All the hard work would have now been done, if I had got the waterjets and had finished designing the stern. We will have to wait for that, as well as a delivery of balsa... But I have a couple of spare sheets
of balsa and a few final parts, so I can give you a short sample of how things will go on from here while the machine
is cutting them.
We want to cut parts out of a 4"x36" balsa sheet so I draw up the boundaries, and fit the parts in at appropriate places (fig36). The sheet is oriented vertically, because that's how my CNC machine
wants to see it, and the top right corner is positioned at 0:0, so I know where my origin is.
Then I remove all the lines that I don't need to cut. Because I have lined up the long straight edges with the edge of the balsa, I don't need to cut along them. I don't need to cut the boundary lines either - so I have a rather odd drawing for final cutting as at fig37.
From now on we don't need to look at any more drawings. I save just the bits I want to cut as a .DXF file - which is a standard CAD drawing format. Then I take this file and input it to a free software package called 'DXF2Gcode'. Which, you will not be surprised to hear, outputs instructions for cutting those lines in G Code, which is a standard language for controlling cutting tools. The language looks like this - my comments in brackets:
G90 (Absolute programming)
G21 (units in millimeters)
G17 (We are working in the XY plane)
G40 (Cancel automatic tool radius compensation.)
G49 (Cancel tool length compensation.)
G28 (go to the pre-programmed Zero position directly over the balsa sheet)
G92 x0y0z0 (Set this position to Origin Zero. All distances will now be measured from here)
G0 Z -10.000 (drop the cutting tool to height -10mm - just above the balsa)
(*** LAYER: Layer1 ***)
(* SHAPE Nr: 2 *)
G0 X +0.000 Y -68.551 (go to the first place to start cutting)
F60 (set the feed rate to 60)
G1 Z -15.400 (drop the cutting tool through the z axis to height -15.4 - this cuts almost completely through the balsa, leaving just a thin web underneath to hold the part in place)
G1 X -25.258 Y -68.525 (Move the cutting tool along the x,y axis to cut the first line)
G1 X -25.255 Y -65.350 (Move the cutting tool along the x,y axis to cut the second line line)
G1 X +0.000 Y -65.350 (Move the cutting tool along the x,y axis to cut the third line)
G1 Z -10.000 (raise the cutting tool along the z axis out of the balsa)
You can easily learn the basic commands - but you don't need to as DXF2Gcode just creates a working cutting file for you.
Next, you put some balsa in the machine
, turn it on and send the G Code commands to it. This is done with another free software package called 'G Code Sender'. The names are quite descriptive! I enclose some photos of what happens next, and a 'media file' (video) which, as you know, you download by clicking on it, and then clicking on the miniature little blue square on the top left of the screen. As you can see, there is very little dust with a thin cutting tool, and the sound from a 12v motor running at 10v is low. This was recorded with a camera
within a foot of the cutting tool...
After that, it's just an evening of taking the parts out of the balsa sheets
, assembling them and gluing up...