Square piano hammer alignment

Hello jackrail,

Last Summer, I did a bit of work on an early-19th-century square piano,
a 6-octave Clementi, with the through-the-soundboard extension for the
top notes. (very similar to this one:
Clementi pianos, though somewhat earlier)

For the most part, I was just tuning and adjusting dampers and
regulating the action, none of which was particularly difficult.

Unfortunately, for some of the notes in the extension at the top, the
hammers are misaligned, and strike the wrong strings. There’s very
little tolerance here, since the pairs of strings are just a few
millimetres apart! With the lower notes, it wouldn’t be hard to tweak
the hammer alignment, since there’s a pin holding the hammer in place,
but on the extension notes, there isn’t anything at all besides the
parchment hinge. I’m at a loss to think of a way to regulate these top
hammers! Of course, the hinges can be replaced, but how to get the
hammers aimed correctly in the first place? You can’t even see where
they’ll hit until the action is put back in the instrument, and there’s
absolutely no way to adjust anything while it’s inside.

I’ve been wondering ever since how one would adjust these hammers, and
my searches on relevant sites (https://www.squarepianotech.com
especially!) didn’t turn up anything about this little detail.

Surely someone here has some experience with these?

Dear Jon-o

A good number of those squares of that period with the “additional keys” have that part of the keyframe split at the rear, leaving the box of the hammers and under hammers of the additional keys separate from the balance rail and front rail controlling the keys.

This enables you to optimally position the box so the hammers align the oblique stringing, and you can confirm by flipping the under hammer to push the hammer against the applicable string pair.

Here is a pic of a 1799 Broadwood in my workshop at present:



I don’t think this one was separate like that, unfortunately… as well, the whole section of keyboard is screwed down, so it can’t really be moved around much at all. Also, some of the hammers seem to be well-positioned, but a few are striking the wrong strings, so it really seems to be the hammers themselves that need to be adjusted. Here’s a picture of the hammers. I should have taken more pictures of the rest of the keyframe, but this shows the back of it, in any case.

I notice your Broadwood doesn’t have any pins to align the hammers either. Is it possible that the parchment hinges aren’t glued in, but just pinched by the screwed in piece above? That would make them at least a little bit easier to adjust, though a lot of trial and error would still be necessary, I think. I didn’t try unscrewing that piece while I was there, but maybe on the next visit, I’ll have a look!

Dear Jon-o

From their alignment, it looks like several of the hammers on your additional keyframe have been rehinged or even replaced. The hinges are definitely glued: The screwed cover rail adds stability and prevents the hinges from distorting when the under hammer pounds against the hammer shank to propel it to the string.

Broadwood did away with the guide pins piercing the hammer shanks mid-1790s, which meant more reliance on the leather (not parchment) hinges themselves.

With case distortion over the years, it’s not unusual to have to juggle the keyframe positions slightly to bring the hammers into best alignment. Even though they are screwed down, there can be some latitude. Sometimes you must fill the screw holes in the bottom and reposition slightly.

But in your instance, those individual hammers are well out of whack.