TROPICS IV: Tropical keyboardsEntire Contents Copyright © 2010 CBH
|Keys requiring alignment
A general slowing down of the action is often the first evidence of high humidity. The keys can become sluggish, and eventually stick down. Once the keys are eased and the instrument is played regularly, they rarely give more trouble.
Some diagnosis is required first of all to make sure that the true problem is corrected. Most usually, the balance mortise around which the key pivots like a see-saw, has expanded with humidity to grasp the top of the balance pin too tightly. This mortise in the top of the key must have parallel sides, a fraction wider than the balance pin to avoid friction, and sometimes must be repunched. The hole in the bottom of the key must always remain circular where it surrounds the pin, otherwise the key can slide from front to back and will never be reliable.
The rear end of the key can be guided in different ways depending on the instrument type and make. Perhaps the soft iron guidepin which works in the rack has rusted a little and requires the corrosion to be polished off, or maybe the guidepin needs filing a tad narrower because the slot has shrunk with humidity.
On upper keyboards, the guide pin mortise could be grabbing the key too tightly—this system works the same way as the top of the balance mortise, but the key bottom at that point is normally cut in a large circle to clear the pin entirely.
Some makers use plastic inserts at the balance or guide points. These enable a keyboard to be made faster, but are not to be found on high quality instruments. They can squeak, or become ragged or even dislodged.
In a misguided effort to reduce or avoid keyboard problems, some makers have resorted to using MDF for the keys. This reconstituted wood product is heavy and in practice not as quietly climatically stable as the makers would have liked to believe.
Only the cheapest and nastiest keyboards are made by individually cutting a number of C keys, D keys, etc. Such keyboards are disasters waiting to happen, and instruments with them are probably best avoided. A good keyboard is made from a several flitches glued into a single plank. The keys are sawn apart only after the keycovers are attached and rails have been drilled through the plank.
Keys can also warp or twist, particularly those which have a join between flitches. You would expect your keyboard to require some simple leveling and spacing after a year or two of playing, no matter what environment your instrument is housed in.
Sometimes an odd key can just have simply expanded in width enough to rub on its neighbor, especially if the sides of the keys were left rough from the saw by the maker. Here it may be necessary to plane a small amount off the side of the offender. The keyend cloth could be interfering with the adjoining key, so it is worth checking if that requires trimming first.
To bring a keyboard back into good regulation, the first adjustment to make is the tilt. This ensures that the playing surface of all the keys runs flat. If you see a key has one of its front corners lower than the other, the tilt must be adjusted by knocking the top of the balance pin slightly sideways. The keys are then leveled using paper punchings under the cloth balance punching on the balance rail. Then the heads of the naturals are spaced laterally, the sharps dividing the space evenly, and any adjustments made at the tail end of the keylevers to allow adequate clearance there.
Any keys which are radically out of alignment may require a wedge inserted to bring them true.
|A keyboard frozen with lead expansion
Key lead expansion
Lead used to balance keys will also corrode, with its tell-tale white lead salt—reported to be lead acetate, Pb(CH3COOH)2—expanding from the sides of keys. This usually happens in instruments after some decades, but again the corrosion is accelerated in areas of high humidity. The problem is first noticed by a few keys being sluggish or sticking down entirely.
Soon an entire keyboard is frozen, obviously rendering the instrument completely unplayable. The repair is much more drastic when the keys are radically deformed and split.
|LEAD IS TOXIC:
AVOID IT IF YOU CAN.
Some individuals are sensitive to lead, and care must be taken in any case because lead is an accumulative poison. Many countries have removed lead from petrol—don’t get your dose from working on your harpsichord. If you must do this task, often the best method is to use a sharp chisel to shave the offending corrosion off level with the key. Be careful to dispose of the waste without unnecessarily breathing in any dust.
The shaved leads will in all likelihood continue to corrode, and the job may require repeating in the future. A longer-lasting but more involved repair would be to remove the corroded leads entirely, repairing any split keys, and rebalancing with a non-corroding lead alloy like that used for stained glass windows.
|Antique piano keylevers splitting with lead expansion
Timothy Murray demonstrating how to balance a French Double Harpsichord lower manual key.
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