Ancient Backchecks?

[David Ilvedson]

Make sure your hammer tails are the correct shape...circular curve with a 3 inch radius.   To understand that shape, use a compass with a 3 inch radius.    Clamp each section and use a drill with a sanding disk.   60 grit.   Look at the shape of the drawing and approximate the curve of the hammer tails.   The  friction in hammer checking is the wedging of the hammer/center pin circle and the balance pin/backcheck circle.   A roughed up backcheck is mostly unnecessary if all else is right.    Also the back check should be as high as the hammer shank at rest.   Lower than that will cause problems.

David I.

----- Original message ---------------------------------------->
From: Richard Cromwell <rcromwell1@msn.com>
To: 'Pianotech' <pianotech@ptg.org>
Received: Mon, 12 Jul 2004 23:10:20 -0400
Subject: Ancient Backchecks?


>Greetings List!

>I have a question regarding this absolute nightmare of a piano action (1927
>Chickering - 5'8") I've been fortunate enough to have on my bench for the
>past few weeks.  After countless repairs, I get it back together and while
>rough regulating it I find it impossible to get consistent backchecking.  

>When the action is on the bench, I can get he hammers to check, a bit low...
>but at this point I'll take what I can get.  When I duplicate the string
>height over the hammers with a jig and then play a mezzo forte/fortissimo
>blow - I get mostly no checking and a lot of double bouncing.  The jack is
>escaping... so I can only come up with a few reasons why this is
>happening...

>1. The rep spring is too strong... unfortunate because they are really
>difficult to get to on this beast. I don't think this is the culprit, or at
>least the only one.  My guess is... 

>2. The fact that the backcheck leather is 80 years old, misshapen and worn
>smooth as a baby's bottom where the hammers should be making contact.  It is
>almost to the point of being spongy in look and consistency.  Not leather
>like at all. This leads me to a few questions... is friction in regards to
>backchecking coming more from the wedge like positioning of the hammer and
>backcheck when they come into proper contact? Or, is it from the tail
>rubbing up against the rough surface of the leather? (I know the answer is
>probably a combination of both - but what I really want to know is how
>important is it to have good condition leather on the backchecks? - thus
>justifying their replacement.)

>3. Also, at some point in this piano's lifetime a well meaning fellow
>attacked it in an attempt to repair it.  I can go on and on about the old
>botched repairs I've fixed and crooked keytops etc... But I won't.    But
>one thing I will mention is whomever it was put new hammers on the old
>shanks, could it be possible that they were bored and/or had their tails
>shaped incorrectly (too short) - thus leading to the checking problems.

>Now if it is determined that the misshapen and ancient backchecks are indeed
>the guilty party and we ignore the misshapen hammer tail/improper boring
>hypothesis... I have never had the pleasure of replacing a set of
>backchecks, how difficult is it? I removed one as a test and it sure wasn't
>easy to get out, I can't imagine it being very easy to get the new ones back
>in.  There is little information out there on backcheck replacement... so I
>turn to you my esteemed colleagues! Please offer up any hints, experiences,
>help, aid, sources of information, etc. that you may have to offer.

>Thanks in advance.

>Richard Cromwell
>Cromwell's Piano Service
>Detroit-Windsor Chapter
>_______________________________________________
>pianotech list info: https://www.moypiano.com/resources/#archives