Gibson Construction Evolution

 

1918 to 1938

Many interesting changes occurred in the development of the Gibson banjo line between its inception in October 1918, and the end of it’s “pre-war” era in 1938. (For a glimpse at the sequential development, see Chronology of Gibson Banjos.)

Following are details of construction features that occurred during this period:

Model designations: The banjo models were given letter codings to indicate the type of stringing: TB referred to a tenor banjo, PB stood for plectrum banjo, GB described a guitar banjo, MB was applied to a mandolin banjo, UB denoted a ukulele banjo, and RB indicate a regular (5-string) banjo. The letters were followed by a number indicating the grade or quality of the instrument: -00 (double zero) was bottom of the line (although there was a short-lived “Jr.” model which was the least expensive); -0 was next; -1 was slightly better, and usually meant nickel plating and plain-colored finish; -11 (double 1) was a secondary inexpensive version; -2 followed with fancier inlays and extra binding; -3 was fancier; -4 fancier yet; and -5 (for a brief period) was the fanciest model boasting gold plating, choice curly maple, and elaborate inlay designs. Thus a TB-5 was a tenor banjo with -5 grade fancy trimmings.

From 1925 to 1930, several fancy modes made their debut; the style -6 with fancy black-and-white binding (or sometimes gold-speckled binding); the TF or Florentine; the TG or Granada; the Bella Voce (which means “beautiful voice” in Italian); and the All American — an elaborate instrument with a carved eagle on the peghead.

For detailed descriptions of banjo models, see Gibson Banjo Models

Rims: Except for the very first Gibson banjos, all of the rims for this period have been made of steamed, rolled, and laminated maple. Maple was selected for its superior bending qualities compared to other woods in it’s weight/mass class (cherry, oak, etc.) at approx 35-40 pounds per cubic foot.

Rim Construction (1-b) Depending on the model, there were either of three or four plies: three plies of 1/4″ maple to make up a 3/4″ rim machined down for one-piece flange models, and four plies of 1/4″ rim to make up the heavy rim used for tube-and-plate models. All of the laminate ends were taper-cut, a method of angling the joining ends of each laminate so that they would overlap rather than joint flat end-to-end.

The added mass of the fourth ply on tube-and plate rims contributed to the brightness and amplitude of these banjo models.

 

Rim Construction (1-d) To the inexperienced observer, some rims appear to have been made of five thinner plies; but this is a misconception caused by a practice still in use today. The bending and lamination process is a difficult one and several rims might come off the mold with unsightly glue joints. To improve the cosmetic appearance, a poorly glued three-ply rim would be placed on a lathe and a “cut” made into the glue joints. Then, thin filler strips would be glued into the cuts and then machined flush, resulting in a multiply appearance, while still basically a three-ply construction.

One-piece flange models required that the rim be machined down so that the flange could slip over the rim. This resulted in a 9-1/2″ inside diameter and approximately 10-1/4″ outside diameter, and thus the lower portion of the rim had thin walls approx 9/16″ thick. The tube-and-plate models required an added lip to support the tube and did not require machining down of the rim, leaving the tube and plate rims to be a full 3/4″ thick.

Flanges: The tube was the first non-shoe system used by Gibson to secure the tension hooks (that tighten the head). At the first introduction of the full resonator models, a stamped “plate” was added beneath the tube to fill the opening between the rim and the lip of the resonator. This plate had stamped perforations around its surface. At one point, the lesser models had hex-shaped openings in the flange compared to the classic Mastertone arched opening with rounded ends. The first models used small hex-head screws that went through a hold the flange to hold the flange and rim assembly to the resonator. This was later changed to the hex-head screw going through a separate bracket below the flange that was attached to the rim, and still later to a serrated thumbscrew replacing the hex-head screw.

Coordinator rods: One of Gibson’s developments for attaching the neck to the rim was the “coordinator rod” system; two brass rods that attached to two screws in the heel of the banjo neck. The rods secured the neck to the rim and provided a means for correcting the “action” (height of strings above the fretboard). By selectively tightening the nuts at the tailpiece-end of the rods, the angle of the neck could be changed to adjust the neck’s angle. Gibson’s first banjos had a nut on the top neck screw and only one rod on the lower neck screw. The earliest banjos with the double-rod coordinator rod sytem had one lag screw threaded into the neck and one “L”-shaped lag screw embedded into the bottom of the neck’s heel (these were permanently glued in and could never be removed).

