I no longer pay any attention to these prescriptive parameters, as they are all based on assumptions of geometry, which may or may not...usually not...be present in the actual as-built action. When I tried to apply these prescriptions, without understanding the full system geometry, for several years, I left a trail of lousy checking actions; an MO if you will..."lousy checking, Ialeggio must of been here". The geomtery's were simply not described by these parameters with any regularity, either between pianos or within a particular piano.
They assume, or have to assume, a certain check distance, 5/8, 7/16, 3/8. They have to assume a certain key dip, .390, .40, .410, or more. They assume bore is correctly matched to string height across the compass ( an entirely fictitious assumption, unless custom bored well...and even then still fictitious). They assume the out-of-cavity position of the action/keyframe is actually producing the targeted dip per each key, when tested. They assume check height is correct for the check height chosen (another usually incorrectly targeted dimension, relative to the as-built conditions of a particular action). They assume string height is within certain parameters, usually pretty close to 7-3/4" or so.
Once I started ignoring these instructions, my check installations, instead of being my achilles heal, improved significantly.
Check happens, geometrically, at one point in the intersection of the involved arcs...that's one point in the universe. Thankfully, give in the system widens the range of effective check, a little, but not much. Where that point will occur, in a particular action or manufacturer's action will vary as per the geometry of that installation. All geometry's vary, even model to model for a particular manufacturer. That geometry also changes across the keyboard of an individual piano.
This whole thing is quite present to me, as I work on a lot of Chickerings, and redesigns of Chickerings. What does that, or any prescription, do when faced with a 7" string height action, when the prescription is based on a 7-3/4" string height, or when dips are shy by modern standards.
Instead, I take each and every action as a unique geometry or collection of geometries, and empirically ask the geometry where those arcs will intersect in that particular action. Its rot gut simple to lay out, and leaves all the prescriptions to confuse somebody else.
Not sure Eric wanted to take this to layout procedures. I can post if there is interest. But I did want to convey how, to me, these prescriptions are wildly confusing to counter productive, and do not confer understanding of the system's geometrical requirements. By the way, even though I love what WNG is doing with their parts, their installation protocols are prescriptive as well. They make all the disembodied assumptions outlined above, and preclude an understanding of the geometry involved in the use of their particular design of the check and tailing tools. And they also change prescriptions from time to time, leaving one scratching one's one's head trying to reconcile previous prescriptions with the new improved prescriptions.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 08-30-2020 02:10
From: Joe Wiencek
Subject: backcheck regulation
Eric,
What I have read is the 2 mm gap is before bending (after installation.) Richard Davenport mentions a 1 mm gap, and I think this after bending (which may be equivalent.) An interesting question about what may be sacrificed by a longer tail, and though I don't have an answer, I will ponder it. Thank you for the question.
Joe Wiencek
Original Message:
Sent: 8/29/2020 9:12:00 PM
From: Eric Johnson
Subject: backcheck regulation
What is the reason for the backcheck to hammer tail distance spec of a 2mm gap (when not in check)? I'm assuming it affects repetition but it also seems (to me) like careful bending of the backcheck wire would/could make up for it as well as the fact that the shape of the tail can mean the difference between success and failure.
What is sacrificed if the hammer tail rests 2mm below the top of the backcheck?
Thanks for considering
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Eric Johnson [RPT]
[Eric Johnson Pianos]
[Westport] [CT]
www.ericjohnsonpianos.com
One year older and dumber.
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