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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