Wednesday, October 28, 2009
After the bridges have been glued and doweled to the new board, the bottom side can be finished. The first operation is to cot the dowels flush with the rib top. Then a radius is cut on the top of the rib using a special hand plane. Following a lot of hand sanding, the edge gluing surfaces are masked and finish is applied. This completes the bottom side, and the board is ready to be installed in the piano. The top will be finished later.
Monday, October 26, 2009
My soundboard press serves two purposes. It is not only a soundboard press, but also a bridge press. Many rebuilders have a separate fixture for gluing bridges, but in my small shop, space is a major issue, so if I can use one fixture for two purposes, I am happy.
I use liquid hide glue for mounting the bridges. It has a long open time (15-20 minutes), and is easily reversible in case the bridge needs to be removed at a later date. I also think hide glue has a very good sound transmission quality, although that is hard to quantify.
A heavy coat of glue is applied to the bridge body only. The bridge is placed on the new board using the locater pins to position it. Several screws are used to hold the bridges in place, and then the board is turned upside down on the bench. Now I use temporary screws in the holes where dowels will later be installed, through the rib and into the bridge. Finally the board is placed on the press, and the area between the ribs are clamped in place with air pressure.
After the board has been in the press for 5-6 hours, the screws in the ribs are removed, and dowels are installed.
Tuesday, October 20, 2009
After the new caps are planed to the desired height, I reinstall the patterns made from the original caps, and mark every pin hole with a pencil mark. I then reinstall the dryfitted bridge and soundboard into the piano, and place the plate in place. This allows me to be sure that I am satisfied with my down bearing and to check the bridge pin locations.
With the bridge back on the bench, I make any adjustments to the pin locations that I feel necessary. A triple pinned punch is used to center punch the pin locations. When all of the holes have been located, I black and lubricate the bridge top. For drilling the pin hole, most technicians choose to do this operation by hand, as the hole must be drilled at a compound angle. I have devised a method of drilling on my drill press, which allows for a more controlled boring.
Notching is probably the most physical job of rebuilding. Chiseling notches in rock had maple take a lot of force. My shoulder still aches several days after completing this job. It is also a rather tedious job, as it is important to evenly split the bridge pin hole in half with the chisel as the trough is formed. Eighty eight notes, two sides to the bridge equals 196 notches.
The final operation is to install the new bridge pins. The pins are filed flat on top as the final step of the process. Now- get ready to permanently glue the bridges to the mew board.
Thursday, October 15, 2009
After the notches are cut in the bridge tops to the height for proper bearing, the remaining wood must be planed and sanded. Since the board and bridges were dry fitted, I can remove them and do the final work on the bench. (Some rebuilders do all this after the bridges and board are glued into the piano. That requires you to be at some very awkward positions, which my body doesn't do any more!)
I start with a power planer. This requires a lot of care as the machine takes off a lot of material in a hurry. I follow that with a small power sander with 60 grit paper. Again care must be taken. It is very easy to end up with a rounded top, rather than the desired flat top on the bridge with this machine. I finally finish with hand sanding, doing 100, 120, 150 and finishing with 220 paper. Again, care must be taken to keep the bridge top flat. I check this with a straight edge while sanding.
When the sanding is completed, I use my indexing holes to locate the patterns that were made earlier, and mark with pencil all the pin locations. Then the bridge is again dry fitted to the board and piano, and the plate installed. Now I can check that I am satisfied with my bearing, and can also check the bridge pin locations.
Monday, October 12, 2009
I continue to work on two projects simultaneously, that being the Baldwin F and the Mason and Hamlin BB. Setting the bearing (determining how much down bearing will be exerted on the bridge surface)is one of the most demanding jobs, as you only get one chance to get it right (although there are ways to fudge it if you aren't satisfied with the final results). How much bearing is needed at various points on the bridge is determined by each rebuilders experience and theory as to what contributes to the tone quality desired. Every rebuilder has his own formula. A simplified explanation of the formula that I follow is that I determine to approximate the amount of downbearing to equal the amount of crown that is present in the soundboard directly below the area of the bridge where the bearing is being set.
The new bridge caps were installed at a thickness greater than necessary. The bearing is set by cutting notches in the cap to the desired finish height of the bridge cap, and then planing the wood surface to that height (thickness) determined by the notch.
To accomplish this, the bridges are dry fit to the soundboard and the soundboard is dry fit to the piano. The plate is then installed on the pinblock and set to it's predetermined height. A string is stretched between the agraffe or V bar and the bearing point on the plate at the rear of the bridge. The bearing on the bridge is determined by the amount of deflection on the string between the front and rear termination points.
I'm sorry that I haven't added anything to the blog for a while. These have been very busy weeks partially because I have taken two long weekends in the interim. One weekend Rosanna and I attended a couples retreat at Roxbury Camp (staying in our cabin) and another weekend we were in Ocean City MD with some of Rosanna's college days friends. On top of that, I have been tuning pianos nearly every day, with little time in the shop. So, now I hope to be back on track with several posts a week.