Frequently Asked Questions Topics: Grand Piano Soundboard Cleaners Hammer Tapering Jig Key Rebushing Soundboard Repair System Grand Piano Soundboard Cleaners Q: Can I wet the soundboard cleaners to clean a very dirty board? A: Not a good idea. They are basically meant to pick up dust only. The best way to clean a heavily stained board is to wet a cloth, such as a wash cloth, with some water and a little mild cleaner such as Murphy's Oil Soap, wring out the excess, then use the soundboard cleaner to push the wash cloth. The soundboard cleaner lets you put good pressure on a wide area of the cloth and work it back and forth over stains. Hammer Tapering Jig Q: What type of blade do I need on my saw? A: The actual tooth design is not too important. A carbide tipped combination or crosscut blade works fine. However, a premium quality blade such as the 60 tooth Woodworker II by Forrest Manufacturing (800-733- 7111) or equivalent will improve performance of any saw whether you are tapering hammers or cutting wood.      Most important is that your blade be sharp and true. If you experience any discoloration of the felt, have the blade sharpened, then true it to the arbor to eliminate any runout (side to side wobble as the blade rotates). Check this by cross-cutting a small board using your saw's miter gauge. Before the cut is quite completed, hold the board still, turn off the saw, and watch the blade as it coasts to a stop. You will easily be able to see any runout by watching for wobble of the blade in the saw cut. Correct by adding thin brass shim stock (available at auto parts stores) between the blade and arbor flange. Q: What type of tablesaw is best for hammer tapering? A: For this job a small tabletop model will work, but is not ideal. Larger saws allow more working space, hence better safety, ahead of the blade for putting hammers in and out of the jig. Look for one with a standard 3/4" wide miter slot, otherwise you will have to make your own guide strip for the tapering jig to fit the narrower slot found on some saws. If budget and space permit, you will find a contractor or cabinet saw more useful for all around use. top of page Key Rebushing  Q: What's the difference between the two caul method and conventional methods? A: With the two caul method, you bush one side of each mortise on a rail, then go back down the rail bushing the second side. While at first this may sound like it would take twice as long, it actually cuts time by half or more, while improving consistency. It does this through efficiency of tool handling and hand motions.      With conventional methods you use both hands to grab the ends of the cloth strip, then hold the ends evenly in one hand while picking up the glue stick with the other, apply  glue to the cloth, then set the stick down. Next you transfer the ends of the cloth into separate hands and position it into the mortise at proper depth. Then, you hold both ends in place with one hand so the other can pick up and insert the bushing caul, then pick up the knife to trim. That's a lot of tool handling just to bush one key! And, it is very difficult to judge proper cloth depth in the mortise when two pieces of cloth are filling it at once.      In contrast, with the two caul method you hold the cloth in one hand only, with about 1 1/2 inches of cloth extended between thumb and forefinger. With the second hand, you apply glue to this exposed length of cloth, set down the glue stick, and pick up a knife. With the knife in the palm of your hand, you can still pick up and insert bushing cauls with the fingers of that hand. You simply lay the cloth across the mortise, pick up an Intermediate Caul, insert it, and slice the cloth. Then immediately move to the second key and repeat the process. Every 6-7 keys you apply more glue to the cloth. When you get to the end of the rail, you remove the Intermediate cauls and repeat the process using the Final Cauls to install the second piece of cloth. It is very easy to maintain consistent cloth depth, and the entire bushing job for both rails typically takes 1 1/2 to 2 hours. See our Tech Tips page for illustrated instructions, and our publication Efficient Key Rebushing for additional details. Q: What is the difference between Single Shouldered and Double Shouldered  bushing cauls? A: The single shouldered cauls are specifically made for the two caul method. Being flat on one side, they can be used for making "flush cut" (no shoulder) balance rail bushings, as most pianos have, by inserting with the flat side toward the cloth you are installing. Q: I already have sets of conventional double shouldered cauls. Can they be used with the two caul method? A: Yes. You can use your existing double shouldered cauls as Finals. To convert to the two caul method, just buy the appropriate Intermediate