TR: push/pull dynamometer/Calibrated beam keyweight measure

[Sarah Fox]

For those of you who prefer using weights, consider also using a chain for
ease of measurement.  (It's not my idea.  It is actually an idea modified
from the old "chain-o-matic" precision balances.)  You would place larger
weights on the key less than the DW.  Then place a small cup of known mass
(e.g. 10 g) on the key, still less than DW.  Then, holding the end of a
small chain, lower the other end of the chain into the cup until DW is
achieved.  The added weight is given by the weight of the length of chain
that has landed in the cup.  This is proportional to the length of that
segment of chain.  You'll have to determine the mass per length of whatever
chain you get, but then taking a weight measurement will be as fast as
measuring the length of chain in the cup against a scale that you draw on a
stick.  Quick and accurate.

Peace,
Sarah

----- Original Message -----
From: "Bill Ballard" <yardbird@vermontel.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, May 10, 2003 9:39 AM
Subject: Re: TR: push/pull dynamometer/Calibrated beam keyweight measure


> At 2:33 PM +0200 5/10/03, Richard Brekne wrote:
> >  >      Hey! Why not a calibrated beam on a pivot, on a
> >>  stand, with sliding weights? As the weights were slid
> >>  along the beam to the correct point, down and upweight
> >>  measurements could be very easily and accurately
> >>  taken. Anyone doing this?
> >  >      Thump
>
> Interesting idea. Yes, David Stanwood's been doing that for ten
> years. It's how he measures FW.
>
> >I dont know, but I think I would sure like to get ahold of one of these
> >things. And I like the idea of automatically being able to pump values
> >into a puter. Nice idea for sure.
>
> Not this puppy, if it's the same one I bought twenty years ago (and
> it appears to be). As far a reading DW/UW, one pushes again a live
> spring (instead of the force being a dead weight). That's fine when
> reading DW. You start at zero spring pressure at the key touch point
> and build up (pressing normal to the key), and at the point when the
> key starts to move the pointer's maximum position is recorded
> mechanically. Any further DW reading really has to start once again
> from dead zero as, once the key starts to move, the friction
> component of the DW is dynamic instead of static. Also if you decide
> to read DW after the key is moving, you must maintain a uniform speed
> with the dynamometer pressing on the key, or the key will
> decelerate/accelerate.
>
> Reading UW is no less tricky. At the point prior to let-off, you
> start with a pressure leass than DW but greater than UW so that the
> key is stopped. You then move upwards slightly with the gauge,
> relieving spring pressure, until the spring pressure hits UW. As with
> DW, once the key is moving certain restrictions apply, the latest
> addition being that upwards motion has to be at a crawl.
>
> It has spent the last twenty years in my shop desk drawer. I prefer a
> dead weight for DW/UW measurements. Far fewer variables affecting the
> reading, than with a live spring.
>
> As far as a continuous stream of numbers into a computer, I'm sure
> state-of-the-art dynamometers exist which will do that. But not this
> one. It's purely mechanical. It lacks a means of translating
> mechanical readings into digital, and a USB port to export them.
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> Reality is the first casualty of technology
>      ...........NPR Commentator Daniel Schorr
> +++++++++++++++++++++
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