|
Machining Natural Shell
(Mother of Pearl, Abalone, etc)
|
|
Mother-of-pearl, abalone, and other shell products (nacre) are naturally
occurring composites of inorganic platelet/crystals (calcium carbonate)
imbedded in a witches brew of organic binders. The platelets are stacked
together in an offset pattern like microscopic bricks, an arrangement that gives natural
shell its incredible strength and resistance to the propagation of
transverse cracks. The thickness of each platelet is comparable to the
wavelength of visible light (500 nanometers) so that the stack
diffracts incoming light into the incredible rainbow patterns that make
this material so desirable for inlay.
Because the composite is laid down by the epithelial cells of the
resident mollusk, the consistency if successive layers can vary
dramatically. The marine environment in which the shell is formed also
contributes material to the composite, a fact that increases the difficulty
of machining and shaping natural shell into useable pieces. Adding to the
difficulty is the tendency of the cutting debris to pack into the kerf being
formed
as well as into the flutes of any rotary cutter.
Although much progress has been made in the form
of the laminated shell products (invented by Larry Sifel and Chuck
Erikson), it is still VERY hard, if not impossible to arrive at a chart
of reliable feeds and speeds for cutting natural shell products.
Nonetheless, the stunning beauty that can be wrought using these rather
pathological materials, inspires luthiers, pool cue makers, and
furniture makers to continue developing new techniques for shaping and
forming natural shell.
|
sample courtesy of Larry Sifel, Pearlworks |
sample courtesy of Bryan England,
Custom Inlay
|
With the application of CNC (Computer Numerical
Control) and the development of a new generation of solid carbide
cutters, shapes of great precision and elegance can be fashioned from
virtually any shell material. Bryan England of Custom Inlay (Caneyville,
Ky)
supplies inlay parts and components to many luthiers, custom knife
makers, and cabinet makers. The microphotograph at left is part of a
white pearl logo for the Gibson Guitar Co. |
 Larry
Sifel and his crew at Pearlworks (Charlotte Hall, MD) set the bar almost
impossibly high with this floral burst created for the C.F. Martin & Co.
signature guitar series.
It is exactly what it looks like. Abalone
inlaid in a spider-work of white mother-of-pearl. Although it appears too delicate to
touch, it is remarkably tough. Composed of a series of intertwined
"florets", the burst winds its way up the entire fingerboard
of the instrument before merging
with the stylized company logo on the tune head. Larry developed
the sequential inlay techniques, material fixturing and a host of other
innovations that make the production of this, and other shell
masterpieces look almost easy.
Of course, mastering these techniques is quite
another matter. As you might imagine, the first step is figuring out how
to cut shell without breaking a bit every 5 minutes. Although a
comprehensive speeds and feeds table does not yet exist, the experiences
of some accomplished inlay artists can serve as guidelines for getting
started with this amazing family of materials. |
sample courtesy of Larry Sifel, Pearlworks |
click on image for cutting parameters |
Santa Cruz Guitars, the brainchild (and
labor of love) of Richard Hoover has been the birthing place of some
of the finest acoustic guitars to be had on this planet*. In
addition to their incredible instruments, one of the distinguishing
characteristics of Santa Cruz Guitars is their willingness to
embrace new technologies to extend and enhance the capabilities of
the artists and luthiers working there.
* If you don't believe me,
check out their
player list. |
| Reith Guitars / Custom Luthier produces some of the
most innovative, dynamic and smooth playing electric
guitars on the market. Originally a software engineer, Todd has
incorporated 3D modeling and precision 3-axis CNC machining into
virtually all aspects of guitar fabrication. Featuring custom
solid aluminum Sonic-BlockT bridges, headless tuners, and
graphite headless necks, each Reith guitar is a one-of-a-kind
instrument with unbelievable clarity and seemingly bottomless
sustain.Optimized |
click on image for cutting
parameters |
Optimized Shell Cutters Feeds and Speeds
click on image to enlarge |
Diameter |
Depth / Pass |
Speed
(RPM) |
Feed
(IPM) |
Infeed / Plunge
(IPM) |
| 0.0100" (0.25mm) |
0.005" (0.125mm) |
24,000 |
4 |
2.0 |
| 0.0156" (0.40mm) |
0.010" (0.25mm) |
24,000 |
5 |
2.5 |
| 0.0200" (0.51mm) |
0.013" (0.33mm) |
24,000 |
7.5 |
3.0 |
| 0.0250" (0.64mm |
0.016" (0.41mm) |
24,000 |
9.5 |
3.0 |
| 0.0313" (0.80mm) |
0.020" (0.51mm) |
24,000 |
12 |
5.0 |
| 0.0625" (1.59mm) |
0.040" (1.00mm) |
24,000 |
28 |
5.0 |
|
