At 9:07 AM -0800 11/11/01, David Love wrote:
>Bill:I may not have stated my question clearly. I was wondering
>about preferred
>flange center to knuckle core distance (16mm, 17mm?) that you combine with
>.51 key ratio. Do you have a preference and let the SWR fall where it will
>making adjustments by altering the hammer weight? Or do you vary your
>selection of the knuckle radius depending on the overall leverage of the
>system and the hammer weight.
No, I don't have a preference which is based on knuckle mounting
distance. How that fits into my "hanging" of the action is minimal. I
just figure that any hammer set can be pushed only so far towards an
envisioned SW curve, so if a given set of hammers is committed to a
particular action, the the SW curve is going to fall in a certain
workable range. Those of you who do this stuff know what workable
means.
Thus Strike Weights are a starting point, a given. The Front Weights
are the end point. How one draws the line from start to finish is
proprietary but it means various contact points in the action will
have to move to produce the particular SWR which will allow the SWs
to be counterbalance with comfortable FWs (which, remember, are a
good representation of the level of inertia in the action) at an
acceptable balance weight.
But in the effort to properly balance (or hang) a set of SWs, both
the key and the hammershank need to pitch in. Which is why, unless I
have good reason not to (and that does happen) I simply assume that
the business of properly hanging that action will be a lot easier if
I start out with 17mm knuckle mounting distances.
>The reason I ask is that I have found a trend in combinations of KR and
>knuckle radii. Depending on choice of hammer weight (a factor not to be
>glossed over lightly) it would seem that a 16mm knuckle works with KR's up
>to .50; 16.5mm up to .52 - .53; 17mm up to .55, 18mm up to .60 or so. (I
>realize that there is also the wippen lever to consider as well which will
>change as the KR changes.)
Six of one , half dozen of the other. A shorter knuckle mounting
distance asks for a lower key ratio, and via versa. No surprise here.
>The knuckle radius doesn't seem to really have a place in the Stanwood
>formulas: R = (BW + FW - (KR x WW)) / SW can be manipulated algebraically
>to isolate different variables. But the knuckle radius remains out of the
>formula loop except to the extent that it impacts BW and therefore will
>change R (Strike weight Ratio).
You're right, and if you look at anyone's model, you're sure to find
something left out. Consider this. Suppose you replace a 16mm/10mm
(mountingdistance/knuckle dia.) with a 17mm/11mm shank. The knuckle
has moved away from the shank center by 1mm, thus reducing its
ability to amplify the SWs, but it has also grown taller by 1mm,
driving the jack-knuckle contact point even lower from level. (This
is the issue which Ron Overs so neatly dispatched with his action
design.) Taking a shank at level, moving the knuckle 1mm out will
reduce its overall leverage. The extra height of the knuckle will
certainly make the shank leverage shrink just a bit more, and we
should be thankful for this. But dropping the shank down from level
to its normal point of rest above the bumper felts, the knuckle
contact point is pushed even further down from level and further into
the neighborhood where rotation produces horizontal motion (friction)
instead of vertical (payload lift).
It gets comlicated and there are more trde-offs than any of us care to admit.
>His formula also does not address distance leverages, that I can see, except
>to the extent that a certain range of SWR's will result in acceptable
>regulation perimeters.
You got that right. The actions's leverage is not being measured by
distance but by weight.
>Do you, when setting up an action, aim for a
>particular distance leverage, i.e. a range of dip/blow combinations, force
>leverage, or both?
If you want to look at it from that angle, then calculating the
lowest SWR is easy. Measured the highest you can raise the hammerline
and still slide the action in and out. Measure the deepest dip you
can lay in without setting the sharps too unreasonably high above the
naturals. That's the lowest overall leverage ratio which will allow
for a reasonable regulation of the action. Remember, this is a
measure of the action based on distance.
>Where do you prefer to take your compromises from? For
>example, if you want to put on a very heavy hammer and don't want to use
>assist springs, you can achieve an acceptable front weight within a range of
>SWR's. But depending on the SWR chosen, your regulation specs will vary
>somewhat.
Why would I want to put on a heavy set of hammers which required
amounts of front weight which really should be balanced by assist
springs (to avoid the inevitably excessive FWs), and then not choose
the help of rep assist springs.
>Personally, I try to set my FW's below maximum by 10-15%, and
>select KR/knuckle radius combinations that give me a .390 - .400 key dip
>with normal blow distance. The resulting SWR will dictate the SW zone.
I don't let SWR dictate the SW zone. I let the set of hammers set
the SW zone. Then, instead of letting the specification of ".390 -
.400 key dip with normal blow distance" (really, the specification
for a particular SWR) dictate the SW, I let the SW and FW curves
dictate the SWR. We're agreed that the FW curve should be specified
(in your case, from the Smart Chart, I presume, and in David
Stanwood's case, something proprietary.) We probably also agree that
there should be a sweet spot for the SWR. For my part, I'm not happy
to go below a 5.5 SWR. If the combination of SW/FW curve asks that
SWR drives below that, I let the Balance Weight float upwards, and
when that gets out of range, I put assist spring reps into the
equation.
But this example assumed a set of hammers which were rhinoceros sized
and excluded the option of spring balancing.
>It's not always possible to do that, sometimes the hammer of choice forces a
>compromise somewhere. Maybe the more precise question is do you find that
>SWR always has a direct relationship to distance leverage and, if so, is
>there a preferred SWR?
Sure there is a preferred SWR, I've stated mine. As far as a direct
relationship between SWR (weight based) and distance based leverage,
there may be. But my model for distance based action leverage would
have to include the losses in pure lift due to the inclination of
levers. I admire any who has built their own spreadsheet models, but
when I build mine, it will clean up this slight inaccuracy. A
customer of mine has an engineering degree from MIT and has just
retired up here to teaching math and physics at his old prep school.
I described this problem of tracking the ratio of horizontal and
vertical vectors of contact points between levers, and he said,
"Piece of cake, the motion of cams." If I didn't have to tune pianos
to pay bills, I'd take off a Friday afternoon and put together a
model with him. He's ready.
But as to a clear relationship between the weight and distance based
readings of action leverage, I'm assuming that they'll be there, I
can't guarantee as to how straightforward that relationship will be.
Bill Ballard RPT
NH Chapter, P.T.G.
"I go, two plus like, three is pretty much totally five. Whatever"
...........The new math
+++++++++++++++++++++
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