Bill and list, In an earlier post I wrote: >The key ratio alone will tell us practically nothing about the >performance of an action. The hammer/key front ratio is the factor >which will give an indication of the way in which an action is >likely to perform. At 10:30 PM -0400 19/10/00, Bill Ballard wrote: >Agreed. My point however was not quite so concrete. It was just to >say that with .52-3 KRs, his SWs still needed to be pretty good to >avoid high FWs. Already the BWs are in the mild mid-30s. What we >need to know now is what the FWs are that will tell if what is being >balanced @ 35g BW is a serious (or slight mismatch) of SWs and SBRs, >or whether it's a naturally mild-feeling action, ie. well hung. >(The acronyms have been introduced earlier in this thread. What, you >weren't paying attention?) I confess Bill, I must get up to speed with 'acronym speak'. While I understand the forces at work in an action, I've basically worked this stuff through from my own research while designing my own action last year. I realise that much work has been by David Stanwood and others, which has resulted in new definitions and terms. However, I'll promise to widen my piano tech vocab' to include the acronyms ASAP. In my earlier post also I included; >The following link will take you to a drawing on my website, showing >the measurement points we use to determine the hammer/key ratio. > http://www.overspianos.com.au/anrt.jpeg >Hammer/key ratio = (B/A)*(D/C)*(E/F) Bill continued; >Very nice graphic. You're still defining the problem in the linear. >What we're selling to the pianist is not linear but but in the >dimension of mass and weight (more specifically, inertial and >gravitational forces). At what point do you move from adjusting >length to adjusting weight? I presume you are referring to the relationship between leverage ratios and arc relationships (and the way in which we might approach design solutions for an action in a dynamic sense, as apposed to the static measurements we might make). While these are separate matters which both influence dynamic performance, when designing and action, I would consider the arc relationship as a first consideration, since the overall layout of the action will determine the arc relationships. Nonetheless, leverage ratios must also be factored in to allow the final design to function efficiently with the desired key dip and hammer blow distance. >To my knowledge there's only one shank which will achieve [an >optimal relationship to the line-of-centres] and that's the aeolean >shank of the '20s, in which reducing the knuckle to the one quadrant >of it actually used by the jack, cut the height of the standard >knuckle by 1/2. I should like to see a jpeg of this action if anybody has one (please send to ron@overspianos.com.au). Actually, the shank on the new Overs grand piano action (patent application No. PQ6216, March 14 2000) also achieves an optimum arc leverage relationship. You will find a drawing of our action (at rest and in check) at; http://www.overspianos.com.au/actn.jpeg >Fabulous website, BTW. Would you care to talk about the Overs >Modified Grand Action? Modification of existing actions was undertaken (during the course of rebuilds) prior to making a decision (June 1999) to design our own action. The jack/roller contact of the Overs action lies 3.5 mm below the line of centers at rest and 3.5 mm above at let off. We have just produced our first grand piano (a 225cm grand) incorporating the first full action, which has a friction weight of just 5 grams. With a down weight of 50gm and an up weight of 40, this action is very fast and its overall efficiency allows a pianist to play fff with a minimum of effort (yes it still plays reliably at ppp). The adjustable wippen assist springs are set to a graded specification prior to weighing off the keyboard (in the prototype - 18g at the face of the jack of A1 reducing evenly to zero at A#50). The assist spring pressure must be evenly graded (along with the hammer weights and other action components) prior to weighing off the keyboard. Key weights were used to firstly to balance the key stick inertia deviation between the black and white keys, and secondly to achieve the desired down weight. The optimisation of the arc relationships of all action levers and spring arms was accounted for during the design of the Overs action. Hence the repetition lever spring is a completely new design, which is attached to the repetition lever with the lower arm aligned to the line-of-centers between the repetition lever and jack centers. The repetition lever center has been positioned to optimise the arc relationship between the repetition lever and the roller during the hammer's rise out of check. This, combined with the improved repetition lever spring, allows the repetition lever to lift the hammer out of check at the desired speed with approximately 25% less spring load, when compared to that required with a typical double wing spring wippen. The spring efficiencies of this action also play a small part in reducing the overall action friction. The wippen heel and capstan has been rearranged to allow the axis of the capstan to lie perpendicular to the line of centers at half key dip (ease of capstan adjustment is quite OK once you get used to it). This minimises the pressure on the heel cloth and the wippen flange center for a slight efficiency improvement. As with the jack/roller contact, the capstan/wippen heel contact lies on the line of centers at half travel between rest and let-off. The drop screw has been relocated to the roller side of the hammer center - this achieves a slight reduction of the rubbing friction between the drop screw and drop screw leather. This was only possible on this action since the roller slot to hammer center distance was increased to 20mm. This change, combined with the reduction of the wippen to jack center distance, from the typical 99mm, to 75mm, facilitated the optimisation of the jack/roller contact with the line of centers. The 20 mm roller distance from the hammer center causes the wippen rotational speed to be increased by approximately 7% with respect to that of the hammer shank. This slighly increases the inertia of the wippen. However, the Overs wippen weighs in at around 18 gm compared to around 22 for a standard 99mm wippen, thereby offsetting this potential disadvantage. The overall hammer/key ratio is set at 5.9/1 (measured at half key dip), with a key dip of 10.25 mm and with a hammer blow distance of 45 mm. This action will eventually be available for retrofit, but we see considerable potential in licencing it to manufacturers. A leading manufacturer will be trialing the action as a Renner replacement in a few months. We will be exhibiting one of our 225 cm grand pianos with this action at Reno next July. I look forward to meeting many of you there. Regards, Ron Overs -- _________________________ Website: http://www.overspianos.com.au Email: ron@overspianos.com.au _________________________
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