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Joined: May 2021
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alabana Offline OP
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Hello everyone!

I have a bit of a problem. I got the hammers on my piano replaced because they were old. Now, this is a Korean made young Chang U121 so by no means a high end instrument. With the replacement service came a total regulation and calibration of the action. The weight of the Keys before this service was messed up, a lot of keys had a weight of over 100g. Now, after the service, it is a lot better but I feel like I didn't get what I was supposed to get, because:

While all keys are lighter now, there is a lot of variance. For example: C3: 67g, D3: 46g, E3: 55g. It varies across the keybed and it's never really even. Sometimes, playing an arpeggio feels like I "fall into" one of the keys because the other ones are much heavier. Also, the black Keys are about 10g heavier on average than the white keys

My questions are: what variance is acceptable between the keys?

Is a difference between the black and white keys normal?

I measures the key weight while the damper pedal was pressed and measured the weight that was necessary for the key to sink to the let off without making a sound. I used a home-made device consisting of a M12 screw weighing 40g and washers that weight 3g each and placed it as far out as I could. Sadly, I don't have anything more accurate but the difference is apparent nonetheless.

Thank you for your time and answers!

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I believe this is an upright, correct?

If so, the jack springs may have varying strengths and or there is uneven weights in the keys.


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alabana Offline OP
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Yes, it is an upright. Since I have the original keys wouldn't the weights be still balanced out of the factory? I noticed though, when the action was taken out, that some keys moved freely and others got stuck when pushed down. The technician said that was normal though...

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Thank you for the video! That is some insane precision! I feel like I could maybe do this myself if need be. Would be scary though. Is this process usually included with an action regulation after hammer replacement? The technician told me that after having the service done the piano would be in great condition again. I feel like it is not in great condition without this process.

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Because you know how to measure down weight (DW), the next thing to do is to measure up weight (UW). As you did previously, keep the damper pedal depressed. Start with each key fully depressed and find out how much weight it takes for the key to slowly rise. Record the value for each key. Now you can calculate the friction for each key, which is just (DW - UP)/2. In so doing you can determine if the variations you are seeing are due to inconsistent friction. That's always the first thing to check when determining the cause for this type of problem, IMO.

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alabana Offline OP
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Thank you so much, that is a really great tip! I will do that as soon as I have a chance!

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alabana Offline OP
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So I have measured the upweight and calculated the friction for 2 full octaves (C3 to C5). I figured that will give me the idea without having to do the whole keybed. Here are the results:

KEY DW UP Friction

C3 67 27 20
C#3 67 30 18,5
D3 46 23 11,5
D#3 55 40 7,5
E3 55 33 11
F3 58 39 9,5
F#3 61 40 10,5
G3 55 33 11
G#3 61 33 14
A3 49 33 8
A#3 61 43 9
B3 55 39 8
C4 49 36 6,5
C#4 61 39 11
D4 58 30 14
D#4 61 36 12,5
E4 52 36 8
F4 61 36 12,5
F#4 58 43 7,5
G4 58 36 11
G#4 61 40 10,5
A4 64 36 14
A#4 58 36 11
B4 52 39 6,5
C5 58 36 11

So the friction varies between 6.5 and 20. I actually did do the bottom two notes as well and the B1 had a friction of 29g. I think it's pretty clear that the keys with lower down weights also tend to have lower friction. There is some variance but keep in mind that my weights were not calibrated and the 3g step is far from perfect.

I guess that means though that the action has not been regulated well enought or they didn't replace enough axis's in their shop?

Last edited by alabana; 05/15/21 04:16 PM. Reason: I tried to make the table more readable but I couldn't figure out how so I just made the friction values bold
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Friction can arise from a number of sources. The excess friction could be in the fit of the cloth key bushings to the key pins, the tightness of the pin in the balance hole in the bottom of the center of the key, the interface between the capstan at the back of the key and the cloth surface on the bottom of the wippen, or in any of the three center pins -- wippen, jack and hammer flanges. Of the three center pins, the one for the hammer flange is the most likely culprit.


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Yep you have friction problem. Were the keys rebushed?


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alabana Offline OP
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No, the keys are in their original state. The technician only took the action with him to the shop and not the keys. He said they would regulate the action in my home after the hammer replacement and upkeep work on the action. He said that they replaced some of the pins but not all of them because some were still good.

He also said that I need to play for a few weeks now to break in the hammers a bit before he can do a final intonation. I'm having him come back this week to address some of my concerns. I just want to be prepared and at least know somewhat what I'm talking about. He didn't say they were going to rebush the keys but he did say I wouldn't need any major work done for the next 20 years after the service.

So I don't know if I it would be reasonable of me to request for him to deal with the friction at no extra cost (the total bill was about 1600$).

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Don't know how an action can be regulated if it has uneven and/or problematic friction. Your tech should have a balance rail pin hole reamer and easer as well as key easing pliers. I suspect the balance pin hole at the bottom of the key is making trouble.


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Ok. He will be here Wednesday so I'll ask him about everything and I'll see what he says. I will post an update after.


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