Archive for October, 2008
There are a couple of features that I’ve come to the conclusion are essential, when generating g-code. Sure, there are a lot of features that are necessary, but these are features that perhaps a newcomer to CNC might overlook.
When cutting out a part from a piece of wood, there is a moment when the bit will cut through the last piece of wood holding the part to the rest of the wood. At this point the forces may cause the part to simply be forced out instead of precisely cut out. If the part is complex it is possible that this may happen even earlier in the last cutting pass, causing the wood to be snapped and the part to be damaged.
The solution is holding tabs. These are small pieces of wood that are left in place to hold the part to the rest of the wood. After cutting has finished the tabs can be broken, perhaps with a Dremel, then sanded away. This creates control over the process of removing the part, and will avoid any damage.
It is possible to manually design in the tabs when creating the part in a CAD program, but then some manipulation is required in the g-code generator to obtain the correct toolpaths. A quicker and easier solution is to use a g-code generate that can automatically generate the tabs. The usefulness of this should not be overlooked.
Lead In Moves:
Plunges, where the bit is moved vertically into the wood, put a lot of strain on the CNC machine and the spindle. For example on my CNC machine I can sometimes see the Z-axis assembly move slightly up and back when it encounters the resistance of the wood.
The solution is to use lead in moves. These are moves that gradually move the bit vertically into the wood at an angle or from the side. This reduces the stress on the mechanical components, which should last longer. As an example for my current projects I use a lead in move of seven degrees.