Action flange crushing

[Dave Nereson]

----- Original Message ----- 
From: "Phillip Ford" <fordpiano@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, November 20, 2004 9:29 AM
Subject: Re: Action flange crushing


 >(just make the screws tight enough
> and shut up), but it amazes me that on something this basic there seems to 
> be no industry specs or data.

    Oh, there probably are, but they may use them only in the factory or 
when designing a new action.
    In repair manuals for cars, they give the torque specs for the engine 
bolts.  Well, with the head bolts, you may have future problems, like a 
leaking head gasket, if they're not all at the correct torque.  But with an 
oil pan bolt, it's not as critical.  Only the most persnickety mechanic 
would actually measure the torque of the oil pan bolts.  You just tighten 
'em 'til they're "snug plus another half a turn" or so, but before you're 
distorting the pan.  And it turns out that this will be very close to the 
specification (10 - 15 ft-lbs).
    The analogy to pianos is that the plate or pinblock screws might be more 
critical, but the flange screws just have to be tight enough to keep the 
flange from creeping, but not so tight that they distort the wood, causing 
misalignment or even binding of the center pin.  I'll bet what most would 
consider "snug plus another quarter turn" is very close to any factory spec 
for flange screws.

 > I think much investigation into this topic would quickly show that
> wooden flanges and wooden rails (or at least wood screws into wooden 
> rails) are a bad idea with regard to consistent action screw torque, 
> assurance of no flange damage in the short or long term, and long term 
> flange tightness.

    Probably so, but I've yet to see a split or warped main action rail in 
either a grand or an upright, and I've run into many many pianos where the 
action screws have been tightened only once or twice in 100 years, and yet 
the parts are still in good shape, reasonably aligned to the strings, evenly 
spaced, and sometimes, still tight, if the piano hasn't changed climates 
much.
    --David Nereson, RPT