User's Guide

Design vs Project

It is important to understand Designs and Projects, and how they differ from each other.

Design

A Design describes a model of an instrument, such as Dreadnought, OM, or L-00. A Design includes:

• Shape of the instrument
• Arches (if any)
• Bracing patterns
• Fretboard

One Design can be used in multiple Projects.

When you add a custom Design, it will be based on one of:

• A built-in stock design (such as Dreadnought, OM, etc.)
• A custom design that you have previously created

See also:

• Design Library
• Stock Design vs Custom Design

Project

A Project is a specific instrument that you are making. If you are building two identical instruments, one for Sally and one for Alan, there will be a separate Project for each. A Project includes:

• A design
• Chladni pattern photos
• Spectrum analyzer samples
• Notes

See also:

• Project Library
• Active Project

Demo Project and Demo Design

Luthier Lab includes a starter project called Demo Project, which uses a design called Demo Design. Demo Project (and Demo Design) can be used to experiment with the Luthier Lab tools. You can think of it as a “sandbox” or “scratch” area.

When you are ready to create your own project, see Adding a Project.

Active Project

The active project is the currently selected project. Any changes you make will be stored in that project. The first time you run Luthier Lab, the active project will be the project named Demo Project.

The active project is shown at the top of the Navigation Drawer.

See also:

• Adding a project
• Changing the Active Project

Changing the Active Project

You can change the active project by pressing the edit icon () next to the project name (at the top of the Navigation Drawer).

The Choose project dialog will be displayed, with a list of your projects. You can select one of those projects, or press the plus sign icon () to create a new project.

In this example there are three projects. You can see that Alan's Project and Sally's Project share a design (My Design). The Demo Project uses design Demo Design, which is not shared with any other projects.

Component Controls

The components are adjusted using a shape component control. Pressing on a component will show the control for adjusting that component. The control will appear at the bottom of the screen. In the example above, the control for the lower circle is shown.

The control has a tab for each attribute that can be adjusted (in this example: width, diameter, and offset). Each tab has a slider for adjusting the value of the attribute (in this example: width). You can see the change in the shape as you adjust the value. If you prefer, you can enter an exact value by pressing on the "value button" next to the slider.

Dismiss the component control by pressing the back button or pressing anywhere on the shape.

Length and neck flat

Pressing on the instrument outside of any of the circles will display the control for adjusting the length and the neck flat.

Length	Length of body
Neck Flat	Flat area at neck join (optional)

Sound hole

Pressing on the sound hole circle will show its control:

Diameter	Sound hole's diameter
Offset	Distance from neck join to center of sound hole

Circles

Pressing on each of the circles (lower bout, waist, upper bout) will show the circle control:

Control	Lower Bout	Waist	Upper Bout
Width	Width of instrument at lower bout	Width of instrument at waist	Width of instrument at upper bout
Diameter	Lower bout circle's diameter	Waist circle's diameter	Upper bout circle's diameter
Offset	Distance from bottom of lower bout circle to tail of body	Distance from bottom of waist circle to tail of body	Distance from top of upper bout circle to neck join

Split Circles

While many guitar shapes can be described using three circles and the lines connecting them, there are several popular designs (such as OM), where more control is needed.

The Split circles option (in the menu ) splits each circle into two half circles. You can independently control the diameter of the top and bottom halves of the circles.

Pressing on each of the circles (lower bout, waist, upper bout) will show the split-circle control:

Control	Lower Bout	Waist	Upper Bout
Width	Width of instrument at lower bout	Width of instrument at waist	Width of instrument at upper bout
Top	Lower bout circle's top diameter	Waist circle's top diameter	Upper bout circle's top diameter
Bottom	Lower bout circle's bottom diameter	Waist circle's bottom diameter	Upper bout circle's bottom diameter
Offset	Distance from bottom of lower bout circle to tail of body	Distance from bottom of waist circle to tail of body	Distance from top of upper bout circle to neck join

Cutaways

An instrument can have a single cutaway (on the treble side), or double cutaways (on treble and bass sides).  The bass cutaway can mirror the treble cutaway, or be independent of the treble cutaway.

The Cutaway option (in the menu ) enables the treble cutaway. When the treble cutaway is enabled, you can add a bass cutaway. To get a mirror image bass cutaway, select the Symmetrical cutaway option. To get an independent bass cutaway, select the Bass cutaway option.

Each cutaway is defined by two circles:

• Cut circle - depth and width of material to be removed
• Edge Circle - offset and width of remaining material

Pressing on either the Cut circle or the Edge circle will show its control. (In this example, the Split circle option is turned on, so the controls allow you to specify the diameter of the left and right halves of the circles.)

