G00 And G01 G-Codes: CNC Linear Motion - CNCCookbook

Specifying Linear Motion With X, Y, and Z

Note that simply specifying G00 or G01 does not cause any motion to happen–they merely tell the controller what type of motion is expected when you finally tell it where to move to. For actual motion you need to specify a destination using the X, Y, and Z words. We’ve talked about how the coordinate system works previously, so you should be quite familiar with XYZ moves. As a reminder, to move to the part zero, we might issue a command like this:

G00 X0Y0Z0

We can also do it this way:

G00 (Or use G01 if you want to go slower)

X0Y0Z0

When we specify multiple coordinates on a line, we get what’s called interpolated motion or an interpolated move. That fancy word just means more than one axis of the machine is moving at the same time. In fact, the controller will move them all at exactly the right speed relative to one another so that the cutter follows a straight line to the destination and moves at the feedrate. Imagine trying to do a coordinated 3 axis move at an exact feedrate on a manual machine. I know guys that can shift a stick shift on a car with their knee while both hands are busy (not recommended!), but I have yet to see a machinist do a coordinated 3 axis move with manual handwheels!

If we specify the same destination, but spread the coordinates over multiple lines, each line is a separate move:

G00

X0Y0 (Move to X0Y0 in one move, keeping Z constant)

Z0 (Move to Z0 in one move, keeping X and Y constant)

Remember, G00 and G01 are modal, so we only have to specify them when we want to change modes.

Careful With Z!

The concept of interpolated moves raises an interesting issue for the Z axis (or whichever axis controls your depth of cut). It’s often a good idea to move the depth-of-cut-axis on its own, rather than as coordinated motion with other axes. Doing so just makes it easier to “eyeball” whether you’re going to have a problem (collision is the technical term) as the cutter gets close to the workpiece and fixturing. It’s really hard for the human eye to judge motion in multiple axes, particularly if you have to move a long ways in X and Y and a relatively shorter distance in Z. By first moving in X and Y and then moving in Z as shown in the example above, it’s much easier to judge whether an accidental collision is about to take place. You’re also much less likely to hit some random object sticking up, like a clamp, if you keep the cutter high until you’re directly over where you want to start cutting.

The downside to this approach is it might be slightly slower than the coordinated move. If you’re trying to wring every last second out of a job, start out making 2 moves and then when you’re sure you’ve got the job running smoothly, update the program on a future run.

Entering a Cut

While you will often see programs and machinists that take the cutter straight into the material to begin a cut, this is not the best approach for cutter life and surface finish. The Feeds and Speeds course talks more about this in the section on toolpaths, but ideally you’d like to enter with some sort of an arc move that gradually builds the cutting forces instead of hammering straight in with a plunge cut of some kind. This makes it less likely you’ll chip the cutter, especially in harder materials.

To do that, we’ll need to understand arc moves, the subject of our next chapter.

Exercises

1. If you haven’t already, sign up for the G-Wizard Calculator’s free trial and start going through the free Feeds and Speeds Course to learn more about feedrates.

2. Try some “etch-a-sketch” programming. Draw out a figure by hand on graph paper so you can see the coordinates easily. Now using the G-Wizard Editor, start trying to enter the correct G00 and G01 moves to create a cut that resembles that figure. Use G00 to position close to the starting point, set the Feed and Speed up, and then start making G01 cuts

Next Article: Circular Arcs With G02 and G03