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What Are Toolpaths and G-code?
When your CNC machine is running, it is executing G-code, which was created by defining toolpaths. Think of
toolpaths as your visual guide to
“
programming
”
your CNC machine. Toolpaths tell the machine how to cut your
design into the material. They tell the machine what tool to use, what area of the material to cut, and how fast to
cut. Toolpaths tell the machine how deep to cut each pass and how deep to cut when the feature is finished. The
machine has both depth per pass and max depth parameters because the end mill cuts toolpath depth a little at a
time, if the end mill tried to cut out the entire depth at once, it would either get stuck, or cause a tearout (a rip in
the material).
You never have to look at G-
code if you don’t want to. It’s not vital to know or understand how it works or how to
read it. But, it is important is to understand that G-code is made from toolpaths. You will be using Carbide Create
(for 2D milling) or MeshCAM (for 3D milling) to make these toolpaths.
Toolpath Types
In Carbide Create, you’ll encounter
four basic toolpath types:
•
Inside Cut: Offsets the cutter to the inside of the feature.
•
Outside Cut: Offsets the cutter to the outside of the feature.
•
Pocket: Clears everything inside the feature.
•
Engrave: Cuts directly on the line (no offset).
We use the term
offset
to describe the toolpaths. In this case, offsetting means to move the cutting edge of the end
mill to one side of the line or the other.
Understanding Offset and Kerf
If you were to cut a board on your miter saw to 12
″
, you would measure and mark a line 12
″
from one end of the
board. What would happen, then, if you cut the board exactly on that line, with the saw blade cutting right down
the middle of the line? Would your board measure 12
″
after the cut?
No! The board would not be cut to 12
″
because of the
kerf
. The kerf is the cutting width of the blade, which, in
most cases, would be
1
/
8
″
. If you cut exactly down the center of the line, half of your blade would be on one side of
the line and half of your blade would be on the other side of the line. Because of this, your board would measure
1
/
16
″
shorter than you anticipated.
If you wanted to cut the part to exactly 12
″
, you would need to keep your blade to the opposite side of the line you
marked. This would ensure the blade did not cut into the material that you actually wanted to keep.
When creating toolpaths, we need to do exactly the same thing to account for the kerf. Each cutter you use will
have a kerf that is equal to the cutter’s diameter. When you are creating toolpaths, it is your job to define where
that kerf will be cut from by choosing the correct toolpath type for the type of part you are milling. Then, it will be
Carbide Create’s job to generate the correct toolpath based on your input and the cutter’s diameter.