Control	Cut	Edge
Depth	Depth of the cutaway from the neck join	N/A
Left	Left cut cutaway diameter	Left edge cutaway diameter
Right	Right cut cutaway diameter	Right edge cutaway diameter
Offset	Distance from the centerline to the side of the cut	Distance from the neck join to body perimeter.

Scale Shape

Sometimes an existing shape is close to the desired shape, but the size is wrong. For example, you might want to make a ukulele based on an OM.

You can scale the shape by selecting the Scale shape option from the menu (). Enter the desired length for the shape, and all other values for the shape will be scaled proportionally.

Arch Height

The arch height is displayed in the action bar at the top of the screen. In this example, the top’s arch height is set to 0.75”.

Pressing the value (0.75 IN) displays a dialog for changing the height. In this example, the arch height will be changed to 0.8”.

Contour Lines

Press the contour icon () (or select the Contour option in the menu) to show/hide a topological map of the arch.

Contour Interval

Select Contour interval in the menu () to adjust the vertical distance between contour lines. A smaller interval will display more contour lines.

Share/Export CAD Model

Select Share/Export CAD model in the menu () to export the top or back arches, so you can import them into a CAD tool. The file format is STL, which is accepted by most CAD tools.

Your device will give you the option to share the file to Google Drive or your email tool. Either option works, but some email servers limit the size of attachments.

Resolution

The arches are rendered as a sequence of triangles. The resolution of the model can be Coarse, Medium, or Fine.  Coarse is roughly 600 triangles. Medium is roughly 5,000 triangles. Fine is roughly 18,000 triangles (file size ~3 Megabytes).

The finer the model, the less sanding will be needed on the top/back when it comes off of the CNC machine.  Some CAD packages limit the number of triangles in an STL file to less than 10,000.

CAD Tools

Luthier Lab's STL output has been tested on the following CAD tools, as well as several other STL reader programs. If you have difficulty importing Luthier Lab's STL data into your CAD program, please contact us.

• BobCAD V24
• Fusion 360
• Onshape

Edit Controls

There are five controls for editing bracing patterns. Two of them are for manipulating existing braces and three are for drawing new braces.

Drawing Braces

Straight Brace

Use the straight brace button () to draw a straight brace. Press anywhere on the shape to start a straight brace and drag to the end position of the brace. If the start or end of the brace is near the edge of the shape, the start or end will snap to the shape.

Symmetrical Brace

The symmetrical brace is actually two braces that are symmetrical along the centerline of the shape. This is useful for drawing X braces, A braces, and fan braces.

Use the symmetrical brace button () to draw a symmetrical brace. Press anywhere on the shape to start a symmetrical brace and drag to the end position of the brace. The complementary brace is automatically drawn.

Curved Brace

Some designs use curved braces. Curved braces are drawn using cubic splines. The cubic spline is defined by two end points and two control points.

Press the curved brace button () to draw a curved brace. Press anywhere on the shape to start the curved brace and drag to the end position of the brace. A straight line is drawn between the start and end points of the brace.

The curved brace is automatically selected after it is drawn. Press inside the endpoint circles to move the end points. The two control circles are also shown. Press inside the control point circles to adjust the curved line. The line does not necessarily pass through the control points.

A smooth curve is drawn based on the position of the end points and the control points. It takes practice manipulating the control points to get the shape of the curved brace to the desired position

Menu Options

Delete Brace

When a brace is selected, the delete icon () is displayed on the action bar. Press the delete icon to delete the selected brace.

Delete All

Deletes all of the braces.

Choose Stock Pattern

Allows you to use a stock bracing pattern as a starting point for your custom bracing pattern. The selected brace pattern is added to the existing design. It does not replace any existing braces.

See: Stock Bracing Patterns

Grid

Displays a grid on the screen. The grid squares are ½ inch when using Imperial units, and 1 cm when using metric units. See also: Settings: Show grid.

Snap to Brace

Enables a feature where the endpoints of braces snap to a nearby brace. This works when the editor is in manipulation mode. See also: Settings: Snap to brace.

Stock Bracing Patterns

It is often more convenient to load a stock bracing pattern into a design and then edit it to fit the shape, or otherwise alter the pattern.

There are over 30 stock bracing patterns provided. Many of these patterns were drawn on the classical shape but some are for steel string guitars and are drawn on the Small Jumbo shape.

