[pianotech] How to work out distance of action from the plate?

[Mike Spalding]

Mark,

I don't see any other responses, so I'll jump in.

It sounds like you're talking about a vertical piano, not a grand, yes?  
And are you using "Height" to refer to the horizontal distance of the 
action from the plate?

I've never been in the situation you describe, being somewhat obsessive 
about marking and measuring during disassembly.  But I have put some 
thought into whether the original relationships could be improved upon 
during reassembly, so here's my thoughts, and I hope the list will join 
in and improve upon them.

Height.  For me, height refers to the vertical positioning of the action 
above the keybed.  Height will affect the strike point, which has the 
greatest affect on tone in the high treble, so set this end first, based 
on what you hear at note 88.  At the tenor and bass, raising or lowering 
the action will misalign the hammers with the strings.  If tenor hammers 
are too far to the left, and bass hammers are too far to the right, then 
the action is too high at that end.  So set the height at the bass end 
to minimize the amount of hammer traveling/shank burning you'll have to 
do.  If a good hammer/string alignment can't be achieved, review shank 
length and hammer rake.

Distance from plate.  Here you're looking for a good relationship 
(angular) between the jack and butt both at the beginning of the 
keystroke and letoff, and a blow distance that's appropriate for the 
action.  I would start with jack-to-butt at rest.  watch the tip of the 
jack returning under the butt, with the capstain adjusted for minimum 
lost motion.  If the jack seems to squeeze through a tight spot as it 
first gets under the butt, then emerge into a loose spot when it's fully 
under the butt, then the hammers are too far back at rest.  Shim the 
rest rail up with some felt and try again, until the jack-butt friction 
is uniform through the stroke, or maybe gets a little tighter as it goes 
in.  (If the butt leather is old/compressed/worn, this test won't tell 
you  what you need to know).  When you're happy with the jack/butt 
relationship, set the action-to-plate distance to achieve the desired 
blow distance.  Now set the let-off, and make sure that nothing bad is 
happening at that end of the stroke.  Basically, if you've got full 
power up to let-off, and a smooth let-off, you're OK.

hope this helps, and hope I interpreted your question correctly.

Mike

Mark & Janine Davis wrote:
>
> List,
>
> I do not think my subject heading is well worded, so I will have to 
> explain myself.
>
> I have come across some pianos where a restorer has removed the plate 
> with all the bolts and screws including the action standard bolts and 
> then have put everything back together again.  However in the process 
> of removing and replacing the plate, it seems that the measurement for 
> the height of the action standard bolts has been mixed up or forgotten 
> and now the action is to one degree or another warped and also sits at 
> the incorrect distance than it should or was originally.
>
> I have thought about it but have not been able to work it out.  How 
> does one work out the correct distance of the action from the plate or 
> from wherever one measures it from?  I do not know where to measure it 
> from, I have thought maybe from the plate, maybe the soundboard, maybe 
> the strings but where is a point that is uniform or reliable that one 
> can measure from and how does one go about it?  Phew!!!  What a long 
> winded question?  Sorry?  I am not able to ask it simpler or in fewer 
> words.  I hope you understand and are able to help, your responses 
> would be appreciated. 
>
> Thank you,  
>
> Mark
>