At 05:24 PM 2/20/98 -0600, you wrote:
>Hi David,
>
>First of all, how did you get bearing measured in thousandths of an inch
>from a gauge calibrated in 3/16 degree increments? Without knowing how the
>numbers were arrived at, it's hard to know what they mean.
Ummmmmmm...... Well, I will be the first to admit that I am not sure what I
am doing here! I have never used this tool before. But, the Lowell
Component Downbearing Gauge comes with a handy-dandy set of instructions.
Just to make sure we are both talking about the same tool, it is listed as
item CDB-2 on page B-7 of the Pianotek Supply Co. catalog.
The component downbearing gauge has a bubble level on the top, with an
adjusting screw to raise or lower the bubble level to calibrate it. The
tool has two little "feet" that sit on the wire being measured. The tool
is placed on a string in between the two bridge pins, and calibrated to one
of the lines as a reference mark. The tool is then moved to the rear
segment of wire between the bridge pin and hitch pin, and as the bubble
moves in the level, it will indicate the downbearing of that rear segment
of the wire. The tool is then moved to the front ("speaking") length of
the wire, and again the bubble will move to indicate how much downbearing
exists in the front string length.
The instructions state " Multiply the number of divisions the bubble
crossed by three, and one has the net bearing, in thousandths." For
example, I took this to mean that if the bubble moved 3 division marks from
the point where it was calibrated, that would mean .009" of downbearing (3
division marks, x .003" each = .009").
The instructions don't say that the tool is calibrated in 3/16 degree
increments.
>Second, did you check the crown of the board? Crawl underneath with your
flashlight and state-of-the-art black thread for use as a straightedge and
make sure there is crown.
Oops, didn't do that.
>Check at more than one spot, especially under that D4. These
>numbers are too weird, maybe you can clarify a bit?
>Ron
I was hoping that you could clarify! The numbers seem weird to me too, but
I don't know what reasonable downbearing would be for a piano. The reason
that
there is a large gap between measurements between A2 and D4 is that I
didn't measure the tenor strings where they cross under the bass strings.
>At 03:24 PM 2/20/98 -0600, you wrote:
>>Note Rear downbearing Front downbearing Tail length
>>B0 -.027" +.021" 3"
>>B1 +.003" +.021" 3 3/4"
>>E2 +.024" +.030" 4"
>>A2 +.036 +.033" 4 1/2"
>>D4 0.0 +.006" 4"
>>C#5 +.010" +.015" 3 3/4"
>>E5 +.012" +.009" 3 1/2"
>>F#6 +.015" +.006" 2"
>>A6 +.015" +.015" 2"
>>F7 +.003" +.003" 2"
>>C8 +.005" Couldn't measure 1"
This piano had a new bass bridge made that looks great to me. But these
downbearing readings seem to indicate that there could be way too much
downbearing in the bass, if I interpret this correctly.
One last question... I know that downbearing measurements can be calculated
to indicate how many pounds of downbearing exist in a certain string.
Downbearing can be expressed as the amount of force that the string is
pushing down on the bridge (for example - 1.9 lbs).
But is it possible to express downbearing in thousandths of an inch like I
did?
I just got this tool last night, and I stayed up late reading Nick
Gravagne's articles in the JOURNAL from 1989 and 1992. I guess I just got
carried away! The April 1989 JOURNAL has Nick Gravagne's article on
Lowering the Plate: Part 1. It had some calculations on Page 31 about how
to figure the bearing angle using trigonometry [which my wife explained to
me :-) ] and I was hoping to figure out how to change the readings in
thousandths of an inch to readings showing degrees of Bearing Angle.
Thanks,
David
David A. Vanderhoofven, RPT
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