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Key Frame Bedding - Yamaha

  • 1.  Key Frame Bedding - Yamaha

    Registered Piano Technician
    Posted 05-14-2021 12:07
    I'm starting a new thread, based on ideas put forth in a thread a couple of days ago, titled Yamaha regulation/voicing problems.

    In that thread, Geoff Sykes cites instructions from Yamaha to have, as a point of beginning, glide bolts extending beyond the bottom of the keyframe by about 2mm.

    I am rebuilding the action of a 1965 Yamaha G3.  If I lay the keyframe, without the action stack or keys, on the key bed, with the glide bolts fully raised, the outer ends of the front rail float slightly.   If a little pressure is applied by the key end blocks, it lays flat.

    There are four glide bolts on this action, and no glides that are accessible only from the bottom of the key frame, as I have seen on a newer G3 in our collection.

    The action, as I found it, had the two middle glides practically flush with  the bottom of the key frame, and the two outer glides extending beyond the key frame by maybe a millimeter.  The floating of the outer ends of the front rail had been addressed by installing a pair of thumbtacks as front rail glides, one at each end of the rail.  Interesting.  I have removed them.

    I removed the action and most of the keys from the frame, leaving in place all of the C's as well as A0.  I lowered the glides such that they extended past the key frame by 2mm, then proceeded to bed the key frame using the newsprint strip method.  When strips of newsprint between the glides and the keybed could be pulled with medium resistance, I remeasured the position of the glides.  They were awfully close to where I found them when I first pulled the action.

    I understand that the Yamaha protocol is intended to position the glides at something other than one of the outside limits of whatever acceptable range exists.  I like that idea.  If bedding the key frame by the above method puts the glides flush with the bottom of key frame, and a change of  seasonal humidity causes the system to change such that further raising of the glides would be the desired, the whole key set regulation needs to be taken back to the drawing board.  I get that.

    I reset the glides to the 2 mm extension, and examined the relationship of the front rail to the key bed.  If I raised the mid-treble glide slightly, and messed with the key end blocks to force the ends of the front rail down to the key bed (using a .033 shim above the end pins), I could get the front rail to mate nicely with the key key bed.  I felt pretty good about it until I tapped the back rail.  It was hovering well above the key bed.

    By that point, I had already exceeded my allotted time (about 2 hours per week)  on campus under the existing restrictions, so I walked away from it.  Fortunately, I just got a call informing me that as of now I can again be present on campus for up to 20 hours per week.

    I pondered whether some kind of shimming of the dags would be a step in the right direction, but I'm more inclined to think that for the this piano, the 2 mm spec is not even close to what is needed.  I do want further experiment to establish whether there is an acceptable range of adjustments for the glides, and find something close to a center point that I can use for my base regulation.  I suppose I may discover that I in fact do not have a range of options, and will just have to settle for the one place where everything works, and hope for the best when the weather changes.

    As for the key end blocks, the brass plates have no allowance for vertical adjustment.  I'm thinking of cutting appropriate shims from acetal copolymer, and gluing them with CA into the slot to bear down a little more on the keyframe end pins.  Am I overthinking this?

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 2.  RE: Key Frame Bedding - Yamaha

    Registered Piano Technician
    Posted 05-14-2021 13:41
    > "...will just have to settle for the one place where everything works..."

    I think this should be the goal no matter where the manufacturer starts, or what the manufacturer recommends. 


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    Geoff Sykes, RPT
    Los Angeles CA
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  • 3.  RE: Key Frame Bedding - Yamaha

    Registered Piano Technician
    Posted 05-14-2021 13:58
    I agree, Geoff, but it's always nice to have somewhere to go when a change in humidity subtly changes the dimensions of the key bed or the key frame.  If there is some wiggle room in the final placement of the glides, I would sooner choose a point from which I could have a choice of directions in which to adjust, should the need arise, rather than having to fuss again with punchings when the one available option turns out be the one I don't need.

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    Floyd Gadd
    Regina SK
    306-502-9103
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  • 4.  RE: Key Frame Bedding - Yamaha

    Registered Piano Technician
    Posted 05-15-2021 11:29
    Floyd,
    Regarding shimming the brass plates that hold down the keyframe end pins- I think your shim idea would work (I’ve done similarly with strips of business card to adjust seasonally.) i recently learned a tip from David Hughes. Remove the plates and peen the area above where pin slides with a punch or drift. Do this on both sides of the plate. Then you might be able to just slightly adjust the cheek block screw tension to adjust seasonal pressure on the end pins.

    Joe Wiencek
    NYC