The image above shows how we convert back-cut boards into quarter-cut material for bridge caps, using a resaw bandsaw with a tilt table for the conversion process. It is always much better to order the boards back sawn, converting them into quarter cut material.
Below is a diagram showing how a resaw bandsaw is used for the conversion process;
The angle of the tilt table and the position of the fence is set in response to the grain direction and angle of orientation for each board. If you order boards from a sawmill specifying that they are quarter cut, the sawyers will invariably send you stuff which is so poorly cut that it is unsuitable for use as bridge caps. Most sawyers consider any board where the grain is aligned to within 30 degrees of 'perfect' to be quarter cut. This is not good enough for bridge caps or soundboard panels. Furthermore, back-cut boards are easier to source, since the yield of back-cut stock is much higher than when deliberately quarter cutting a log. You can have total control over the orientation of the medullary ray when converting boards from back to quarter-cut yourself. We source boards for conversion which are 300mm wide by 75mm deep. If you have boards which are only 50 mm deep you can still use them, but more scarf joints (1 or 2) will be required when laying out the bridge cap.
For further information on our procedures, I also include a portion of our report to Steinway in 1996, in response to their criticism of my methods of bridge capping and many other matters.
An extract from "A response to STEINWAY & SONS by RON OVERS", 1996.
BRIDGE CAPS REPLACED TO A DEPTH OF 20MM
While some may argue that the alteration of the depth of a bridge cap is a design modification, I would regard such a change to be too insignificant to effect the tonal or performance characteristics of a piano.
When recapping a bridge section, or an entire bridge, I have always removed the top of the bridge to the bottom of the original bridge pin holes, ie. approximately 20mm below the top of the original bridge. While I understand that this will involve the removal of some of the vertically laminated bridge wood on some pianos, I insist that this is necessary to guarantee that the replacement bridge cap is as strong as the original. I understand that it is common practice for bridges to be repaired by replacing only the top of the bridge - the cap only - and plugging the original pin holes in the vertically laminated section. Although a bridge repaired in this way might look original, I am certain that it will not be as strong as the original bridge. I must reserve the right to decide which technique I will use when recapping a bridge. If a client does not agree with my methods, then they are surely free to choose another repairer. Our replacement bridge caps are accurately quarter cut from Hard Rock Maple of 20mm (at least) in depth. Although a 20mm deep replacement bridge cap involves the removal of part of a vertically laminated bridge, it will ensure that the original bridge pin holes are replaced right to the bottom with new wood. We have replaced many bridge caps. To date, we are not aware of any having developed even hair line cracks. We are particular about the way the bridge wood is cut, the drilling and pinning, and finally, the sealing of the new bridge cap with polyurethane sealer. The recapped bridges are sealed over the entire bridge surface with a polyurethane sealer. The graphite slip coat is applied over the polyurethane. I believe many bridges fail in service because, a) the bridge wood is not cut and/or dried correctly, and b) the sealing coat is often incomplete.
All of the bridge pin holes on the ********** Conservatorium Steinway (D) showed signs of elongation. In addition to recapping the two top sections, we replaced the bridge pins of the other sections with oversize pins. I suspect that the piano has been exposed to considerable humidity variations.
Werner Husmann (Steinway-Hamburg head of international sales) 'asked' me at the Gold Coast (piano technicians convention, 1996) about comments I have made concerning piano bridges, and in particular, my comments regarding Steinway bridge caps.
I have repaired many pianos since the late '70s. I have inspected hundreds of pianos to asses their suitability for rebuilding and prepared pianos for concerts and recordings since the late seventies. It became clear to me, early in my career, that the way in which timber is cut for bridges or bridge caps influences significantly the reliability of the bridge throughout the life of the piano. I noticed that the early Steinway pianos (from around 1900 and earlier), almost without exception, had bridges made from perfectly quarter cut wood. The incidence of failure of those bridges is rare indeed.
The orientation of the medullary ray is, in my view, the important issue relating to the way wood is cut for bridge capping. If the wood is quarter cut, the medullary ray will run parallel to the top face of the bridge. Conversely, if the wood is back cut, the medullary ray will run perpendicular to the face of the bridge cap, and parallel to the sides of the bridge. When the medullary rays run parallel to the edge of a bridge, they will be oriented practically in line with the direction of the bridge pins, into the top face of the bridge cap. In this direction, they offer little support to the bridge pins. It is therefore, more likely that the bridge wood will split adjacent to the bridge pin holes when the wood is back cut. Similarly, there will be a greater tendency for the bridge pin holes to elongate in response to the horizontal string vector forces on the bridge pins, causing the bridge pins to loosen, and tone duration to shorten. In the case of a quarter cut bridge cap, the medullary rays will be oriented in such a way that they provide genuine support to the bridge pins in a horizontal direction, but perpendicular to the support given by the long grain. We can therefore conclude, that the medullary rays offer excellent support to the bridge pins in a quarter cut bridge cap, and minimum support for the bridge pins in a back cut bridge cap.
