Steinway M Backcheck Problem

[Mike Spalding]

David,

Good comprehensive summary of the issues, and I agree with you on all 
points, particularly the folly of roughing the tails or check leather.  
If roughing improves checking, there is an unresolved problem somewhere.

I like to think of the backchecks and tails as a self-locking taper.  
This is the same mechanism that keeps the chuck in your drill press.  As 
long as there is some amount of friction, no matter how small, there is 
a taper angle below which the taper will lock, and above which it will 
fall apart.  In the context of backchecks, if the check is laid way back 
then adjusted to contact near the tip of the tail, the hammer will 
bounce off the check.  Go to the other extreme, with the check near 
vertical and contacting up near the shank, and the hammer will check, 
but not at a consistent height: the harder you play, the lower it will 
check.  Somewhere in between is the optimum, where the hammer will 
reliably check,  and will be difficult to push further down.  
Admittedly, there are pianos where this sweet spot is not easy to find, 
especially in the low bass.

Mike

David Skolnik wrote:
> 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
>