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How do I fix double striking in an upright?

Posted By: ppsantos

How do I fix double striking in an upright? - 08/03/07 10:20 AM

I had my upright piano (made in China) tuned 16 days ago, and one double striking key was fixed. Today I noticed another key double striking when played pp. I read that this is not uncommon problem in upright pianos. How do I fix the double striking key , even if I have no background in piano action? Or should I call the piano technician to fix it, and possibly pay again?
Posted By: BDB

Re: How do I fix double striking in an upright? - 08/03/07 10:58 AM

There is probably nothing you can do to fix it. If you can live with it, wait until the next time it is tuned. Keep a record of double-striking notes for the tech.
Posted By: Keith Roberts

Re: How do I fix double striking in an upright? - 08/03/07 06:13 PM

You have a common problem. It is caused by felts packing and settling in with playing. It is problem with the whole piano not just one note. The action adjustments need to be brought back into the parameters of an action.
More than likely the keydip has gotten shallow or some lost motion has developed so on pp blows it bobbles. maybe both.

If I have to keep going back many times for the same problem before I solve it, I don't want to know how many notes it was. How embarrassing.
Posted By: Gene Nelson

Re: How do I fix double striking in an upright? - 08/03/07 07:27 PM

I always like to advise clients with uprights that their playing technique can cause the double strike on pp or ppp playing simply because on the upright action you must completely bottom out the key against the front rail punching when playing. It is tempting to not do this when playing softly.
If the double strike keys appear random then check your technique.
Posted By: Bill Bremmer RPT

Re: How do I fix double striking in an upright? - 08/04/07 09:54 PM

Gene is right about this. Any technician can "fake" double striking in a piano by knowing just when to stop pressing the key. While it is entirely possible that some action parameters have fallen short, it is also equally possible that the pianist feels the point of escapement (also called "let-off") of the action and when attempting to play very softly and stops pressing the key at that point. The hammer then rebounds on top of the jack. Americans call this "hammer bobbling", the French Canadians call it "dancing".

One thing you, as the piano owner can do is to lift off the front panel to observe how the piano action (the mechanism) works. Get a flashlight and with the left hand (or have someone else hold the light) and observe how the mechanism of one of the ends of a section works, where you can get a good side view. Play the key with normal force (mf). You will see how the piece called the "jack" pushes the hammer but just before the hammer reaches the string, the jack will escape backwards to allow the hammer to strike the string freely and then be caught (technicians call the catching action to "check") by the piece called the "back check".

Then, press the key very slowly and gently, as if trying to play "ppp" and stop just at the point of escapement. The hammer will probably rebound and double strike as you have described. If you then play the key very softly again but deliberately press it all the way through its range of motion, it should play normally. Now, move to a key that you were experiencing the problem with. If you play very softly but are sure you press the key through its entire motion and the hammer still rebounds and double strikes, it does indicate a regulation problem. If not, it indicates that when attempting to play very softly, you are also not playing the key through its entire range of motion.

The most common cause for a regulation problem in such a new piano would be what technicians call "lost motion". This develops primarily because the jack itself has compacted the material of the hammer butt against which it pushes. This material is soft and compresses easily. There is other material which can compress as well, the back rail cloth against which the key rests and the balance rail material upon which the key lies. But it the case of the last two, the level of the key would appear either too high or too low respectively. These latter two causes are less likely at this point.

To test for the lost motion problem, put your finger on the key and press very gently and watch to see if the backcheck moves slightly before the hammer but is engaged. Watch the piece directly in front of it called the "catcher". If the two pieces do not move simultaneously, there is lost motion and you will need a technician to adjust the action to remedy it.

Manufacturers of vertical pianos most often will set the distance from the hammer to the string as the hammer is at rest called the "blow distance" slightly short of the ideal specification when the piano is new, specifically to avoid the problem you describe. Lost motion sets in very easily and quickly on new pianos. The slightly short blow distance causes the jack to escape and move back further than it really needs to when the piano is new but avoids the problem you describe. The jack escapes early in the key movement and the player doesn't notice or feel that movement. So, even if the player doesn't press the key entirely through its range of motion, the hammer will not rebound or double strike.

It is also possible that the escapement adjustment for the keys you have a problem with has been set a little too close to the string. This would also cause double striking when the player's technique is not really at fault. This kind of problem would only involve a very quick and easy adjustment to the problem keys. If lost motion is the problem, it also can be remedied fairly quickly. If it is determined that all of the hammers are near the limit at which they would rebound upon very soft playing, even with full range of key motion, the hammer rest rail needs to be set just slightly higher as with a thin shim of cloth being glued to its rest pads, then the resultant lost motion needs to be adjusted for each key. The latter is a very commonly needed adjustment in a new vertical piano.
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