Here is an interesting project recently taken in by the workshop: a Gibson LG-O made in 1966
This is an all Mahogany guitar: Mahogany soundboard, back, ribs and neck. This guitar was a budget instrument at the time of manufacture and sold at an affordable price as an entry-level model. The guitar has a slim neck which measures 1 9/16’’ at the nut and joins the body at the 14th fret.
In 1962 with many thousands of the LG-O sold Gibson decided to exchange the standard rectangular Rosewood bridge for a plastic “belly above” type. This plastic moulded version was held in place by 4 screws that attached from under the soundboard up into the base of the bridge. This was done for ease of removal when dealing with replacements. This was upgraded in 1968 with a Rosewood replacement which included an adjustable saddle.
The soundboard is ladder-braced with 5 lateral braces across its width. This type of bracing gives a distinctive tone that is indicative of the old acoustic Blues sounds of the 1930s. However, this system lacks structural strength and over time the soundboard can become bulged and distorted with string tension. The over large bridge-plate can exasperate the problem as these where generally made of softwood which also offered little structural strength. The LG-O was discontinued in 1974.
Our Brief in this instance was to remove the internal ladder bracing, replace with a scalloped X brace system to give the guitar a more balanced tone and to accentuate the bass tone.
To upgrade the bridge-plate and to make and fit a Rosewood replacement bridge.
Removing the Back
In order to gain easy access to the internal bracing it will be necessary to remove the back.
This LG-O does not have an edge binding around its back outline. Therefore, a thin pallet knife is slipped between the back and the end block to start the separation. Once started a Japanese saw is used to precisely cut through the inner lining. Because of the saw’s thin blade and unique cutting motion very little material is lost during this process.
Once the back is removed the simplistic ladder-brace system is revealed. You will notice that a brace and the bridge-plate are missing. I believe these became loose and subsequently lost years before. Their footprints are still visible.
The remaining braces are easily removed and the internal face of the soundboard is prepped in readiness for its upgrade. An Indian Rosewood bridge-plate is made up and fitted. Rosewood is the workshop’s prefered material for bridge-plate replacement because of its strength to thickness ratio.
Go-bars are a very handy and simple way to fit bridge-plates and braces. They are made from flexible timbers that allows pressure to be applied where needed whilst glue is drying.
The Bracing System
The bracing system is made up and glued into place piece by piece.
Each brace is made from 1/4 sawn straight-grained spruce individually scalloped.
Gluing the Back
Once the bracing system is completed the back is cleaned up and glued into place
A replica of the plastic bridge is made up out of Brazilian Rosewood and fitted
The frets are showing some wear. They are honed and re-profiled and the truss-rod is adjusted.
The guitar is strung up and tested.
I’m happy to report that the finished upgrade turned out very well. The guitar has a sweet sound with a good balance. It has a warmth and depth to the bass with sweet mids and trebles. It likes to be picked as well as strummed and I suspect that it will record very nicely and with a small body guitar that’s all you can really ask for.
Full size photos available here on Flickr