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| Gibson Adjustable Bridge Repair - An Alternative Approach http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=51827 |
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| Author: | Woodie G [ Thu Apr 18, 2019 10:22 am ] |
| Post subject: | Gibson Adjustable Bridge Repair - An Alternative Approach |
I hope this is of interest to those doing repair work, as well as those of us with one of those ubiquitous 60's/70's adjustable bridge Gibson wide-waist jumbos, B's, or LG's parked in our closet and needing some attention. If other repair/build shops are like the one where I am serving time, there is a slow but steady stream of Gibson guitars with adjustable bridges that come in the door in need of treatment. For some guitars, that means removal of the bridge and hardware, plugging of the top with related bridge plate work or replacement, and a new fixed-saddle bridge installation. These guitars intonate, play, and sound better with the elimination of the adjustable bridge, whether rosewood or the ceramic/metal saddle version. But sometimes owners want to retain the ability to return to the adjustable bridge configuration, despite a need to address issues such as poor intonation or lack of mid-range mojo, so we use a saddle insert that bolts into the existing captive 6-32 bridge nuts, but can still be configured to fix what is usually a combination of aggressive forward lean in the adjustable saddle and lack of coupling to the soundboard. In the case of this Hummingbird (screw-down pickguard and belly-down adjustable bridge date this to 1969 per Mr. Gruhn), the owner complained of very sharp treble strings and less volume/note-to-note separation than what he was seeing from his other fixed-bridge square shoulder Gibsons. We found that the combination of a very aggressive neck set and years of wear and tear on the bridge hardware caused a very noticable forward roll and lean of the saddle, with E4 15 cents sharp. Attachment: AdjBridge01.jpg Attachment: AdjBridge02.jpg We fabricated the replacement insert from scrap rosewood so as to bed fully in the bottom of the saddle slot/soundboard, used brass #4 washers reamed for the brass 6-32 round-head machine screws to lock the bridge down into intimate contact with the slot. Once fitted, we tweaked the action by removing material from the top edge of the insert, then finished up by setting the intonation points and contouring the upper part of the saddle. Attachment: AdjBridge03.jpg Attachment: AdjBridge04.jpg Not our preferred repair, but certainly an option where the original configuration must be retained and fully retrofitable, but certain issues must still be addressed. Attachment: AdjBridge05.jpg Notes: The extra shell dots on the bridge are remnants of an earlier pickup system, which the owner opted to leave in place (sans wires trimmed flush at the bridge plate). We installed a K&K Pure after verifying that the revised saddle and bridge system would support a passive bridge plate pickup system with adequate gain. The neck angle on this instrument appears to be a legacy of an overly aggressive neck reset at some point in the past. With that in mind, the option to simply replace the existing insert with a slightly revised version was knocked out of consideration in favor of the bolt-down approach. Bolts certainly loosen over time when holding components which vary in dimension (like the wooden saddle insert), but the nature of this design allows easy inspection and bolt re-torque. |
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| Author: | Chris Pile [ Thu Apr 18, 2019 10:29 am ] |
| Post subject: | Re: Gibson Adjustable Bridge Repair - An Alternative Approac |
Nicely done! |
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| Author: | Clay S. [ Thu Apr 18, 2019 11:32 am ] |
| Post subject: | Re: Gibson Adjustable Bridge Repair - An Alternative Approac |
Looks like a workable solution - hard to understand the rational of the original adjustable bridge. When making the insert why didn't you use bone, corian, or one of the other hard plastics? Rosewood doesn't seem like it will be as durable. |
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| Author: | Woodie G [ Thu Apr 18, 2019 11:58 am ] |
| Post subject: | Re: Gibson Adjustable Bridge Repair - An Alternative Approac |
Clay S. wrote: Looks like a workable solution - hard to understand the rational of the original adjustable bridge. When making the insert why didn't you use bone, corian, or one of the other hard plastics? Rosewood doesn't seem like it will be as durable. That is an excellent question, and rest assured that we did offer both solid Corian and a bone insert in rosewood (the saddle is almost 4" long, 0.280 wide, and started with a blank 0.7" tall...we could have ordered the bone, but bone/rosewood was available immediately), but the owner preferred what he felt was the 'woodier' tone of the rosewood saddle...in the past, he had owned one of the ceramic/metal adjustable saddles on another instrument, and did not care for what he considered to be a harsher tone. Keeping a string-on-rosewood saddle was actually a primary consideration for him, despite our concerns with wear, loss of some higher frequency, etc. For my part, this was an exercise in creative problem solving...the boss gave me some limitations and constraints, but did not describe a solution. The final result was a blend of my approach (essentially, just a deeper version of the Gibson saddle resting on the bottom of the existing saddle slot, with an angled, raised rib versus the straight one on the prototype) and some pragmatism on the boss's part re: the labor costs of that approach (the angled, blended top contour was judged to take less time than the raised rib) to keep the repair on budget. |
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