• 1.  action spread

    Registered Piano Technician
    Posted 07-15-2022 22:25

    When I was new to this business I bought what was called the Piano Action Handbook, put out by the PTG, 2nd edition 1971.   It had all the figures for key height, dip, checking, etc. of a wide variety of models and brands.  I've since realized that most of these figures resolve themselves when you start to regulate the piano and I've not used that little booklet for years.  I keep it solely because every once in a while I'll want to remind myself of the recommended spread for an action and I decided that would be a good place to keep that miscellaneous nugget of information.  So inside the front cover I've written:  "Yam  112.5 mm;  All Bald  4 27/64".  I forgot where I got this figure in the first place, but it wasn't printed in the booklet. (This is the best argument for converting to metric that I know.  Most of these measurements have some latitude, but not the spread.   But 4 and  27/64"--who can be expected to remember that?)

    I recently brought a Baldwin M into the shop.  It had issues that were mostly related to wear and tear: There were two indications that the spread had been altered:  #1 there is gap between the whippen rail and the stop on the action bracket and #2 there is a line drawn in pencil, rather faint now, down the backside of the knuckle core and another scribed on the side of the whippen that are apparently supposed to match up.   You'll notice that the jack currently lines up incorrectly with the front of the knuckle core.

    The current action spread is 111 mm.  But if you move the whippen rail forward against the stop cast into the action bracket, presto you now have the correct spread of 4 27/64" and the jack now lines up with the back of the knuckle core as it should, not the front. Problem solved?

    No.   Actually, now, with that little shift of less than 2 mm, the action won't regulate.  Level, dip, key height are all unaltered but nothing else now works.  You can't get escapement for love or money.  With the "correct" spread it is quite literally impossible to regulate this action properly.  

    Now it was apparent that I was on a path that the previous technician had trod before me.  When I put it back to where I found it, suddenly everything regulated just fine, though the jacks needed to be brought back under the knuckles.

    Now my Action Handbook reads: " All Bald  4  27/64", except M  111mm."

  • 2.  RE: action spread

    Posted 07-16-2022 00:25
    Baldwins had various action spreads. I would align the notch on the rep lever (pencil mark) with the back of the knuckle core.
    Another guide is for the knuckle core to point at or align with the jack center at rest. Another aspect which is overlooked is action elevations, the Wippen Flange Center Height should be 64 mm below the Hammer Flange Center Height. Put another way: HCH - 64mm = WCH.   Things may not align well if the hammers are worn and are shorter than spec.

    Notations I have in my book under Baldwin:
    4 27/64" = 4.42" = 112.3 mm (L, R, M, B) (Chickering 410507 <?>)
    4 7/16"   = 4.44" = 112.7 mm (MP)
    4 31/64" = 4.48" = 113.9 mm (SD10, SF12)

    Pick one that works.


    Jon Page