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Hello, technicians. Wonder if you can help with something.

My 8 year old Hobart M Cable upright is housed in my basement. Humidity is typically very low (@30%). Middle C# has been sticking intermittently. Every other key works fine.

My sump pump failed on Friday. The carpet underneath the piano got very wet but there wasn't standing water. Humidity shot up to 70% or higher. I moved the piano to a dry area (about 6' away) and am trying to dry the carpet out. Meanwhile, C# is working fine.

I have two questions:

1) Could the normally low humidity level cause the key to stick? How do I deal with a situation like that?

2) Is this sudden swing in humidity going to cause any problems? What kind, and how are they dealt with? Should I move my piano somewhere else?

Thanks in advance for your input!

-Matt

Give some more detail of how the key is "sticking". Does it stay down when pressed? Does it come back partially and stop? If you push the keys beside it away from it, does it come loose? Sometimes the action parts farther up the line can cause the key not to come back up also. Most of the time the key slip is likely interfering with the front of the key. Do you see the front of the key touching the wood in front of it (keyslip)as you press it down, or is there a gap? It could also have a swelled bushing but typically this occurs at higher humidities, not lower ones.

The key stays all the way down about half the time, and pops up normally the rest of the time. I've fiddled with adjacent keys to no avail. There is a uniform gap between the adjacent white keys and the key slip, and there is a gap between the offending key (middle C#) and the adjacent white keys.

I removed the top door and tried to find any difference between the area in question and any other area of the piano in the mechanisms and can't see anything.

Humidity level has risen to 80% and the key is working fine right now. I'm puzzled.

Hello, yes keys get tighter with dryness, If you did not leave for long your piano in the moisture no harm should occur.

You could find some silicate salt bags to install temporarly in the bottom of your piano if it is used to a low humidity level (30% is a little low however, I would install an humidifier (cold humidity with air flow) it is not so expensive and very efficient, it even does not need regulation)


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If you can carefully lift the key out of the piano, flip it over and look inside the front mortise and see where the wear marks are on the cloth. If they are not decently centered front to back, the front pin might be binding on the end of the mortise. The key actually travels in a wide arc, not straight up and down. Also, check the key dip. If the front felt punching has compressed too much and the key goes too low, the bushing cloth might be binding on the pins in an unworn spot. There are other things that might be cause here to and I'm sure some fellow techs will chime in eventually.

As a mere pianist, could someone explain to me how a C# could be rubbing on a keyslip? Could the problem also occur with a Cbb?

Well, first off, keys do not get tighter with dryness. They become looser. They swell up with humidity.

C# can't be hitting the key slip but it can be catching the fronts of the C or D keys if the keys are not trimmed properly or have swollen up or have warped.

The first thing I would have tried was placing a butter knife between the offending keys to see if something had slid between them. That, is always possible.

Glad you're feeling well enough to post again, <smooch>

Thanks Jerry - Emmery's diagnosis had me very confused.

LOL you got me there Jerry. I missed the C# part in the OP. Keyslip would not apply there. As Jerry mentioned, something may have fallen in there and lodged in way that causes this. Sometimes the plastic laminate cap on sharps can come loose and bow out enough to rub or get caught up on the keys beside them too like the picture below. Some smaller drop action and direct blow pianos might not have sufficient weight to bring the key back up every time also and need some jiffy lead for help.

verified lately at 70% and 30%, the cloth swell, not the wood.

No problem Emmery, We ALL get caught from time to time!

Issac,

You sure do like to find room for a disagreement don't you? Give it up will ya?

P.S. Thanks Rag-doll!!

Certainly some PTG memeber have made experiments with the way aperture works in a key under diffenet moisture levels.

WHat I noticed is how the balance pin is tighter in winter.
For the mortise it may vary depending of the wood and the cloth but, as the hole is less large than the key, even if it enlarge by wood retractation on the externalm layers, in the end the key is thinner and the hole more tight. (that is the story of the hole in wood, I have seen an article on that subject in the journal, me think)

The cloth loose its moisture and get thinner, that may cause more side play in winter eventually. but friction on the pin at the balance is higher, enough to make avertical note fail repettion.

In winter, it is also better to take the action out and install the treble on the bass side, for that reason.

Please notice that pianos make also a neat place for birds when the weather is cold.

There could have been something stuck between the keys that dropped when the key moved.

Humidity changes cause wood to both swell/shrink and twist with the grain. The key is, (we hope), originally fitted to work at normal humidity ranges. So both increases and decreases can cause the key to twist and develop sluggish bushings.

Thank you for all the responses! I've been ripping out carpet and cleaning for the last 48 hours. Humidity is down to 60% and C# is still working fine. The piano is away from the wettest area and I have a small fan circulating air around it.

I'm going to try the butter knife approach tonight. The key is not visibly in contact with C or D; there's a nice uniform gap all the way around the key.

The insurance man was out today. I think I'll have enough left after repairs that I should be able to get a technician out to look at it.

Thanks again!

OK; passed the butter knife test. But, I was able to replicate the problem by pressing the key down very slowly. There is a moment at the bottom of the key's travel that I definitely feel a shift in the balance of something. Maybe the resistance suddenly disappears?

Is that possible, or am I just nuts?

As I said, I can't see any physical difference in the key or the mechanism from any other key or mechanism when I open the top door.

Thanks again; I appreciate your help.

that doesn't totally eliminate the fact that the key could still be the cause. Like I said, it could be the front edge of the sharp catching on the back edge of one of the two white keys or, maybe it might be the bridal wire is catching on the neighboring wire. Could be lots of things.

This point of increased, then decreased, resistance is in itself normal behavior. It has to do with a process called let-off (or in the UK, I've been told, set-off). It's the point where the jack is disengaged from the hammer butt, which (on a normal blow) sends the hammer assembly into free flight towards the strings. You should find much the same behavior on neighboring notes.