Re: [CAD_CAM_EDM_DRO] Radius compensation - Z axis

Ethan Vos wrote:

> Good morning all. I have a problem that I just can't seem to get my head
> around.
>
> I think I understand radius compensation in the X and Y axis but not in the
> Z axis. I'm using a ball nose mill (.750) to mill a curved track in either
> the XZ, YZ, or XYZ plane. There are six of these tracks around a center so
> 2 of them use 2 axes but 4 of them use 3 axes simultaneously
>
> I thought about just programming the spherical center-point of the ball
> nose to cut a radius that is .375 smaller than what I need, but I'm not
> sure if that's the best plan.
>
> I'm worried that radius compensation would do nothing more than move the
> groove in only one axis, i.e. if I use a radius compensation on a G02 or
> G03 in the XZ plane, would the groove be moved in the X axis by the
> compensation amount or would the radius of the G02 or G03 be increased by
> the compensation amount?
>
> I guess what I really need is spherical compensation instead of radius
> compensation.

I don't think EMC or many other controls do spherical compensation.
Radius compensation is pretty standard, and well defined. It works
pretty well with all tool types, although the definition is always that
it works ate one radius only. So, if you were using a ball-nose or
radiused cutter, you'd need to specify the radius at the actual radius
of the part of the tool that is cutting into the work. Ie. if you had a ball-

nose 1/2" cutter that was cutting half way between the center and
the full diameter, ie. a 1/8" radius, then you'd need to have that
programmed into the tool table, meaning you'd tell the CNC control
it was a 1/4" dia tool, not 1/2". As the tool progresses across a
contour, the radius of the tool touching the work will likely change,
making it much more complicated. I think what you need to do
is have the CAM program, which has the full definition of the surface
available to it make these computations, not the CNC control.

Anyway, as far as I know, G41 and G42 only correct X and Y, but
not Z, no matter what plane is selected. G43 corrects Z for tool
length only, so it is just a constant addition or subtraction to the
Z coordinate, not correlated with other axes.

> I'm using a horizontal machine if it makes any difference.

No, the relationship of the axes is the same (or should be) so
the CAD, CAM and CNC software all don't know the difference.

Jon