The luthier's corner has been good to me. I've learned most everything I know about bass building from y'all, so I feel it's time for me to give back. Here is a tutorial on Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM), with the end goal of CNC machining a bass guitar in mind.
I learned how to make my first bass in 2008 by hanging out in this forum, but I've been designing things in Rhinoceros for fun since 1999; at this point I can get it to do what I need. In 2012 I built a CNC router as a bridge between my CAD hobby and my bass building hobby, and I had to overcome a steep learning curve to put it all together. But at this point I've built 3 complete instruments with CNC assistance, plus a few unassembled bodies and necks.
I was originally going to make a build thread featuring my CNC machine in action, but there are already some great CNC build threads here. So instead I thought I'd demystify the process, show what goes into it before you ever turn on the router.
In this tutorial we will design a bass in a modeling program, then turn the design into gcode files that the CNC machine uses to cut out the parts.
The software that I will be using is
Rhinoceros for the 2D and 3D design,
CamBam for 2.5D gcode, and
MeshCam for 3D gcode. There are hundreds of other programs out there with perhaps better features, but I can get it done with this relatively inexpensive suite.
Below is an outline of steps, and links to videos where I'll work my way through this method. If I do something you have questions about, feel free to ask.I don't intend it to be a full introduction to Rhinoceros; there are hundreds of videos already for that.
Over the next few days I'll update this post with video links, and expand the outline below.
Video 1: Setting up Rhino file, establishing critical dimensions Video 2: Drawing a body from an image and from scratch, drawing headstock Video 3: Pocket and cavity design, 3D neck back design and analysis
1. CAD (Rhinoceros)
A: RHINO SETUP: VIDEO
1. Open a new file, go to "file>save", and save it.
2. Open "file>settings>units", adjust page units to your preference, metric or imperial. Set tolerances.
3. Open "file>settings>grid", set grid size, major and minor grid lines
4. Open "Rhinoceros>preferences>modeling aids" for nudge settings (key,distance and window), snap settings
B. CRITICAL DIMENSIONS
00. design considerations (entering arguments)
a. Scale length
b. Number of strings
c. Bridge spacing
d. nut width
e. general body size
f. hardware/pickup choices
01. Centerline scale length (34" scale centerline)
02. Nut width (1.5" nut)
03. Bridge width, Bridge spacing (2.25 bridge /4)
04. Bridge placement. envelope of saddle adjustment considered.
05. 1/4" outside of outer strings, neck lines
06. Scale lines
07. EQUAL SPACED NUT:
a. Determine string gauges you'll use, then add them. DR Lo Riders medium: G.045 D.065 A.085 E.105 = .300
b. Subtract total string width and desired edge width from nut width: 1.500-.125-.125-.300=.95
c. Divide this number by the number of between-string spaces (3 for a 4 string bass) to get the spacing: .95/3=.3166
08. Strings w thicknesses
09. guide lines for general body size, strap hang point. Clearance for fingers.(horn at 12" fret bottom horn 16th fret 3" below neck, 2" above 9" wide hips
10. Pickup type, placement.
11. Knobs
12. tuner post diameter, tangent to string
C. DESIGN
01. Sketch body, pull control points until shape is practical and pleasing.
02. Same for headstock headstock.consider tuner pegs.
03. Electronics cavity. design after you're happy with body shape
04. Knob placement.
D. SIDE PROFILE: While not used much to generate gcode files, the side profile will help you determine thicknesses of the body, neck and fretboard, depths for cavities, neck angle, headstock angle, etc. It will also help you to decide what thickness stock you will need to achieve your desired result.
01. Body thickness
02. Neck thickness
03. Neck angle
04. FB thickness
05. Headstock angle
06. Pickup cav depth
07. Electronic cav depth
E. 3D lofting
01. Body only needs lofting for 3D contours.
02. Headstock faces, if milling from a solid neck blank. If chop/flipping headstock, you can skip this.
03. Neck back contour
04. Volute
05. Heel
06. Flip things that cut from the back
07. Truss rod channel (if curved)
08. Establish index pins
2. CAM
A. 2.5D (CamBam): 2.5D refers to machining to shapes down to a specific depth. Think of making a heel pocket or pickup cavity with a router; that is 2.5D.
00. Export files from Rhino. DXF files for 2D.
01. Index
02. Heel pocket
03. pickup pockets
04. Bridge holes
05. Elec cav
06. Contours: Stepover considerations
B. 3D (MeshCam): only for neck backs and carved tops.
00. Export files from Rhino. STL files for 3D objects.
