Liutaio Mottola Stringed Instrument Design

Woodworkers' Popup Units Conversion Tool / Calculator

Calculator converts to/from decimal inches, fractional inches, millimeters. Popups must be enabled for this site. From the Liutaio Mottola lutherie information website.

Did you know ....

.... you can click on most of the assembly photos on this site to enlarge them for a close look? Also, hovering the cursor over most linear dimension values will convert the values to decimal inches, fractional inches, and SI units.

Construction Details of the
Tinozza Acoustic Bass Guitar

As an acoustic bass guitar the Tinozza shares most construction details with other ABGs and the flattop guitars from which they are derived. This page does not provide complete construction instructions. It assumes that you already know how to construct a flattop guitar or can use one of the readily available books that describe this type of construction in detail. What is included here are some comments and pictures on the construction of some of the features that are unique to this instrument.

Initially appeared: June 13, 2006
Last updated: Saturday, November 25, 2017

Rib Reenforcement Strips

Flattop guitars don't often use these, but on an instrument with such deep sides they are pretty much a necessity.

The Neck

Construction of the neck is typical of flattop guitars that use a bolt-on neck, although a neck extension is used under the fingerboard and a threaded boss is glued to the underside of the end of the fingerboard.

The threaded inserts for the neck attachment bolts are set into a shallow pocket in the face of the heel. I do this to make it easier to fit and reset the neck using the sandpaper pull method. The pocket makes this process quicker as there is less wood to take away. For more on the bolt-on neck joint, see Bolt-on Neck Joint for Acoustic Instruments. This instrument features a completely removable bolt-on neck – the fingerboard extension is not glued to the top but is instead screwed to the top using a lightweight nylon screw screwed into a threaded boss on the end of the fingerboard.

The neck extension core is present only as a support for the trussrod. On this instrument the trussrod adjusting nut is at the headstock end. Unfortunately off the shelf trussrods are not available in lengths entirely suitable for ABGs and a long electric bass trussrod was used in this neck. The neck extension supports the extra length of the trussrod.

The steps involved in building the neck are roughly as follows. The neck shaft and heel are cut out as per any flattop guitar. The pocket and holes for the bolt-on neck inserts are cut in the heel face. A pocket is routed to accept the end of the neck extension and the neck extension is glued in place. The top surface of the neck is planed smooth and the slot for the trussrod is routed. The trussrod is inserted and the fingerboard is glued to the neck. The boss is shaped, drilled, threaded, and then glued to the underside of the fingerboard.

The Plates

To increase the mass a bit and lower the resonant frequencies of the instrument, both plates are on the thick side – about 0.125" each, but thinned a bit around the edges. Both are domed, the top to a 30' radius and the back to a 15' radius. Back bracing is standard ladder style:

The top is braced with two longitudinal braces and two transverse braces:

A few things will be obvious from studying the picture above. The longitudinal braces get pocketed into the neck block at the neck end but the ends float at the other end. The top transverse brace is quite heavy as it supports the end of the neck. There is a thick tab above the top transverse bar. A hole will be drilled through this for the screw that attaches the fingerboard to the top. The lower transverse bar is thin and not very high. Not a lot of bracing is needed here. Even though the strings do not terminate at the bridge, there is a bridge plate. This is 1/4" thick. It helps add mass at a critical spot and helps lover the resonant frequencies of the body. The entire area around the sound hole has a 1/8" thick patch. The one shown is made from 1/8" thick Baltic birch plywood.

The String Anchors

Since the wound portion of bass strings are too thick to be wound around the tuning posts, one can never be too cavalier about fitting the strings of any bass. In the Tinozza bass the strings are run into holes at the back of the body, through two string anchor blocks, and then exit the body through the top. The string anchor blocks are shaped and drilled before they are glued to the ribs. Here are all the blocks for the instrument:

Since the angle at which the strings approach the anchor blocks is acute, string tension tends to force the blocks together, which would tend to bend the ribs at the butt end. After the blocks are glued into the ribs a small piece of Baltic birch ply is glued across the front surfaces of the anchor blocks near the top to counteract this. Here's what the butt end looks like from the inside:

The Neck Joint

After the top is glued to the ribs a slot is routed into the top to accommodate the neck extension and the threaded boss. The slot is routed right through the neck block. It is also routed through the tab attached to the upper transverse brace, but here only deep enough to clear the boss.

From the inside it looks like this. Note the hole in the tab for the screw that attaches the neck to the top.

And here's what it looks like from the inside when the neck is bolted on.

Attaching the Bridge

The bridge is glued on. As built, the bridge cannot be glued on after the body is fully assembled. Adding an access port to the butt end of the instrument would enable the bridge to be glued on after the body was sealed up, but the instrument shown doesn't have one so the bridge is glued on after the top is attached to the ribs and before the back is put on. I do this in the go bar deck. A block that is deeper than the depth of the ribs is placed under the bridge plate so the bridge can be clamped down with go bars.

The Bridge Saddle

The length of string between the bridge saddle and the string anchor is angled at approximately 15 degrees from the line of the string from the nut to the bridge saddle. This is highly idiosyncratic, and it means that the bridge saddle must be deeply notched to keep the strings from sliding off to the sides. This also means that it is the side surface of the notch that really positions the string at the saddle. On this instrument the saddle notches are as deep as the diameters of the strings. The saddle itself is 3/16" thick as it does need to bear a good deal of side force. This should all be obvious in the closeup of the bridge and saddle.