Many of the Steinway pianos manufactured throughout the sixties, seventies and eighties did not use fully quarter sawn wood for the bridge caps. Much of the wood used was back sawn or cross sawn. This is, in my view, (unfortunate). . . . . . . . I would hope that Steinway understands that my views have not been formulated in an attempt to give piano manufacturers a difficult time. I am as openly critical of my own work. Rather, I am interested in manufacturers (and ourselves) adopting improved (or in some cases reverting back to old) methods where applicable, to improve the reliability of pianos produced. I have come to admire the way in which the Steinway pianos manufactured around the turn of the century, almost without exception, had bridge caps made from perfectly quarter sawn wood. I believe that this factor alone, has been largely responsible for the longevity of their bridges. Similarly, Yamaha bridge caps are, almost without exception, made of quarter cut wood, and their bridges rarely fail. However, many modern piano manufacturers are quite careless about their selection of bridge wood. For example, one Japanese maker seem deliberately to select their bridge material from back cut stock (many other manufacturers from Asia do this also). A couple of years ago I discussed this matter with their Australian office. The factory was allegedly informed of my concerns, but their pianos still leave the factory with back cut bridge caps. Recently I contacted them again in an attempt to bring this matter to their attention. A representative has agreed to come to our workshop for discussions. Recently, I inspected a new ***** *** on the showroom floor, with back-cut bridges which had quite obvious splits. A couple of years ago I observed a new Steinway model B with exactly the same problem at ****** Sydney showroom. I believe these problems can be overcome very simply if the matter is given the attention it deserves.
In our own business, we previously had considerable trouble with supplies of American maple when we specified that it be quarter cut - near enough is not good enough for piano bridges. In recent years, we have been buying our American Maple as back cut boards 300mm wide, and 75mm deep. We resaw these boards on our tilt-table bandsaw to obtain accurately quarter sawn material for our bridge capping requirements, see diagram below;
Selecting quarter cut material for bridge caps.
Although I have discussed the selection of quarter cut bridge wood for bridge caps elsewhere in this document, I understand that Steinway is concerned about statements I am alleged to have made, regarding the reliability of piano bridges. I would like to submit my long held views on these matters. It has been my experience that piano bridges manufactured from back sawn (or cross sawn) wood are much more prone to mechanical failure than bridges manufactured from quarter sawn wood. I have not said, as has been reported, that all back cut bridges fail, or that quarter cut bridges never fail. One need only observe examples of pianos manufactured all over the world, to realise that the real situation is not so 'black and white'. However, the failure rate of back cut bridges is very much greater than that of quarter cut bridges. Therefore I have said, and will continue to say, that it is good piano production (and rebuilding) practice to ensure that bridges are, without exception, manufactured from selected quarter cut wood. A couple of years ago, I was called to inspect a Japanese grand piano which was reported to have tonal problems and tuning instability in the treble region. On inspection, (in addition to the fact that the piano was inexpertly tuned) I found that the long bridge cap was made of two pieces of wood, joined with a typical scarf joint. The wood used for the treble part of the cap was perfectly back sawn, while that used for the tenor part was perfectly quarter cut. In this situation, both ends of the long bridge cap (quarter cut and back cut halves) had been exposed to the same climatic conditions since new. This piano was, to me, an interesting case study of the effect of the selection of bridge wood. The back sawn section had many small splits adjacent to the bridge pins, and the holes were showing significant signs of elongation (due to the side-angle force of the piano wire on the bridge pins), while the quarter sawn section remained in excellent condition, with no sign of deterioration whatever. Interestingly, the tone of back cut bridge section was very poor, whereas the tone of the quarter sawn section was fine.
End of extract
Photogallery of six images - Bridge cap replacement of the Steinway D mentioned in the extract.
As a postscript to the above extract, of the new Steinway pianos I have inspected since 1996, all have had bridge caps which were reasonably-accurately quarter cut. This apparent change in their selection criterion appears to have coincided with their decision to discontinue using European Boxwood as a bridge capping material for the treble sections.
At this time, Yamaha still remains as the only manufacturer from Asia with an understanding of how to cut bridge cap wood correctly. All of the remainder, including Kawai, are using back cut wood for bridge caps. I will update this postscript, should this situation change in the near future.
Ron E. Overs
7 March, 2000