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Gibson B-25 Bridge Plate Replacement

1.0 vintage gibson acoustic b 25 plastic bridge ceramic saddle.jpg 1.1 1963 gibson b 25 bridge plate replacement.jpg
1. Gibson’s Plastic Bridge , featured on many of their early 1960’s flat tops, sports an adjustable, ceramic saddle and is affixed to the top of the guitar by 4 screws. 2. The Bridge Plate supports both the bridge and the adjustable saddle. See all of the related hardware? Because the 170 or so pounds of string tension is concentrated only at the points where the hardware makes contact with the bridge plate, the bridge plate is showing some serious warping. In one spot it’s even coming loose from the top. A more conventional solid maple bridge plate with a glued wooden bridge and drop in saddle will help evenly spread the string tension and, thus, 1) reverse the the damage to the top and 2) stabalize the structural integrity of this guitar for many years to come.
1.2 1963 gibson b 25 bridge plate replacement tools.jpg 1.3 1963 gibson b 25 bridge plate replacement heat soften glue.jpg
3. Tools For Removing a Bridge Plate include a deep throught c-clamp with attached heating iron, an outside clamping caul and a hook-shaped chisel. 4. Heating Things Up. The old glue used by the factory to glue the bridge plate to the top is brittle. Even so, I’m further weakening the glue by heating it up. I heated the iron up to 300 degrees fahrenheit. As I wait for the heat to soften the glue, I frequently loosen the clamp and remove the caul to make sure the finish on the outside of the guitar isn’t sustaining heat damage. Lightly dampening the bridge plate prior to heating further expedites the weakening of the old glue joint.
1.4 1963 gibson b 25 bridge plate removal.jpg 1.5 1963 gibson b 25 bridge plate replacement.jpg
5. Removing the Bridge Plate with a hook shaped chisel only takes a couple of minutes since the heat has weakened the glue joint. Typically I’ll break the bridge plate into 2 or 3 pieces as I remove it. However, this bridge plate is made out of plywood so it will have to come out all at once. 6. With the Bridge Plate Removed you can see the old glue line. As is typical, this bridge plate came out clean without any damage to the top.
1.6 1963 gibson b 25 bridge plate replacement.jpg 1.9 1963 gibson b 25 bridge plate replacement plug layout.jpg
7. A Clean Extraction as evidenced by the presence of only paper thin spruce fibers from the top. Now I’ll plug all of those unnecessary holes in the top. 8. Laying Out the Plugs for the adjustable saddle mounting holes. I’m using the adjustable saddle bolts’ inserts as a template for the spruce plugs.
2.0 1963 gibson b 25 bridge plate replacement cutting plugs.jpg 2.1 1963 gibson b 25 bridge plate replacement repair holes in top.jpg
9. Cutting the Plugs with a jewler’s saw is a snap when used in conjunction with the shop’s pearl cutting work- board. 10. 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.
2.2 1963 gibson b 25 bridge plate replacement bridge saver.jpg 2.3 1963 gibson b 25 bridge plate replacement.jpg
11. The Bridge Saver tool is meant for 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 fore-most bridge screw mounting hole? 12. 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.
2.4 1963 gibson b 25 bridge plate replacement clamp plugs.jpg 2.5 1963 gibson b 25 bridge plate replacement cut plugs flush.jpg
13. 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. 14. 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.

 

2.6 1963 gibson b 25 bridge plate replacement bridge plate blanks.jpg 2.7 1963 gibson b 25 bridge plate replacement thickness sand bridge plate.jpg
15. Selecting a Bridge Plate Blank of appropriate rough size is always possible since we have so many of them tucked away. 16. Thickness Sanding the bridge plate with the luthier’s friend precision sanding station saves me a bunch of time because I only need hand tools for final shaping and fitting. This tool also saves materials as I was able to cross cut the ends of our bridge plate blanks at a 45 degree angle from a resawn maple plank. If I used the old method of hand planing the bridge plate to thickness, the cross cuts would have had to be done at a 90 degree angle in order to provide our bench dog with adequate stabalization power during thicknessing. I’ve set up the station to sand the blank to a thickness of .115″.
2.8 1963 gibson b 25 bridge plate replacement shape bridge plate.jpg 2.9 1963 gibson b 25 bridge plate replacement shape bridge plate block plane.jpg
17. Shaping the Bridge Plate. I want the new bridge plate to help flatten out the top for structural purposes, but I don’t want to force the top so flat that the guitar’s tone suffers. The solution is to arch the gluing surface of the new bridge plate by using a 28′ radiused hollow form as a sanding block. 18. Planing the Bridge Plate where the hollow form left abrassive marks speeds things along. I’ll go back and forth between sanding with the hollow form and making conservative cuts with a block plane until the bridge plate’s gluing surface exhibits an even radius. Stanley’s old model #102 and #103 block planes work particularly well for this task.
3.0 1963 gibson b 25 bridge plate replacement.jpg 3.2 1963 gibson b 25 bridge plate replacement new bridge plate.jpg
19. Scraping the Bridge Plate with a scraper, or in this case, a razor blade with a burr, gets rid of any loose bits of sanding grit and smoothes the finish of the maple. This will help the hide glue I’ll be using to make a stronger bond between the top and the bridge plate. This bridge plate ranges in thickness from .090″ at the outer most ends to .099″ in the center. A good thickness for a flat, even thicknessed bridge plate on a guitar without a warped top would be 3/32″ or .093″. 20. Final Shaping of the Bridge Plate is quick. I used the original bridge plate to layout the new bridge plate by simply tracing the old. At this time in the process I will alter the layout when necessary by adding or removing mass depending upon the particular instrument’s needs. I sand away waste material with a bench-top disc sander, then clean up the edges to the layout lines with a block plane. When the bridge plate’s footprint is established I’ll bevel the bridge plate’s sides where they do not meet up with the cross braces. I use a chisel and a block plane for beveling.
3.3 1963 gibson b 25 bridge plate replacement prepare top.jpg 3.4 1963 gibson b 25 bridge plate replacement hide glue.jpg
21. Preparing the Top for Gluing. I’m getting rid of the remaining old glue and sanding the plugs flush with the top at the same time. A magnet inside the guitar with fine grit self adhesive sandpaper attached does the work while I drive it with magnets outside of the guitar. Plexi-glass is a good material for protecting the instrument’s finish during this process. As with the bridge plate, I’ll very lightly scrape the inside gluing surface of the top in preparation for hide glue, then wipe it clean with some naptha. 22. Gluing the New Bridge Plate with hot hide glue will insure a solid glue joint for some time to come. The inner caul was made from scrap hardwood cut from a tracing of the new bridge plate. I then glued a layer of thin rubberized cork to the caul in order to further insure even clamping pressure.
3.5 1963 gibson b 25 bridge plate replacement drill pin holes.jpg 3.6 1963 gibson b 25 bridge plate replacement ream pin holes.jpg
23. Drilling the Pin Holes must be done with a sacrificial backing block clamped to the bridge plate to prevent tear-out. 24. Reaming the Pin Holes ensures a snug fit for this guitar’s new bridge pins.
3.7 1963 gibson b 25 bridge plate replacement notch pin holes.jpg 3.8 1963 gibson b 25 new bridge plate.jpg
25. Notching the Pin Holes for the strings is done with a small saw. 26. A New Bridge Plate has stabalized the top of this vintage Gibson. In conjunction with a new, more traditional glued wooden bridge and drop in bone saddle, this guitar actually sounds substantially better than it did the day it came into the shop.