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Finger Lakes Guitar Repair
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Gibson B-25 New Bridge

11/24/2008

1.0 gibson b 25 reverse belly plastic bridge upgrade cracked bridge.jpg 1.2 gibson b 25 plastic bridge screws adjustable saddle hardware.jpg
1. Gibson B-25 Adj. The “adj” designates a ceramic saddle which may be “adjusted” via. 2 machine screws located at both ends of the saddle. This guitar also features a plastic bridge. No wonder the in- strument has a significantly bowed top when under string tension. Basically, this bridge is not up to the task of evenly distributing the string tension, as evidenced by the stress crack on the rear of the bridge. 2. From the Interior of the Instrument you can see all of the bridge related hardware. The plastic bridge is held in place by 4 screws that go through the bridge plate and top. The two large nuts accomodate the saddle adjusting screws and the threaded inserts that allow the machine screws to raise and lower the ceramic saddle.
1.3 gibson b 25 plastic bridge replacement layout spruce plug.jpg 1.4 gibson b 25 plastic bridge replacement cut out spruce top plug.jpg
3. Laying Out the Plugs for the adjustable saddle mounting holes. I’m using one of the adjustable saddle’s bolt inserts as a template for the spruce plugs. 4. Cutting the Plugs with a jewler’s saw is a snap when used in conjunction with the shop’s pearl cutting work- board.
1.5 gibson b 25 plastic bridge replacement bridge saver.jpg 1.6 gibson b 25 plastic bridge replacement bridge saver inside guitar.jpg
5. Preparing the Bridge Mounting Screw Holes for Plugging is a straight- forward affair with the help of stew- mac’s bridge-saver. This outer stop and small brass handle allow me to drive the tool from outside of the guitar. 6. The Bridge Saver tool is meant to aid in the repair of a worn bridge plate by hollowing the bridge plate around a worn bridge pin hole in preparation for plugging. It also does a great job of repairing small holes in spruce tops. See the little dome shaped hollow I created around the forward bridge mounting screw hole?
1.7 gibson b 25 plastic bridge replacement bridge saver plug cutter.jpg 1.8 gibson b 25 plastic bridge replacement glue in plugs.jpg
7. Cutting Spruce Plugs with the bridge-saver’s plug cutter on the drill press. This tool quickly fabricates plugs that perfectly correspond to the hollows on the underside of the guitar’s top. 8. Clamping the Plugs as the glue cures with magnets is quick and easy. I always place the outer magnet first, then match up the inner magnet to the outer. This prevents any accidental damage to an instrument’s finish. Further damage prevention is obtained through the use of rubberized cork placed between the outer magnet and the instrument.
1.9 gibson b 25 plastic bridge replacement trim plugs flush.jpg 2.0 gibson b 25 plastic bridge replacement pattern sanding new bridge profile.jpg
9. Trimming the Plugs Flush with the top is best done with a razor sharp chisel. I’m using a cranked neck chisel for this job but a hollow- ground conventional chisel with the bevel resting on the guitar’s top would also work. 10. Pattern Sanding the New Bridge gives the bridge blank its new profile. The Luthier’s sanding station comes with a “robo sander”. This is a drill press driven drum sander that has a bearing. The bearing follows an old bridge with the appropriate profile while the sanding drum removes unwanted ebony from the bridge blank. Both bridges are attached to a squared section of 4″x4 with carpet tape.
2.1 gibson b 25 plastic bridge replacement laying out new bridge foot print.jpg 2.3 gibson b 25 plastic bridge replacement drill out pin holes.jpg
11. Laying Out the New Bridge on an ebony bridge blank. Because the old bridge didn’t leave enough mass behind the bridge pin holes to adequately stabalize the top, I’m making he new bridge 1/16″ wider at the rear of the bridge. 12. Drilling the Bridge Pin Holes with a brad point bit on the drill press. The bridge must be backed by a sac- raficial block to prevent tear-out.
2.4 gibson b 25 plastic bridge replacement new bridge.jpg 2.5 gibson b 25 plastic bridge replacement scoring lacquer.jpg
13. The New Bridge , ready for gluing. 14. Scoring the Lacquer on the top of the guitar in preparation for removal is done with a sharp knife while the bridge is dry clamped in place.
2.6 gibson b 25 plastic bridge replacement darkened lacquer.jpg 2.7 gibson b 25 plastic bridge replacement scraping away finish.jpg
15. The Shadow of the Original Bridge shows us just how little of the original bridge’s footprint extended behind the bridge pin holes. The footprint of the new bridge goes a bit further back (as evidenced by the score mark in the lacquer). 16. Striping the Lacquer from the top where I’ll be gluing the new bridge is necessary to obtain a strong glue joint. A chisel, scraper, or a razor blade with a burr like a scraper, are all usefull tools for this task.
2.8 gibson b 25 plastic bridge replacement glue bridge hide glue.jpg 3.0 gibson b 25 plastic bridge replacement ream pin holes.jpg
17. Gluing the New Bridge is done in the usual manner with hot hide glue, two specialty clamping cauls and a c-clamp. 18. Reaming the Pin Holes will allow for a good bridge pin fit.
3.1 gibson b 25 plastic bridge replacement notch pin holes.jpg 3.2 gibson b 25 plastic bridge replacement layout saddle slot the intonator.jpg
19. Notching the Pin Holes with a small back-saw. 20. Laying Out the Location of the Saddle Slot is pretty easy and very accurate with stew mac’s “the intonator”. This specialty tool is a set of adjustable saddles held in place by the bridge pins. I adjust the saddles individually until each string length exhibits proper intonation. Now I’m marking the location of each saddle.
3.3 gibson b 25 plastic bridge replacement intonation.jpg 3.4 gibson b 25 plastic bridge replacement saddle slot layed out for intonation.jpg
21. Intonating with a Strobe Tuner , or, in this case, Peterson’s virtual strobe tuner called the “strobo- flip” is very accurate. 22. Ready for Routing. Since Gibson, as with most manu- facturers, uses a single saddle, I’ll route the saddle slot as a compromise between the intonation demands of each individual string. When I fab- ricate the new bone saddle I’ll make it compensated to further dial in the intonation.
3.5 gibson b 25 plastic bridge replacement cutting saddle slot.jpg 3.6 gibson b 25 plastic bridge replacement after.jpg
23. Routing the Saddle Slot. I prefer to use a dremel tool with Stew Mac’s saddle slot routing jig and related down-cut bits. 24. A Replacement Bridge. This bridge has an appearance similar to some of the wooden reverse belly bridges that Gibson produced around the same era of this guitar.
3.7 gibson b 25 plastic bridge replacement ebony reverse belly.jpg 3.8 gibson b 25 plastic bridge replacement reverse belly bridge drop in saddle.jpg
25. This New Bridge has sig- nificantly improved the tone and projection of this old Gibson and stabalized the top. 26. A Drop-In Bone Saddle plays a key role in this guitar’s im- proved intonation and tone.
3.8 1963 gibson b 25 new bridge plate.jpg
27. A New Bridge Plate. Here’s a photo of the other half of the repair, a new bridge plate.