Cauls to go with them. Q: Do I have to buy complete sets of both Intermediate and Final cauls for each key pin size to use the two caul method? A: Not exactly. Caul sizes are specific to a given key pin size, since the idea is to mold the bushing to an exact fit to the pin. However, you can economize by using only 45 Intermediates for each key pin size, pulling the first ones out and reinserting ahead as you work your way down the rail. (You do need at least 90 Finals to work efficiently since the Finals need to stay in place several hours until the glue hardens to size the bushings.) Also, some sizes do double duty; i.e. the Intermediate for one size of key pin serves as the Final for another in some cases. See the bushing caul size chart for details. Q: How do I know what thickness of bushing cloth to use? A: Proper thickness is determined for each job by testing the dry fit of the cloth in a few mortises using the correct Final Caul as described in Step 2 here. The optimum thickness may be different for each rail as well. You need to have a range of thicknesses on hand to make this test. Q: I notice that after removing the old bushings, the mortises vary in size somewhat and I have to choose an average cloth thickness for all the keys. Is there a way to make the mortises all the same size? A. Yes, after removing the old bushings with steam or soaking (as described in our publication Efficient Key Rebushing and our Tech Tips page) , insert a Mortise Sizing Caul into each mortise while the key wood is still damp. Allow the keys to dry thoroughly and you'll find the mortises are not only evenly sized but very smooth and firm. We manufacture these only for keys with pin sizes of .125" - .133",  .146" and .162". However, you can use our key bushing caul size #4 (or DS-162 caul) as a mortise sizing caul for .087" pin mortises. top of page Soundboard Repair System  Q: I've seen soundboards that cracked again right alongside a shim. Is shimming a good repair? A: Any soundboard can fail if subjected to enough climate stress. However, shim failures are usually due to improper methods. Hand shimming repairs (carving out the crack with a V shaped tool) are subject to failure for several reasons: Such tools actually crush the wood along the sides of the crack, leaving damaged wood at the glue joint. They also do not remove wood adjacent to the crack that has been damaged by the stress that created the crack in the first place. Due to grain irregularities, hand shimming seldom results in a perfectly uniform groove, so you don't get the thin, void free glue line necessary for a high strength joint. Other reasons for failure are the use of epoxy (rather than a water soluble glue, so the glue line fails to expand and contract with the surrounding wood) and improper drying of the soundboard and shim wood prior to repairing. Finally, boards can fail again if the piano is subjected to the same climate stress that damaged it in the first place. A properly installed humidity control system along with care in placement within the home can minimize the chances of future damage. Q: I don't have an air compressor. Can I use an electric tool with your routing system? A: You can use a flexible shaft tool such as a Foredom, as long as it accepts a 1/4" bit. It will work, but has less power than an air tool and runs at lower speed (16,000 rpm versus 20,000+ for an air tool). A compressor will not cost much more than a Foredom tool, and is very useful for spraying, blowing dust from actions, etc. Q: What size compressor would I need? A: A 2.5 to 3 hp compressor is adequate. Air die grinders need a minimum of 90 psi and consume around 4-6 cfm at that pressure. A compressor output of 3-4 cfm @ 90 psi is adequate, since the air tool usage is intermittent, giving the compressor time to catch up between passes. You'll find an article titled, "Choosing a compressor" in the August 2003 issue #164 of Fine Woodworking Magazine, Q: Can I use old soundboard wood for shim stock? A: Not easily. When fitting a shim into a tapered groove, the shim must be taller than the board thickness to allow for fitting and have allowance for trimming flush. Q: Can the shim be colored to match the old soundboard? A: Yes, you can tint the shim slightly using a dye stain sprayed with an air brush. However, you must be very careful not to overdo it. Spray freehand, do not mask the edges of the shim, and apply much less color than you think you need. A shim that looks properly tinted initially will appear as an obvious paint stripe after the final clear coats are on the board. Realize that the new white shim wood will acquire an amber color with time and look much less obvious. See our publication, Router Repair of Soundboard Cracks for full details. top of page
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