The problem is that if you don't understand what it is you are trying to accomplish with placing bridge pin holes and spacings you can end up making a bad copy of possibly a bad layout to begin with. I see a lot of bad bridge layouts mostly from trying to make copies of old bridge pin placements and then just missing by a millimeter or two front or rear and ending up with either way to much side bearing or none at all. Layout it out from scratch isn't difficult. You can mess up making a pattern just as easy as you can mess up doing it from scratch. For those not familiar with the process it goes something like this: 1. Choose a reference hole on the agraffe, right or left it doesn't matter, I use the treble side hole. Stretch a string through your reference hole an pull it tight toward its hitch pin. 2. Where the string crosses the bridge draw a line along side of it (heavy fishing line works fine). That's your reference line for that note. Go to the next note (not unison) one and do the same until you have all the lines drawn for each note 3. Check the spacing to see that it's equal between the lines. Remember that there's another line to go next to it for the other bichord and notice that the spacing between where the bichords and the monochords begin will be a bit different. 4. Measure the spacing between (right to left not front to back yet) the old set of bichord holes. 5. Using a clear ruler draw a line parallel to the first one you drew for the other string in the bichord pair. 6. Visually check the spacing again and correct if necessary. Look at the old bridge cap and see if it roughly matches the spacing there. 7. Measure the front to back spacing on the original and duplicate it roughly or just use 18 mm. Drawing a line connecting the bichord lines (looks kind of like a tic-tac-toe diagram now except for the monochords). Center the front to back spacing on the bridge body. Check it visually. 8. Where those line cross each other is where the bridge pins will go angled appropriately. One note of caution before you set the holes, be sure that there isn't a set of adjacent strings where the front holes of one note will be exactly adjacent to the rear holes of the adjacent note such that the opposite leaning bridge pins will hit each other. If there are some of those then adjust your rear spacing to accommodate. 9. Using sharp punch or an awl punch small starter holes for the drill to use as a guide. They should by punched exactly on the line representing the string line. You don't need to offset them, the diameter of the bridge pins will do that for you. 10. Drill the holes at 20 degrees. 11. Notch or bevel the bridge as you choose. 12. Coat bridge and notches with clear sealer. 13. When the sealer is dry lightly sand bridge top to smooth out sealer with 400 paper. 14. Insert bridge pins (I use #9 pins in the bass section) 15. Put a single drop of thin CA clue where the pin meets the bridge to seal and tighten the pin. 16. Shoot bridge top (and sides) with a few light coats of clear lacquer. Use an aerosol delivery with a fine mist. You don't want a super heavy coat. Three light applications will do. 17. String her up and you're off to the races. Note: You can skip step 5 if you have one of those two hole set punches from Mazzaglia (if you don't and do bridges they have a lot of excellent tools just for this purpose www.geocities.com/mazzaglia_tools) that give you the spacing without having to draw in the second line although the first time it's probably not a bad idea to draw the line in just so you can visualize the front to back spacing and make sure it's centered on the bridge. Remember that on a curved bridge if you center the left hand string, the right one won't be centered. The trick is as you look down on top of a bichord with four bridge pins, you want to compare the distance to the bridge edge between the top left bridge pin and the bottom right one or the top right and the bottom left. Those distances need to be equal. Measure twice, cut once. Check everything visually and label and number each unison in pencil on the bridge to as you go (you'll sand off the numbers before you put the sealer on the bridge) . Check it again and then one more time before you start punching holes. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Joseph Garrett Sent: Sunday, May 31, 2009 7:11 PM To: pianotech Subject: [pianotech] Repairing Bridge David Said: " Sounds good but I would probably not try and make a pattern from that old cap. Just lay it out from scratch. Not hard." Having capped several hundred bridges in the last 35+ years, I consider that to be bad advice to someone who is attempting their first bridge recap. If one is well versed in bridges, etc. it is fine and can be implimented w/o a pattern. However, that is not the case. A rubbing is adviseable. Use the pencil point to locate all of the bridge pin holes, even on the cracked side this is possible. I usually tape the butcher paper to the bridge while I'm doing the rubbing. W/O a pattern of some sort, all kinds of errors can happen. DAMHIK! The idea is to replicate the original bridge, but hopefully improve on it, if possible. Most Uprights had really crappy wood used in the bass bridges. Why? I have no idea, but such is the case. As for the Airplane Plywood, you could google a search and will come up with a whole bucket of sources. Most Aircraft plywood is made of maple with a poplar core. This is more than adequate for recapping. Using delignet is overkill in my opinion. And, it is harder to work with than the Aircraft ply. Regards, Joe Garrett, R.P.T. (Oregon) Captain, Tool Police Squares R I -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20090531/86405c26/attachment-0001.htm>
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