[pianotech] Lock Rail Puzzle

[John Delacour]

At 21:26 -0400 24/04/2011, Philip Jamison wrote:

>Take a small "rare earth" magnet (the little, very powerful ones) 
>and run it across the top...

That was a very good tip.  I used a not very powerful 3/8" x 1/4" 
magnet today and it gave me the position pretty accurately of 8 
equally spaced ferrous things, central along the rail.  So far so 
good.

At 23:40 +0100 24/04/2011, John Delacour wrote:
>If you look at the bottom of the picture you will see there is a 
>thin strip between the lock rail and the moulding.  This is a 
>separate part from the lock rail proper and probably holds the 
>secret of how the rail is attached.

Following this line of enquiry, I knocked out this fillet using a 
mallet and first a 1/2" chisel and then a long strip of hardwood 1/2" 
x 1/4" with a chiselled end.  The fillet was glued in but the glue 
was sparse so the fillet came out with no trouble.

One thing is certain, I think, and that is that the screws, if that 
is what is there, have not been turned in and then veneered over from 
either one side or the other, because I know it is impossible to make 
such a job perfectly invisible over 140 years.  And besides, it's 
just bad workmanship and would never have been considered by 
Brinsmead.

Next thing I did was hammer the lock rail, at the points where I know 
there are ferrous things, towards the gap left by the fillet.  My 
original guess when I puzzled over the point of that fillet, was that 
there are short screws with countersink heads in the top front half 
that engage with keyhole plates in the hidden face of the lock rail, 
the same method used by other makers in the longitudinal arrangement 
whereby you need to hammer the *end* of the rail (after trying to 
remember which end!) to release the rail.

For a while I had no joy.  I then fed in a little spirit under the 
rail from the fillet side in case glue was involved.  In several 
places the spirit wicked wight through to the blind side of the rail 
and I had to keep a rag handy to wipe it off quickly and avoid 
burning the polish.

The stage I'm at now is that I've managed by hammering to move the 
rail in about 2 mm at one end, and I'm leaving it at that until I can 
be sure I'm not heading for disaster.

There is no polish between the rail and the top and none there the 
fillet was, but I think it more likely that this was masked while the 
top underside was being polished than that the thing was polished 
with the rail attached.  Any French polisher knows that you don't 
make things so that you need to polish into corners.

Finally I can see no other possible use of that fillet but to lock 
the rail in position.  It adds nothing visually -- in fact it looks 
strange -- to it must have a mechanical function.

If anyone has time to dream up or puzzle out the ultimate solution, 
I'd be mode grateful.  I should have though of the magnet trick 
myself, but I didn't, so that was a bit of progress already...

JD