Loading a stock pattern adds the braces of that pattern to any braces that already exist for that design. You can add two patterns from the stock bracing patterns and they will overlay each other. When this happens, it is usually easiest to delete all of the braces and start over.

Any custom bracing pattern that you create is also added to the stock bracing patterns under the name of the design.

Fretboard Values

Press the edit icon () in the action bar to raise the Fretboard values dialog. This dialog lets you set any of the attributes of the fretboard. Press in the data field for any of the values to enter a new value for that field.

• Treble scale is the scale for the treble string. It is also the scale for the whole fretboard when the fretboard is single scale. Any value from 9.0" to 39.0" is allowed.
• Bass scale is the scale for the bass string. It is ignored when the fretboard is single scale. Any value from 9.0" to 39.0" is allowed.
• Number is the number of frets on the fretboard. Any value from 1 to 40 is allowed.
• Fret at body is the fret that is at the body of the instrument. Typically 12 or 14 but any value from 1 to 40 is allowed.
• Center fret is the fret that has the same offset for the bass and treble frets on dual scale instruments.
• Width at nut is the width of the fretboard at the nut.
• Width at body is the width of the fretboard at the body join.

Values Tab(s)

There can be one or two values tabs. If the fretboard is single scale there is one tab, named VALUES. If the fretboard is dual scale, there are two tabs: TREBLE VALUES and BASS VALUES.

In this example, the fretboard is not dual scale, so there is one tab.

Each values tab has four columns:

• Num: fret number, starting at the fret closest to the nut
• Offset: distance from the nut to the center of the fret
• Delta: distance from the center of the previous fret to the center of the fret
• Done: a checkbox that you can use to keep track of your progress through any of the fretting processes (such as slotting, leveling, dressing, etc).

Create Album for Untuned Top

When taking photos of Chladni patterns for a top or back, make sure that they are placed in an album for that top or back. To create an album, select Add album from the options menu. An Add album dialog will appear. Enter the name of the album. For example, Untuned Top. This will create the album.

Create Album for Tuned Top

Use the Add album menu option to make an album for the tuned top. For this example, the new album is named Tuned top.

The pattern we saw at 338.30Hz was open at the corners. Shave the braces and find the new frequency that displays this pattern or one similar. The objective is to lower the frequency to between 245Hz and 260Hz and to close up the lower pattern so that it makes a ring. After several iterations of shaving and creating new patterns a new shape appears with the lower pattern making a ring and the frequency lowered.

At this point, work your way through the frequencies finding as many patterns as you can. Take a picture of each one. It will be saved in the new album.

Notice that the pattern that used to be at 338.30Hz is now at 249.83Hz and the lower portion of the pattern is now a closed ring. This is considered to be a tuned top.

Rename Album

Use the drop down menu to select the album that you want to rename. Select the Rename album item from the option menu. A dialog will appear to enter the new name for the current album.

Delete Album

Use the drop down menu to select the album that you want to delete. Select the Delete album item from the option menu. A dialog will appear to confirm that you want to delete the album.

Change Tone Generator Frequency

It is sometimes convenient to change the frequency of the Tone Generator from the Chladni Pattern tool. The name of a new image is the current frequency but it will replace any existing image with the same name. If you want to take two images of the same Chladni pattern, you can change the current frequency by a small amount to make a unique name.

Press the current frequency in the action bar (in this example: 440.00 HZ). A dialog will appear to set the new frequency.

Audio Sample Tab

The audio sample tab displays the current sample. Samples are one second long. You can control the display with the control sliders and the boundary markers.

• Gain: Controls the amplitude of the signal. It can range from 0 to 10 times the sampled values.
• Trigger: Stop recording based on the amplitude of the input signal, see Trigger.
• Boundary Markers: Select a portion of the sample, see Boundary Markers.
• Zoom: Zoom the audio sample display to the selected portion, see Zoom.

Boundary Markers

Selecting a Marker

Press your finger near the lower or upper boundary marker. Drag the marker to a position at the beginning or end of a section of the sample that interests you.  The selected marker will turn yellow while you drag it. The example shows that the first of several tones is selected. The remainder of the sample is grayed out.

The FFT tab will display the frequency spectrum for the selected portion of the audio sample. In this example, the dominant frequency for the selected tone is 1394.5 Hz.

You can examine the third tone in the display by moving the boundary markers to select only the third tone.

Now the FFT tab will display the frequency spectrum for the third tone. In this example, the dominant frequency for the third tone is 1068.0 Hz.

Zoom

The zoom toggle will "zoom" the audio sample display in to the elected by the boundary markers. Consider the multitone example. The third tone is selected.

