Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum How much side to side play should keys have?

And what is the purpose of having any at all(or is it unavoidable because of other constraints in construction)?

None, or as close to none as is practical.

As little as possible so as to not impede the movement of the key.

If the side play is ideal, the side play is actually you compressing the bushing felt. Less than half a mm overall, including compression.

Friction resistance becomes a problem if they are too tight.

My rule: enough to feel but not hear. I.e. When the key is moved side to side firmly and quickly, you can feel the key moving but not hear it. You need a little movement so that in humid situations the keys don't get slugglish. (So, leave a bit more looseness in winter if yours are dry.)

I do not know if this is the correct way to think about or define it, but when I said "side to side play" I meant how far one could move a key if one actually grabs the front of the key and tries to move it. I found on my 6 year old Mason BB I could move the key around one third or half of the distance between the sides of the keys(the empty space between the sides of the white keys).

As little as possible without introducing unnecessary friction. Sizing the bushings with special heating broaches irons down the fibers for reduced friction (and it sizes them accurately), key pins should be polished with Flitz and lubricated with a dry film lube such as Protek or McLube.

If you can move the keys half the distance of the space between them, then they could begin to knock against their neighbors. That would definitely be way too much key travel.

Key bushings need replacing after some time/amount of wear. Factors contributing to key bushing wear are numerous and include keyboard design, materials used, piano servicing, amount of playing, playing technique etc.

That is definitely too much side travel, Pianoloverus, but ideal travel always has to be slightly greater than zero. When you move a key side to side it should have the slightest visible movement with moderate pressure, before the bushing is compressed.

The point of slight side to side tolerance in my mind is really to calibrate key friction. This has to be done looking at the inertial characteristic of the key after bushing work is done. There will be variation in the bushings, so side tolerance will have to vary key to key.

The end goal is to have a slightly dampened movement over the front pin as part of the action's energy dampening system. The key should settle with a slight 'fluff' over the pin.

often 0.4mm given as a rule, for cloth, a little more with leather, while I dont get the reason for that.

keys get tight in winter and more loose in summer

Maybe the other way around you mean Isaac? The cold here in the winter makes the heat dry all the woodwork...

Hi Dan, because it dries the wood is closer/tighter, but the cloth is thinner , under dry conditions.

if you notice more play in winter it is due to the cloth, not the wood

The balance hole is more tight in winter, because the hole is a small dimension in regard of the size of the key.

The dimensional change of cloth is huge, I just noticed on a vertical piano where I regulated the play of the top of the jack a hair tight, in a dry room, then the window was left a little open for half a day, and it rained.

All the hammers where moving 1/32' when pressing on the key near the capstan.
Just the moisture that thickened the cloth.

for the balance mortise 0.2 mm. can be tested with a thin blade of the good thickness, it help to get an even play

Perhaps things are a bit different across the big salty pond in Kamin country. They loosen up here in the Frozen North ... and how!

Check the balance pin, David, not the mortise, the mortises can be tighter or larger depending of the wood and the cloth.
I dont have a survey and I also have believed for long that the apertures in the keys enlarge with winter dryness, while the wood retract, once I understood that I checked the balance fit and it is tighter in winter.