Position the cutter head at the intersection of the X and Y zero lines as planned in the SET UP stage. On the controller select this point for the CNC to use as the physical X, Y zero point.
Then lower the router bit to the surface of the MOP. Select this point to be the Z zero point. The Z zero must be set up again after every bit change.
Sweep the spoilboard with a large diameter bit to ensure that the surface is true and parallel to the bit path.
CNC controller_ select USB input (lower right)
Removing the MOP: To remove the pearl from the veneer after it has been cut, immerse the veneer and the MOP in a tray of acetone for about a half hour. This will soften the glue and allow one to seperate the MOP from the veneer with a X-Acto blade or thin spatula.
The Peghead design and set up are determined entirely by the builder's taste and experience. The shape of the peghead is a variable and the guitar maker's choice. As you can see, familiar guitar brands vary significantly in the peghead shape. There are pros and cons associated with each.
Shown below are photos of three operations on the Woody peghead_
Layout of the tuning machines
Design of the peghead inlay
Cutting the pockets and the Mother of Pearl
These three operations are inter-dependent. Woody's inlay design is 11 pieces of mother of pearl, individually cut and inlaid into an ebony head plate. The converging lines of purfling (WBW) frame the pearl inlay design.
Cutting MOP: To cut the pearl, Super Glue (CA glue) the MOP blanks to a veneer of wood. Be sure that neither the veneer nor the pearl will move during the cutting operation.
To cut the pockets Woody uses a 0.045" bit to hog out the majority of the pocket. Then change the bit tp 0.025" to clean out the tight corners. Use pocket toolpaths for both. Select the correct feed and speed for your bit as explained above. (see PROGRAM)
Feed and Speed: Woody's router is not variable speed so the spindle feed (router speed) is fixed at 22,000 rpm. This spindle speed is quite high but it's all that I have. I adjust my feed rate according to the bit and materials being cut. For mother of pearl and a 0.025" bit I use a feed rate of 3mm per second.
This combination results in a very low chip load which I feel is needed for mother of pearl. To increase the chip load one would decrease the spindle speed or increase the feed rate.
For a complete explanation of speed and feed, find a tutorial explaining Chip Load and the relationship between bit diameter, the number of flutes, spindle speed, feed rate and material density. Try this:
MOP Pockets: Make sure that the headplate is positioned correctly and secured so that there is no chance that the stock will move during the cutting operation.
PROGRAM ... the toolpaths
Later, the design was modified slightly to use the D and G strings as a frame for the inlay. NOte that the bottom of the inlay design was also modified as shown below.
Change the zero Z to an elevation that is, say, a half inch above the work and execute a test run to ensure that the controller is using the correct X, Y zero points and toolpaths that are within the boundaries of the work.
EXPORT ... to the CNC controller
Direct your questions to
I hope to see you back here next month,
Toolpaths stored on the flash drive. (see EXPORT above)
The name of the toolpath should include an indicator of the type of bit. For example, a pocket toolpath that uses a 0.025" End Mill might be named Pkt25 EM. This tells me that this is a Pocket toolpath, using a 0.025" End Mill bit.
When one is confident that the execution will produce the design toolpaths, change zero Z back to the surface of the work and run the first toolpath.
After creating the toolpaths, they must be exported to the CNC controller via flash drive.
Thanks for your long attention span this month. Even when done correctly the CNC operation is tedious. It may take a while to learn. Start simple and build your know-how. I am still a beginner, but it's coming around.
In the job SET UP the software asks for the length, width and thickness of the work area, as well as the X and Y zero point. Then the progammer (you) must draw the vector design in the software. These are the lines that the machine will be programmed to follow.
We will use last month's Prep Steps to explain the design, layout and cutting of the inlay pockets and cutting of the pearl.
Head Stock/ MOP
Peghead Design, Layout and Cut
Before cutting the MOP pockets, position the headplate veneer on the spoilboard so that the center line is parallel to the path of the cutter.