Re: How does G02 & G03 work?

Clint Bach wrote:

> From: Clint Bach <clintbach@...>
>
> Hi,
>
> I need help understanding the G02 and G03 commands. I don't
> understand
> the I, J K thing and the rest of the things about it. The references
> I
> have on those commands devote about a paragraph and don't give me a
> complete picture of how to use them.

The information needed to compute a circular arc path are the starting
position, radius and
end position (at least the number of degrees to move through the arc).
One way to specify
this with minimal information is to say the arc starts at the current
position, ends at the position
specified by the new coordinates, and the radius is defined as being so
far from the start position.
In the XY plane, lets say you have a counterclockwise arc that goes from
(2,2) to (1,3), and
has a radius of 1. the program would look like this :
N100 G17 G01 X2 Y2
N110 G03 X1 Y3 I1
What the I word means is that the center of the arc is 1 unit from X
(IJK are the radius
offsets for XYZ, respectively). Note that algebraically, the offset for
the center is -1.
But, in this scheme, the direction to the center is known by the
starting and ending
coordinates, and so you don't need to specify the sign. So, the sign
has been co-opted
to mean how far. If the arc is less than or equal to 180 degrees, use a
positive sign
for the IJK value. If more than 180 degrees, use a negative sign.

Some controls allow an R word to give the radius directly, instead of
specifying
its offset from the beginning coordinate. If you use these, don't use
the IJK words.

In the above example, G17 selects the XY plane. G03 is for CCW arcs,
G02
for CW arcs. Any IJK word that is zero can be omitted.

Jon