1.8 Arcs & Helices
A circular or helical arc is specified using either G2 (clockwise arc) or G3 (counterclockwise arc) at the current feed rate.
The direction (CW, CCW) is as viewed from the positive end of the axis about which the circular motion occurs.
The plane used for the circle or helix must be one between XY, YZ, or XZ.
The plane is selected with G17 (XY-plane), G18 (XZ-plane), or G19 (YZ-plane).
The P word can be used to specify the number of full turns plus the programmed arc.
The P word must be an integer. If P is unspecified, the behaviour is as if P1 was given: that is, only one full or partial turn will result.
For each P increment above 1 an extra full circle is added to the programmed arc.
Multi turn helical arcs are supported and give motion useful for milling holes or threads.
Note If a line of code makes an arc and includes rotary axis motion, the rotary axes turn so that the rotary motion starts and finishes when the XYZ motion starts and finishes.
1.8.1 Syntax
1.8.2 Center Format Arcs
Center format arcs are more accurate than radius format arcs and are the preferred format to use.
The end point of the arc along with the offset to the center of the arc from the current location are used to program arcs that are less than a full circle.
If the end point of the arc is the same as the current location a full circe is generated.
G2 or G3 axes offsets P
G2 or G3 offsets P can be used for full circles
Incremental Arc Distance Mode
This is the default Distance Mode for the arc center offsets (I, J, K) that are relative distances from the start location of the arc.
One or more axis words and one or more offsets must be programmed for an arc that is less than 360 degrees.
This mode is enabled with G91.1.
Absolute Arc Distance Mode
Arc center offsets (I, J, K) are relative distances from the current origin of the axes.
One or more axis words and both offsets must be programmed for arcs less than 360 degrees.
This mode is enabled with G90.1.
1.8.3 Radius Format Arcs
G2 or G3 axes R- P
1.8.4 Examples
1.8.5 Center format arcs incremental mode
1.8.6 Full circles and helices
( © 2018 by RosettaCNC Motion ) ( file name: full_circles_and_helices.ngc ) G21 G40 G49 G90 G54 G50 G69 M3 F2000 G0 X0 Y0 Z0 G17 ; XY plane G2 I0 J25 G18 ; XZ plane G2 I0 K25 G19 ; YZ plane G2 J0 K25 T3 M6 G52 X100 G0 X0 Y0 Z0 ; helixes G17 G2 I0 J25 Z100 P2 G0 X0 Y0 Z0 G18 ; XZ plane G2 I0 K25 Y100 P2 G0 X0 Y0 Z0 G19 ; YZ plane G2 J0 K25 X100 P2 M2