Tormach PCNC 770 - Center Format Arc

Chapter 7
102
UM10350_PCNC770_Manual_0916A
Programming
It is an error if:
• Both of the axis words for the axes of the selected plane are omied
• No R word is given
• End point of the arc is the same as the current point
• G10, G28, G30 or G92 appear in the same block
It is not good pracce to program radius format arcs that are nearly full circles or are semicircles
(or nearly semicircles) because a small change in the locaon of the end point produces a much
larger change in the locaon of the center of the circle (and, hence, the middle of the arc). The
magnicaon eect is large enough that rounding error in a number can produce out-of-tolerance
cuts. Nearly full circles are outrageously bad, semicircles (and nearly so) are only very bad. Other
size arcs (in the range ny to 165 degrees or 195 to 345 degrees) are OK.
Here is an example of a radius format command to mill an arc:
G17 G02 X 1.0 Y 1.5 R 2.0 Z 0.5
That means to make a clockwise (as viewed from the posive Z-axis) circular or helical arc whose
axis is parallel to the Z-axis, ending where X=1.0, Y=1.5 and Z=0.5, with a radius of 2.0. If the starng
value of Z is 0.5, this is an arc of a circle parallel to the XY-plane; otherwise it is a helical arc.
7.5.3.2 Center Format Arc
For an arc in center format, program: G02 X~ Y~ Z~ I~ J~ (for a clockwise arc) or G03 X~
Y~ Z~ I~ J~ (for a counterclockwise arc).
Word Denition
X~ X-axis coordinate
Y~ Y-axis coordinate
Z~ Z-axis coordinate
A~ A-axis coordinate
I~ Center of arc (X coordinate)
J~ Center of arc (Y coordinate)
K~ Center of arc (Z coordinate)
In the center format, the coordinates of the end point of the arc in the selected plane are specied
along with the osets of the center of the arc from the current locaon. In this format, it is OK if the
end point of the arc is the same as the current point.
The center is specied using the two I , J, K words associated with the acve plane. These specify
the center relave to the current point at the start of the arc, dened in incremental coordinates
from the start point.