In a message dated 10/12/98 3:30:37 PM Central Daylight Time, Stanwood@tiac.net writes: > >BW=(DW + UW)/2...What does that show us? I am not particularly > >up on Stanwood's "balance weight" work. Was there a recent > >article in the Journal I missed? With a 50 gram DW and a 25 > >gram UW we have 37.5 BW which I would assume is a good balance > >weight? With a 60 gram DW and a 30 gram UW we would have a 45 > >gram BW. A 60 DW and 20 UW would be 40 BW. > > > >Thanks in advance... > > > >David ilvedson, RPT > >Pacifica, CA > > David, > > 38 is a good "Normal" BW for modern pianos. > > On the subject of Balance Weight. Friction causes DownWt and UpWt align > themselves around a point in between. As friction is reduced, DownWt and > UpWt converge on this point. As friction is increased they divirge from > this point. The point is: that if there were no friction in the action it > would take one weight to balance the key like a beam balance. That amount > of weight is the balance weight. We can only infer this by measuring > Down/Up and computing BW = (Down+Up)/2; > > Friction Weight is found as (Down-Up)/2. This tells how much weight added > to the Balance Weight it would take to make the key go down (DownWt), and > how much weight taken away from the BW it would take to make the key go up > (UpWt). > > So a key with a 50/20 D/U would have BW/F of 35/20. To change D/U you work > on the BW/F. I personally find it impossible to deal with Up/Down > without using the components of BW/F. > > If anyones in Houston this week? I'll be teaching a workshop: > > "Changing from one Up/Down Weight to another Up/Down Weight" > > > Here is an excerpt from my handout. We are all going to work the weight > and friction on action models to change up/down to our desire: > > Three Steps: > > I. Measure old Up/Down Weight, then calculate old Balance Weight and > Friction Weight. > Pick a New Up/Down Weight, then calculate new Balance Weight and new > Friction Weight > > II. Change the old Balance Weight to the new Balance Weight by adding or > subtracting keyleads, > or by increasing or decreasing support spring tension. > > III. Change the old Friction Weight to the new Friction Weight by adding or > subtracting friction in the > hammer flanges, wippen flanges, or key bushings. > > > When talking about key balancing it is always preferable to talk BW because > it separates out friction as a separate issue. Sorry to get carried away > here but this is an area that most of us can't deal with. I hope to change > that. It's not rocket science, it's seesaw science! > > On the subject of Turbo wips: One mistake that makers make is asking too > much of a wippen support spring. > The highest BW Balance to for use with support spring is 54 grams. > Attaching the spring and achieving a final BW of 35 means the spring is > working 19 grams off the BW. The spring can be adjusted to as low as > 30gram BW for a very light touch, in which case it would be working 24 > grams. This is our red line. > > We almost always use wippen support springs in all our action work. I > think they are great and they are an underutilized resource in piano > making. Piano makers just don't know how to use them the right way. > An exception is the Hamburg Steinways of the 1920's who set spring to > support the weight of the wippen on the bench and then balanced the keys > using Up/Down. Unfortunately there are piano makers out there, some very > good ones, who ask as much as 40 grams or even 50 grams of the support > spring. > > Ed, I agree that hammer weight can be a big problem. So can overall action > ratio and I feel that this an even greater culprit contributing to heavy > actions. In Steinway the big culprit is Key Ratios: they vary all over the > Map! yet this is hardly ever mentioned in discussion of trouble shooting > heavy action. > > David C. Stanwood > All, I have set up a mathematical action model on the handy PC to help me understand this issue of balance weight and friction weight. Basically, by inputting dimensional specs for all the parts I can come up with locations of all points in the action on a two dimensional grid. You input specs and can then vary key dip to see how the locations of each part changes as the key is depressed. I have also added weight information for each part (per David's metrology). With some added calculations, I then have upweight, downweight and whatever other weight you want based on the layout and weight of all the parts. With specs taken from a 1902 S&S O with what looks like original parts, I get calculated DW of 45 and an UW of 36. I am still working on it, but this is not far from the actual DW and UW (in a very loose, old action I should add). Although 45 and 36 are fairly close, the point is that the spread between DW and UW is most certainly not all due to friction. Recall that I said nothing about friction. My model is currently doing without it (I will correct this in the future). The difference is due to the way the parts move on arcs. Weight acts vertically only and the parts are not all moving only vertically. While the spread may get closer, it certainly won't converge on 0 with no friction. David - I believe you have also given examples of how changing a capstan line also corrected "friction." I don't believe this was because it cleared up all the friction at the capstan/heel connection. Having said all this, if calling it all "friction" works -- great. It certainly seems that David is getting results with his system and that is what we are after. It also seems to be something that is fairly easily implemented. I just want to understand it a little better. I read numerous post about knuckle size, spread changes, etc., etc., and lots of speculation about what effect they will have. I think that this is a dangerous game because all of the parts interact in ways you may not expect. I want something that I can change a few numbers and find out the results. David - I will be in your class next week in Houston, I will try to keep my mouth shut and absorb all I can. I think your work is of great value, although my wife wonders what screws you have loosened in my head. I started out trying to "run a few numbers" to help choose parts and have gone off the deep end. Scott Kuhn
This PTG archive page provided courtesy of Moy Piano Service, LLC