Hey guys, here is a quick tutorial on how I surface an acoustic neck. There are certainly other ways to do it, but this is the basic process that I use.
In order to do this, you need to understand some of the basic drawing functions in Rhino such as how to create and edit lines and splines. You should also have a working understanding of how to construct geometry by using commands such as offset and mirror, as well as have a good understanding of the object snaps.
The basic procedure is to create a wireframe using splines and lines. Then this wireframe is used as a guide for the actual surfacing commands. You need to set your wireframe up correctly such that everything is tangent and coincident where appropriate. If you don't the surfacing commands won't work!
A good tip is to always keep the splines as simple as possible; don't go overboard and put more nodes on the spline than you need!
Without further ado..
1) this first step consists of laying out the fingerboard in 2D. I also drew a line from the center of the 14th fret, parallel to the Z-axis 3.5" to set the depth of the heel.
2) Next, I begin drawing the center guidlines. I drew lines along Z at the first fret and a bit in front of where the heel transition would be. These lines indicate the thickness of the carve at these positions. Next, I draw a line from the endpoint of this first line to the endpoint of the one closer to the heel.
Next I draw a spline from the end of the heel as shown, and connect it to the end of the center line drawn previously. At this point the heel center line is not tangent to the neck center line. This is OK, we will fix it later.
To make those lines tangent, I turn on heel spline's edit points by clicking the button below and selecting the spline.
Next, I move the highlighted nodes around so that it looks about like I want it to. Note that it is still not tangent, but it is closer.
Now I use the match curve command to force that heel spline to be tangent to the neck center line.
The first step in doing the headstock is to create a spline like the one shown with the edit points on (yep, that's a straight spline..but still a spline!).
In the next couple of steps, I move the edit points for this spline along the Z and X axes in order to make it round as shown.
Next, I draw the neck profiles at that first fret position, and at the beginning of the heel transition. These are probably the most important curves on this model!
Next, I sketch in a profile for the end of the heel using splines and playing around with the edit points as before.
These next two screenshots show the heel profile and some of the refined neck carve profiles.
We are now ready to surface the neck. I like the Network Surface command..it gives very consistent results. You basically click the Network Surface command and then pick the two edges of the fretboard, the center line for that section, and then the two profiles for that surface.
I surfaced this neck in 3 parts; the heel transition surface, the neck shank, and the headstock fade-out surface.
Please note that some editing was done (using split, and match curve) in order to partition the wireframe in the 3 sections that I want.
Carve surface is now finished..
And just because it is easy to do (took less than 2 minutes to do this CAM portion)...here's a screenshot showing a toolpath that I could use to cut this. Using a .050" stepover between toolpaths and running at 40 inches (this is slow in the world of CNC), we can carve this neck in about 27 minutes. It would be prudent to do a perimeter cut as well..but that would not be time consuming.
I hope you enjoyed checking this out, let me know if you have any questions. Rhino is good stuff!
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