Steinway M Backcheck Problem

[David Skolnik]

Al -
You have gotten a good deal of useful information in response to your 
question.  The problem is a lot like pizza.  How can something which 
seems to have so few ingredients come out so different? Well, without 
actually knowing the answer, I'll tell you what I think.
Pinning - It's true that excessively tight pinning in the repetition 
lever, hammerflange, and even the jack*, could have a negative impact 
on the checking, but you seem to have eliminated that factor.  Of 
course, the assumption with regard to the pinning is that the 
elevated friction prevents the hammertail from addressing the 
backcheck with enough velocity to both a) sufficiently compress the 
rep spring, and b) adequately engage the frictive (not a real word) 
forces that will counter the restorative impulse of the compressed 
rep spring. Of course, depending upon factors mentioned in previous 
responses, such as the effective tail to backcheck distance at 
let-off, the distance the hammer has to travel (downward) before it 
even makes initial contact with the backcheck will affect how much 
spring compression has to be overcome (to maintain checking).  Once 
checking has been accomplished, that pinning friction would seem to 
add some resistance to the un-checking impulse of the rep spring.  If 
the pinning is not the real problem, reducing  the friction will 
undermine other aspects of the action's response.

Roughing tails / backchecks - As you pointed out, you've been able to 
accomplish checking without such measures when you do your own 
shaping, so, as with easing the pinning friction, this is more likely 
a compensation for some other failing in the process.  We could get 
microscopic, and examine what such roughing is actually doing (or not 
doing), but, when treating the tail thus, you would likely be 
accelerating the wear on the buckskin, and roughing the leather would 
seem likely to, at best, create an uncontrolled nap (remember nap?) 
which could work equally against the initial 'grab' function.

Shape - Obviously, there are MANY different concepts of both tail and 
backcheck profile which seem to work.  The point is how the two work 
together, and in conjunction with the other factors that create 
checking.  One thing that I did not see mentioned, with regard to 
shape, is the congruence of the faces of the tail and backcheck, 
specifically at the contact surfaces.  I have corrected many such 
misalignments, on both new and rebuilt actions.

How backcheck functions - In the context of the current technology 
(thus excluding velcro, magnatism, etc.), there is a friction 
component,  a spring component, and a mechanical interface component.
- Ideally, friction should be the least active, since it is hard to 
limit the action of the friction to one direction.

- The mechanical interface should achieve adequate surface to surface 
contact and engage with the least amount of shock, but sufficiently 
defined so that it functions consistently, thus the importance of 
complementary profiles.  Related to the profiles, the reference above 
to "effective tail to backcheck distance" refers to the actual point 
at which the two would engage, depending upon their profiles, rather 
than the simple measured distances of each extremety (tip of tail and 
top of backcheck) from a defined base.

- That leaves the spring function, which is achieved by the combined 
deflective behavior of the backcheck wire, the backcheck felt, and 
buckskin (or synthetic) covering.   All other things equal, that 
combined spring function controls the checking.  For example, you 
could, in theory, have a totally rigid 'wire' if the correct quality 
felt and skin were employed. The resilient qualities of the 'skin' 
material has as much of an effect as the surface 'nap'.  That said, 
the newer type backcheck wires, considerably more rigid, have to have 
a profound difference on backcheck behavior.  With regard to Bill 
Monroe's statement:
>I wouldn't concern myself where the bend is to establish the angle 
>as long as the angle is correct.
the effect might be subtle, but I can see where the location of that 
bend would, in fact, have an impact.  For example, a wire emerging 
from the key stick at the correct angle uses its entire length as a 
spring.  A vertically installed-then bent wire creates two shorter, 
stiffer 'arms' which may not function in the same way.

Last, but probably most to the point, you said:
>The tails are quit rounded now. Do you think they should be a little flatter?

For sure.  With excessive rounding you have two problems. First, you 
reduce the effective contact surface. Second, you lower (increase) 
the effective point at which tail and check first contact, since the 
check must still be set back enough to clear the 'bump' in the tail, 
but now contacts a point further up on the tail than it would were 
the tail flatter.

That's my brief response, I guess.

*Theoretically, if jack is pinned too tight, tension of butterfly 
spring would have have to be increased, which would have an impact 
upon hammer rise, etc.  It's a stretch, perhaps

David Skolnik RPT
Hastings on Hudson, NY
I could be wrong









At 11:47 AM 3/13/2008, you wrote:
>I am regulating a 10 year old Steinway M with all original action 
>parts. I am having a problem with checking. The piano checks 100% on 
>the bench, but no checking at all in the bass section and 85% OK in 
>all other sections.  I have adjusted the angle on the backchecks 
>with no success. Does anyone have any thoughts on what the problem 
>my be and a possible fix?
>
>Al Guecia
>No virus found in this incoming message.
>Checked by AVG.
>Version: 7.5.519 / Virus Database: 269.21.7/1327 - Release Date: 
>3/12/2008 1:27 PM

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