Bass hammer checking

[Phillip L Ford]

On Thu, 14 Mar 2002 20:44:57  
 jolly roger wrote:
>
>Hi Phil,
>             Your problem is probably poor tail arc, and or check Rake,
>(angle)   The radius of the tail needs to be 2 1/2" radius, and square with
>the
>hammer rail. Back check angle about 22 degrees back from vertical. And the
>check height needs to have the centre line of the shank, at the top one third
>line of the check at rest with the correct blow distance set.  1 7/8" approx.
>Hope this helps.
>Roger
>
Roger,
Thanks for the specifics.  I'll check these things.

To all others who replied (sorry not to mention you all by name) thanks for the
input.  For the record, since it was unclear from the post, I also am not a fan
of checkering tails or roughing backcheck leather.  But in some cases these
things do improve checking, at least in the short term.  My point was to show
that in certain pianos it seems that no matter what you do to the existing parts
(without changing length or shape of tail) you can't get proper checking. On this
particular piano I took off the glaze on the tail with sandpaper.  This piano has
new backchecks, so I didn't do anything to the surface of them.  Also,
I'm aware of changes in geometry as a result of keyframe flexing, but thanks
for mentioning it.  But, I think that this would account for a change in where
the hammer checks, not for it not checking at all, unless there were insufficient
keydip once the action was back in the piano.  By making the checking deeper
or shallower with the action in your lap you should be able to get the thing to
check eventually, even if it is checking at a different spot than it was when the
action was in your lap.  However, this was not the case on this piano.
One thing I forgot to mention was the rep lever pinning.  I had checked that and
it seemed correct to me.  I didn't think about the rep lever dragging on the jack
(thanks to whoever mentioned that).  I wouldn't have thought that keyframe
hold down bolts or dags would make a difference since the back of the key is
not on the keyframe when the hammers are in check.  However, since Joe said
that this corrected a similar problem that he had had I'll check it out.  Thanks,
Joe.

Phil F

>
>At 06:45 PM 3/14/02 +0000, you wrote:
>>Yesterday I worked on an older Baldwin with a Schwander action that
>>had a characteristic that I've encountered on other grand pianos,
>>some having it more than others.  The hammers check perfectly on the
>>bench or when the action is pulled out in your lap, but won't check when
>>the action is in the piano.  This behavior is usually only noticeable in the
>>low end of the scale and becomes most pronounced at the bottom.  On some
>>pianos it seems that you can't get the hammers at the bottom end to truly
>>check no matter what you do; make the checking shallower, make it deeper,
>>groove the tail, rough up the check leather, change the back check angle,
>>reduce rep spring strength to almost nothing, etc.  When I say 'truly check'
>>I mean behave as in the rest of the piano.  The hammer is held
>>some distance below the string when the key is down and rises
>>when the key is released.  Apparently some sort of 'checking'
>>is going on because even on a hard blow the hammers don't bounce back to
>>the strings.  But the tail isn't really being held by the backcheck when the
>>key is down.  What's the reason for this?
>>
>>Phil F
>>---
>>Phillip Ford
>>Piano Service & Restoration
>>1777 Yosemite Ave - 215
>>San Francisco, CA  94124
>>
>>
>>
>>2,000,000,000 Web Pages--you only need 1. Save time with My Lycos.
>>http://my.lycos.com
>> 
>


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