John and list, John Hartman wrote: >Since you opened up this can of worms I hope you won't be offended if I >add to the criticism. Your technique for re-capping bridges has the >following problems. Not at all. Similarly, I trust that you will not be offended by my reply. >1 You have weakened the bridge by creating a vertical joint. The end >grain to end grain glue joint has little integrity. There is no doubt that the bridge will be somewhat weakened at the vertical joint between the new cap and the original bridge cap of the adjacent section, but it nonetheless will have sufficient strength if it is properly fitted. The vertical joint must actually be a joint, ie. the adjoining ends of the new cap must be fitted up to the original bridge material. We have done many such recaps with no failures to date. However, I have made this choice against the option which you obviously prefer, which would require filling/plugging the holes in the original bridge prior to recapping with a standard depth cap. While the plugging approach would maintain the original appearance of the bridge, it would not be original. In the body of the bridge it would contain wooden plugs (with the plug long-grain running more or less parallel to the axis of the bridge pins - hardly a scenario you would consider to be ideal for pin support). Alternatively, one could fill the holes with marine grade epoxy. And while this may indeed provide a satisfactory substrate for the new pins (as many repairers have proven), it nevertheless may cause the drill bit to wander somewhat when the new cap and bridge body is drilled for the bridge pins - slightly increasing the risk of elongated pin holes. While many technicians use the epoxy method with success, I have not been prepared to do it up to this time. I am not going to follow your example and state that techniques other than those we employ are wrong. I will be satisfied with leaving such diplomacy to yourself and Steinway (Hamburg). >You have literally >cut the bridge in half. I have not literally cut the bridge in half; 10 to 20 mm, ie. approximately 30 to 50%, of original bridge remains (depending on the original height). >2 The techniques you have used can not be easily reversed. I agree. But thankfully I don't always wish to reverse everything I do, just most of it. Then again, why would anyone need to reverse it unless the new bridge caps were to fail? To date (from 1988), none of our recaps have shown any signs of pin movement (the Hard Maple or local Beech we select has an ADD in excess of 0.7 grams/cc - typically 0.72 to 0.74). I believe poorly selected bridge stock which is inadequately sealed and not quarter cut, is the must common cause of failed bridges. >I usually >don't consider this to be a big deal but in this case the remedy is >going to be quite costly. When the piano is finally restored an entire >new bridge will need to be built. If and when the piano is fully restored, it may require new bridges if the sound board is replaced. And who knows, the repaired bridges might be of sufficient soundness to use again? >3 Your technique adds nothing to the quality of the piano. My technique (at least the little bit we are discussing) is not intended to 'add' nor take away any quality, it is intended as a means of restoring a damaged bridge to a state of bridge-pin 'firmness' which might well allow the piano to speak as its maker originally intended. >Your notion >of having new wood for the pin holes seems, to me, to be misguided. You are entitled to your view, as I also am entitled to mine. >There is nothing wrong with filling the holes in the bridge body with >epoxy prier to re-capping. If this was your reasoning why not build a >new bridge in the same manner as the original? Because I believe that, when the other string sections can be repaired with re-notching and fitting oversize pins, it is a superior repair to replace just the damaged string sections the way we do, as opposed to the alternative of building new caps in the same manner as the original or plugging. I am yet to be convinced that there is any tonal advantage in employing vertically laminated construction for bridges. I regard them as more of a talking feature for salesman to impress potential clients of their piano knowledge, when in reality they might posses but little. >4 Your technique is more elaborate and takes longer than the traditional >method. We would have to compare our respective workshop time sheets to verify your statement, but frankly I don't care terribly even if you are right. It's not necessarily bad to take the more difficult road if there are benefits in doing so. Furthermore, you might be surprised at how quickly we can set up the routing tracks beside the bridge, attaching them to the protective masking tape layer with car body filler. Down bearing alterations, when required, can be factored into the set height of the router tracks, and I would be surprised if removing the additional 10 mm of bridge height costs any more in time to that of plugging or filling with epoxy, the original holes. Mind you, I am not promoting our approach as 'the method'. It is 'a method'. We are satisfied that our technique results in good performing pianos with uniform tone up to and across the transition from the original to new cap material. Other technicians are free to use ours or another method should they prefer. >To recap; you have destroyed the bridge, you have created a new problem >for the future, you have made no improvement and you have wasted time. What about paraphrasing your above words to say, "since Overs is silly enough to have chosen a repair procedure which appears to be not in the great 'tradition' in which I recap bridges, then he must be wrong since I am right"? Perhaps I'm missing something. Has this excellent list suddenly morphed from a technical forum to a Court Marshall? > There is a difference between re-engineering and de-engineering. I agree. However, if you take the trouble to seek an opinion from a structural engineer (as I did in 1996) re the two repair scenarios under discussion, you will find that the engineer will favour the repair method we use with respect to the bridge's holding power of the bridge pins. Of course, I grant that the vertical joint will not be as robust as a scarf joint would be. But it is quite impractical to use a scarf joint between string sections when repairing an original bridge, unless the entire bridge is to be recapped. We manufacture full length caps with 1:5 scarf joints when a full bridge is to be recapped. Yes we could remove the entire bridge to the panel and remanufacture a vertically laminated bridge, but why, when I am yet to be convinced that the tone will suffer with the thicker solid cap? Furthermore, when removing an original bridge down to the sound board panel there is some risk of picking up the grain and/or thinning of the original panel thickness. Machining off the bulk of a bridge and recapping down to 20 mm (to the bottom of the pin holes) makes for a clean and tidy repair which does not appear to suffer from inferior tone. On the contrary, we have found the tonal quality often to be very much improved (which we mostly attribute to the improved pin holding power and more uniform string offset angles of the new cap). But it is always difficult to know which aspects or modifications are responsible for a tonal improvement when a whole raft of alterations are undertaken during a rebuild. Regarding the alleged strength advantage of a vertically laminated bridge, which I expect will come in a subsequent post if I don't mention it now. I have no doubt that a laminated wooden section will exhibit superior strength qualities, ie. a higher modulus of elasticity (ME), when compared to a similar section size manufactured from solid stock, but in one vector only. The increased ME of the laminated piece will be in a direction perpendicular to the face of the laminates, while the ME parallel to the laminates will be substantially unaffected. I put it to you that the ME in the vertical plane (when the bridge is mounted on the sound board panel) is the factor which will have an influence on the sound board's impedance and sustain. Whereas the ME parallel to the sound board panel will be of little importance. Therefore, in the case of the laminated bridge, the increase in ME will be largely in a direction parallel to the sound board panel - deriving little if any acoustical benefit. It is for these reasons that I believe that vertically laminated bridges, which cost much in time and wasted wood to manufacture, would seem to offer little if any improvement in the acoustical performance of the piano. Sincerely, Ron Overs -- Overs Pianos Sydney Australia ________________________ Web site: http://www.overspianos.com.au Email: mailto:ron@overspianos.com.au ________________________
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