[pianotech] Capstan Line

[David C. Stanwood]

Noah,

Do mockups with the capstan moved in towards the balance rail.  Try 
finding a position were the key dip is more normal like 10mm and the 
blow like 45mm.  This should lighten things up..... you might have to 
cut the heels off and use new ones that satisfy the magic line...

David Stanwood

>      First, forgive me if this query is too long and arduous. I 
>should perhaps just hire an experienced Tech for a couple hours to 
>come and help me with this, but I'm trying to wade through it alone:
>
>      In checking the Geometry of this 1906 Spector & Sons Baby 
>Grand, my "magic" line seems to be much "mundane." The line runs 
>maybe 1/8" above the center of the capstan, rather than through the 
>middle of it; it doesn't even run through the center of the capstan 
>top - but slightly above. It's a little hard taking this reading 
>however since there's a small wood stabilizing foot (also the square 
>wippen rail) that gets in the way of my string, so that I have to 
>hold the string about 7/8" away from the key and carefully follow 
>the line of the string with my whole head so as to not distort the 
>view. Does that make sense?
>
>      When I push the keys down 5 mm, the hammer rises average 35 mm. 
>This gives me an MAR (Mechanical Action Ratio) of 6.75. That is way 
>too high no? Is 5:1 ratio ideal? Perhaps this high MAR would explain 
>why this piano "plays like a truck." According to my calculations 
>using John Dorr's Article in the November 2008 Journal, I would need 
>a 48.4 mm Hammer Blow to make my 8 mm key dip work (I didn't even 
>know anyone made actions with such low keydips.) However, my hammer 
>blow if I remember is (was, before i messed around with the Wippen 
>Rail) only 47 mm - and that's with the hammers resting on the the 
>hammer rest rail flet. (There is room to lower that Hammer Rest Rail 
>however if I choose to later).
>
>     I have no idea when this was last regulated - maybe decades ago.
>     I moved the Wippen Rail forward about 3 mm. From looking at the 
>magic line again, it looks like if I moved the capstans forward the 
>same amount it would become less mundane and more magical.
>
>     Now for My Question: Should I unscrew all the Capstans, plug the 
>holes and move them forward?
>
>     Or, is there another way to change the magic line that significantly?
>
>     Also, I'd like to get more into the Stanwood Touchweight, and 
>was about to start taking measurements but saw that it was a waste 
>of time with the magic line so out. The only measurements I've taken 
>thus far then are Down and Up weight, which averaged 61 DW and 23 
>UP.  I mention this so as to give more information, but also I guess 
>I have one more question: I need new hammers. These shanks have the 
>sloping knuckle that's built into the shank. Does it matter much 
>which Centerpin-to-Knuckle Spread I get? In drawing a line up from 
>the back of the jack, i got an 18 mm and 19 mm spread on the two I 
>measured. But that's the back of the jack, so that's not the correct 
>measurement anyway I think. Plus of course that assumes that the 
>piano was regulated correctly, which it probably isn't. I was 
>thinking of ordering the 17 mm Spread.
>
>     Thanks to anyone willing to help!