action ratios

[Richard Brekne]

This has been up several times and is the source of a lot of head scratching me
thinks

The point is that given a simple lever such as a key, the key ratio is exactly
the same for weight, distance, speed or whatever else comes into the picture. It
you have a 0.5 key ratio, the 10 mm key movement at the front will be 5 mm
capstan movement. 10 grams downwards pressure at the front will balance 5 grams
at the capstan,  speed at the capstan will be half  the speed of the front of
the key.

Now its difficult  to imagine that coupling several levers should make any real
difference to this picture. FW and DW together are exactly that which balances
the rest of the action. Removing Friction from the picture then its FW and BW. I
have never been able to see that the Balance Equation should result in any
different ratio then any other way of measureing total action ratio. That there
are apparent differences I have always chalked up to inperfections in how we
measure. And I have always felt that the weight method of measureing is the most
accurate of the most common methods we use. Besides... its faster and easier as
well.

If there is any real difference in overall action ratio and  SW ratio, I have
yet to see anyone even come close to explaining what it is. I would think it
would be of value to get this whole matter cleared up once and for all.

RicB



"David C. Stanwood" wrote:

> Dear Stéphane & Friends,
>
> I see some confusion in the discussion about what ratio is.  This is my
> view: When we talk about touchweight we refer to weight ratios and in this
> regards we refer to strike weight ratio which is the amount of weight, at
> the front of the key, that it takes to balance a gram of weight at the
> hammer.  When we talk about geometry we refer to distance ratios which is
> the distance the hammer moves for a given unit of distance at the front of
> the key.   Stéphane shows an analysis with mixed types, some touchweight
> and some geometry.  One or the other please!
>
> The discussion that we have been having is about strike weight ratios
> unless said otherwise.  The calculation
> of strike weight ratio is found by determining the Top Action Balance
> Weight which is front weight plus balance weight.  It's the total upward
> force at the front of the key from the hammer/shank & wipppen.   From this
> we subtract the Wippen Balance Weight which is the Wippen Radius Weight
> times the Key Weight Ratio.  The result is the Strike Balance Weight or the
> upward force at the front of the key resulting from the weight of just the
> hammer/shank.  Divide this by the strikewt and we have the strike weight
> ratio.

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html