Liutaio Mottola Stringed Instrument Design



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Construction Details of the Libellula Electric Upright Bass - Finishing and Final Assembly

In previous pages the construction of the body, wing, and bridge subassembly were outlined. This page describes the finishing and final assembly of the Libellula Electric Upright Bass (EUB).

Last updated: Saturday, August 15, 2015

Once all of the sub assemblies are done they are sanded to 320 grit, with the exception of the scroll and pegbox, which are scraped smooth with a scraper. The instrument is then steel wooled with 0000 grade. Then the body and the wing are given three coats of pure Tung oil. Each coat is wiped on, allowed to soak in for about 15 minutes, and then the excess is wiped off. Any finish desired can be used on this instrument, but the pure Tung oil makes a nice looking and very nice feeling finish for the mahogany. Here the body and the wing (behind the body) are hanging up to dry.

Threaded inserts are installed in the holes along the back of the instrument. The inserts I'm using are driven in with a hex key. The wing attaches to the body using these threaded holes.

A string anchor block is fashioned out of rosewood.


The top surface of the string anchor block has two holes drilled through it to provide access for the bridge action adjustment set screws. It also has four holes drilled to provide access for the string anchor set screws. The string anchors are 3/16” drill bit stop collars. The stop collars are epoxied into the large counter bores.

Shorter threaded inserts are also inserted into holes in the floor of the bridge cavity. Set screws are screwed into these inserts so that they can be adjusted from the back of the instrument. Then the string anchor is screwed onto the back of the instrument using wood screws on the inside of the bridge cavity.

The nut is roughed out in rosewood, but it is not slotted or glued to the pegbox at this time.

Cover plates for the control cavities are fashioned out of PVC.

The insides of the control cavities and the undersides of the cover plates are shielded with conductive foil.

The components are installed in the first control cavity (the one with the volume pot) and it is wired.

The lead wire from the piezo transducer is unfortunately microphonic for a few inches after the connection with the piezo element. So this wire must be acoustically isolated from the body of the instrument so that it does not pick up any unwanted noises. Doing this in a tight control cavity is not as simple as it is when installing a piezo transducer in an acoustic guitar. I insulate the wire with foam where it comes into the control cavity, and then wrap it around a 2” diameter by 1” thick piece of soft foam. Then the wire is routed through to the other cavity.

Then the battery box is installed and all of the connections to the preamp pc board are made.

The control cavity covers are screwed on and the instrument is ready to be strung up. Since the ¼ scale strings are a little too long for the instrument, they are installed so that the extra length is on the ball ends.

The string anchor set screws are tightened and the then the excess string is chopped off. The nut is fitted, slotted, and then glued on. Notches are filed into the bridge blade. The action is adjusted. The strap buttons are attached. The one button that is screwed to the body is attached in the normal fashion, but the three buttons that are attached to the wing are attached using 10-32 cap screws. So these three buttons are first threaded with a 10-32 tap. The wing is attached to the body using furniture connector bolts. Placement of the wing depends on the size of the player.

Once the wing is attached assembly is complete.




Up to:                 Top of this page (Part 4: Final Construction)
Back to:              Part 3: Constructing the Piezo Bridge