Tone chambers: The “tone chamber” was a metallic device that sat on top of the wood rim to enhance the vibrations of the (then) skin head. Several variations were created by Gibson, and these can be followed in the Evolution of Gibson Banjo Rim Assemblies. It has been thought that the spring loaded “ball bearing” tone chamber was designed to counter the effects of weather changes on the skin heads. This is not true, especially since a vertical change in the head’s position would cause improper playing. The springs were employed to improve the resilience (springiness) of the tone chamber. This design feature is attributed to Lloyd Loar.

spring-loaded ball-bearing tone chamber Gibson’s spring-loaded ball-bearing tone chamber system was a marvelous engineering feat of wood and metal parts. The assembly included (left to right) a grooved stretcher band, exterior tone chamber rim, tone tube with integral lip and arched upper ring, tube and plate assembly, 24 ball bearings, 24 coil springs, and 48 flat washers.Each spring was rated at 460 pounds per inch.

 

48 washers Of the 48 washers, 24 were placed below the springs, and 24 were countersunk – to hold the ball and keep it centered – and placed above the washers. Each spring, washer, and ball assembly went into a hole drilled in the rim. To ensure accurate height and contact of the balls to the tone tube, thin paper shims were placed beneath the bottom-most washer and the rim. (The shims are often discarded and rarely found on banjos today, except on those rare banjos that were never disassembled before.)

 

Banjo Rim Assembly With all the springs in place, the rim is finally ready to have the tone tube installed. The assembly of these rims was very time consuming and it is no wonder that the Company eventually favored a one-piece tone chamber and lastly, a one-piece cast flange.


 

The ball-bearing tone chamber was followed by its look alike (from the outside) cast one-piece arch-top tone chamber, and later by the wider active surface of the flat-top tone chamber.

Woods: Each of the model designations indicated a particular species of wood used for that model (see Banjo Model Features, below). The lower numbers indicated that plain maple was used with a colored finish such as “dark mahogany” stain used over maple. Curly maple, burl walnut, and Honduras mahogany were available on their respective models. Other woods such as white holly, were available on fancy models like the Florentine and Bella Voce. In all cases, the rims were made of maple, and the majority of fretboards were made of Brazilian rosewood — not ebony as commonly believed. Only the pre-1925 (trapdoor period) and style -6 banjos had ebony fretboards. Except for the earliest models, all of the banjos made from 1925 to 1935 (in fact, until around 1969) had one-piece necks (however, pegheads were fitted with laminated “ears” to give them the necessary width, and the earliest models had a veneer over the back of the peghead to cover up the ear glue joints).

Banjo serial numbers: During the 1920s, Gibson instruments were made in lots of 40s (for the most part, this procedure continues today). the bins that were used to move instruments from department to department had 40 cubbyholes. An entire bin was a “lot” and would contain instruments of the same model. Sometimes two or three bins or lots of the same model would be made at one time. To assure that parts would fit together and that the finish color would match, the serial number of each banjo was stamped inside its rim, penciled on the neck heel, and chalked or painted in white or red on the inside surface of the resonator (with red numbers most often being painted along the inner edge of the resonator so they could be read through the holes in the plate or flange, yet the red would not be obviously visible).

The number was in two parts: first a four digit number to indicate the factory order number or lot number, and then a second series (usually two digits) to designate that particular banjo within the lot. Banjos made prior to February 1925 were numbered in the 11,000s. With the introduction of the new full-resonator models in February 1925, a new prefix was assigned to the banjo line, beginning with 8,000. Around 1935, when the series reached the 9,900s, it was again changed to a whole variety of numbers whoe dates have been difficult to document or verify. Although each new year did not precisely mark a change in the numbering system, the following chart will serve as a close guide to Gibson’s early serial numbers and their approximate date:

1925…..#8,000 1928…..#8,800 1931…..#9,400 1934…..#9,800
1926…..#8,350 1929…..#9,000 1932…..#9,600 1935…..#9,900
1927…..#8,600 1930…..#9,200 1933…..#9,700 1936…..various

Platings: Instruments were offered in three basic plating finishes; nickel, chrome (them called “chromium”), and gold. The gold plating was often referred to as “triple-gold plating” — a description of the length of time pieces were left in the plating bath (and not an indication that three separate plating processes were done). Some of the gold-plated models were “Florentined,” a burnishing technique that dulled the plated surface to produce a matte background.

Banjo model features:

Several models graced the Gibson banjo line in this period. For detailed information see Banjo model features.

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