Good at Machining WAS: Reading a Board geometry

[Farrell]

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You want to measure the angular relationship of the string in three =
areas: along the speaking length; along the bridge top; and along the =
backscale just aft of the rear bridge pin. Those measurements will give =
you all the data you need to characterize downbearing.

Be aware that all these references to setting bearing to "the thickness =
of a nickel" or whatever level above some reference point may be fine =
and dandy, but are completely dependent on the length of the backscale. =
As the backscale length between two systems where this type of =
measurement is being used varies, inaccuracies in the reference =
thickness will be introduced.

How much downbearing is desirable will depend on the soundboard assembly =
design, where you are in the scale, and a host of other factors I know =
very little about!

Terry Farrell
  ----- Original Message -----=20
  From: Crashvalve@aol.com=20
  To: pianotech@ptg.org=20
  Sent: Monday, October 06, 2003 7:38 AM
  Subject: Re: Good at Machining WAS: Reading a Board geometry



  In a message dated 10/6/03 12:54:05 AM, yardbird@vermontel.net writes:



    I'm assuming you've got some sort of milling machine, not =
necessarily
    a Bridgeport. I bet you could do a good job of making a component
    downbearing gauge, the one with the adjustable inclination bubble
    mount. Someone send this guy a .jpg of one (not necessarily
    identifying its maker).

    Bill Ballard RPT
    NH Chapter, P.T.G.




  Living near Detroit I have acquired lots of machinery from old tool =
and die shops. To do credible work you need both a mill and a lathe and =
a lot of support tooling. Can be a time waster in that one of three =
experiments is good to go. Re the downbearing gauge I bought one from =
one of the suppliers years ago and returned it because of the low =
precision bubble vial. Your best bet would be a simple jig with a place =
to temp. mount a machinist's level. A good one is accurate to .005 per =
foot and a REALLY good one goes .0005 per foot. Question is (and this =
goes back to the vector discussion in recent threads) what do you want =
to measure, which two surfaces to you want to relate to each other ? =
Even S&S once specified thickness of a NEW coin for down bearing =
gauging, or was that just romantical hype ? 
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