This is the same audio sample with zoom enabled. It displays only the section that is selected (between the two boundary markers). The boundary markers are now at the far left and far right of the display. You can move the boundary markers into the display to further refine the selection. To select a portion of the sample greater than the current selection, you must disable zoom.

Collect Audio Sample

Press the microphone on button () to start recording audio. Press the microphone off button () to stop recording audio. The sample will be the last second of audio prior to turning off the microphone.

The most recent sample is displayed but previous samples are saved and can be viewed (see: Sample list).

Trigger

It can be very awkward to press the microphone on/off buttons while recording audio, especially when you have to pluck a string or tap on the instrument. The trigger function allows you to automatically stop recording, based on the amplitude of the input signal.

Press the Enable trigger checkbox to enable or disable triggering. The trigger value is a fraction of the maximum value the microphone picks up. A value of 0.01 will trigger on almost any sound level, and a value of 0.99 will trigger on only the loudest sounds.

When the trigger is disabled, recording will continue until you explicitly stop it. The audio sample will be the final second of the recording.

When the trigger is enabled, recording will stop when the input signal exceeds the trigger value. The audio sample will be the second after the input signal exceeds the trigger value.

Suppose you are doing an impulse excitation test on an instrument. Set the trigger to a value that is above the ambient noise in the room and press the microphone on button (). Place the microphone in front of the instrument and tap on the bridge. The tap sound should exceed the trigger threshold, and recording will continue for one second and then stop. The sample will be displayed on the audio sample page. The audio sample displayed in the image above is an example of such an impulse.

If recording stops too soon, raise the trigger value. If it doesn’t stop when the tap is done, lower the value.

Sample List

All samples taken for a given project are preserved and can be viewed. You select which sample to view by pressing the sample list icon () in the action bar. This raises the sample list dialog, a scrolling list of all of the samples. The current sample is highlighted. Select another sample to make it the current one. To dismiss the dialog: press outside of the sample list or use the back button.

The default name of each sample is the date and time that it was captured. You can change the name of a sample by pressing the rename icon (). In the image above, the current sample has been renamed to “Impulse test”.

Press the delete icon () to delete a sample.

Impulse Excitation Technique (Bonk Test)

You can capture a “signature” of an instrument by performing the Bonk Test:

1. Hang the instrument from the head stock, and dampen the strings.
2. Start the Spectrum Analyzer recording, with a Trigger value above the ambient noise level in the room.
3. Tap the saddle of the instrument with a small plastic head hammer or a hard plastic ball suspended on a string, such that when it is released from a constant distance from the instrument it strikes the saddle. (Bonk!)

   The saddle of an instrument is hard enough that it won’t be damaged by the hammer or ball. Don’t strike the body of the instrument! The ball-on-a-string method gives a more consistent impulse.

The Spectrum Analyzer will store the sound generated by the bonk and the FFT tab will show the frequency spectrum.

Tapping the instrument in this way causes it to vibrate at all frequencies at once. The signal will be stronger at the resonant frequencies and weaker at frequencies that are not resonant. You can build up a library of bonk test results and notice that certain frequency spectrums will have characteristics that correspond with similar tonal qualities.

You can then shave some braces and do the experiment again to adjust the tone of the instrument. Which braces to shave to get a particular result depends entirely on the result you are trying to get and the experience you have with shaving braces.

Name Collision

If you already have a Design/Project with the same name as the to-be-imported Design/Project, a dialog will appear giving you the option of canceling the import, or choosing a different name for the to-be-imported Design/Project.

If you are importing a Project, and there is a name collision for both the Project and the Design, the Design name conflict dialog will appear first, and then the Project name conflict dialog will appear. This gives you the opportunity to decide how you want to resolve each collision.

In this example, you are importing a project (Mike's Project), which contains the design Mike's Design, but you already have a project named Mike's Project and a design named Mike's Design. You can choose a different name for the Design and Project, or cancel each import.

Re-import Collision

If you are importing a Design/Project that you had previously imported, the Re-importing collision dialog will appear to allow you to specify how to handle the collision.

Note: The Design/Project that you are re-importing may not be indentical to the previously imported copy, as you may have modified your copy, or the other Luthier Lab user may have modified their copy.

If you are re-importing a Project, the Re-importing Design dialog will appear first, and then the Re-importing Project dialog will appear. This gives you the opportunity to decide how you want to resolve each collision.

In this example, you are re-importing a project (Mike's Project), which contains the design Mike's Design. You can:

• Choose a different name for the Design and Project
• Overwrite your existing Design and Project
• Cancel each import