second time. 

Once you, as a technician, become aware of this you can easily demonstrate it to a tentatively playing customer as something that MAY be happening and which they need to become aware of and NOT do it. Works on both uprights and grands. 

[Jason Kanter]

I've had a nice set of responses, and will respond when I have had a chance to check the piano again, probably in the next few days. Thank you all.

Jason

[David Kroenlein]

sometimes the damper spring is overly strong, and on a soft blow wil prevent the hammer to freely hit the string

[Jurgen G]

I think Geoff is onto something that is important.  I will take it a step further:
On many pianos, fairly thick and soft front rail punchings compound the problem of bobbling hammers.

The actual key dip is measured with a fair bit of force on the FR punching, about 6 - 9 ounces.  This is much less than tentative player exerts in play.  A soft FR punching will compress less in play, resulting in an actual reduced key dip (and after touch!) for the player, causing the hammer to bobble.

The remedy in such a case is to go with a firm FR punching such as the Crescendo Punchings.

By all means, check the regulation including dip and after touch, damper timing and spring strength etc.  But don't discount the physical characteristics of the FR punching.

Jurgen Goering

[Isaac OLEG]

Any vertical piano player need to learn to play with sufficient speed, or to really bottom the keys.

There is a way to regulate vertical pianos to emulate grand touch.

The front punching play a role but relate to the springiness of the back check wire too.

What is funny is that obtaining that precise after touch that emulates correctly a grand touch, is obtained with unsuspected tips and tricks.

[David Skolnik]

Perhaps as an OnT (as opposed to OT) tangent from Isaac''s last post, consider the role that string plane, or, more precisely, shank orientation, plays in upright design and regulation.  The upright action design is affected, to a much greater degree, by variation in orientation to true perpendicular than a grand action.  If, for example, the 'off-perp' anomaly causes the hammer shank to attain or exceed 90 degrees, the hammer return spring will be much less effective in achieving what is accomplished by gravity, in a grand action, most especially in the case of soft, or tentative playing.  The very need to increase the tension of this spring in such a case would exacerbate the problem, at the lower dynamics.

Another possible contributor could be hammer pinning that is excessively loose, eliminating the 'drag' that could help player's control in soft playing.

And, last, in attempting to emulate the characteristics of grand touch - hammer rise - does anyone still have, in their stable of clients, a working Mason & Hamlin upright action with auxiliary jack return springs?  I saw these on a 52" upright, but other problems with the action prevented me from determining how effective they were.

David Skolnik
Hastings on Hudson, NY

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[David Skolnik]

Hi Jurgen -
I think this confuses the issue a bit beyond where it needs to go, even if the fundamental problem of accurately quantifying key dip is correct.  In other words,  while many things can contribute to the bobbling problem, I think that it exists apart from the mechanics of how key dip is established (by the technician) and how it's perceived, by the player.  The subject of how we do this has probably been discussed in the past, but maybe should be revisited, in the new year.
Best Wishes -

David Skolnik
Hastings on Hudson, NY

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[Isaac OLEG]

Hi David, I find it relatively rare that hammers are so short the CG of the hammer assembly is above the flange center.

Yet in the butt, the center location is slightly front of the shank center.

With the hammer touching the strings, the gravity center is still back from the hammer shank usually, abot a shank thickness.

I agree that too strong return spring can be a hassle for repetition.

About control on hammer acceleration, I feel it is limited with the butt shape.
There is some compression on the butt cushion that generates some added resistance, while at the same time the shank, (and possibly the action rail) flex a bit.

So the best we can get is some energy accumulation/release. Then precise after touch can provide a bit of synchronicity between tone production and checking, at strongest modes of playing.

The most annoying effect to find good regulation distances is checking.
Unless a weighted key is jauge is used, the pressure on the front punching will vary between basses and treble, between sharps and white notes.

So it is much easier and more precise to find distances without checking.
This also allow to take in account the larger checking distance in basses vs treble.

This is just a factory method, so usually for a new action, but it is as efficient on a moderately used one.

Not easy to get the minimum jack/butt distance when the hammer is retained by the checking.

[Isaac OLEG]

Also the springiness of the vertical punching is helping key return, but only when the compression of the punching is related to checking.

I know no better way to have a good touch on verticals. Of course with good damper timing, not excessively strong damper Springs, etc.