Splines then Offset Problem???

Hi,

I am having some issues with offsetting splines... it is a long
set-up/explanation here so only the brave should read this!

Question:

If my original spline curve looked fine, why does the offset (bidirectional)
of the same great looking curve look so bad (piecewise approximated) when it
is offset? p.s. it works great (smooth) with AutoCAD 2000 Lt... go figure
:-\

Conditions:

I have a part that consists of a curved groove for cam pin - it is a plate
with a groove cut in it for a pin to "trace/track" thru.

Anyway, the spline I created is then put on a drawing, then exported to a
DXF file for the CNC machine that uses it as the centerline for cutting a
groove of constant width... and it looks great - a high number of points,
and thus a smooth looking curve that is cut with little if any linear
segments noticeable. The problem is that I need to add a few other features
to the part, and so the CNC is not just a simple "follow the line" cut, the
corners have special bumps, etc...

To over come this issue, I simply created the groove I want... i.e. I define
the walls of the groove - I need to this anyway so that I can do a motion
simulation of the assembly to ensure proper operation of the system.

And as a side note, to have SW motion simulate this type of "groove plate
cam" with a "CAM Mate", you need to make the entire cut of the cam groove
within one feature - i.e. one sketch cut, all tangent lines, spline, curves,
etc. with no addition other features adding to the desired groove like,
fillets, altered curves in the corners, etc. If you do not create the slot
in this way, the mate will fail, and so will the simulation - it took 2 days
of "VARing around" to solve this anomaly... anyway,

When, I create an offset from the original spline (to make a groove), create
a feature cut into the part, then put the part on a drawing, then export a
DXF file it has issues.

The once smooth curve is now a piecewise approximation of the curve and it
looks coarse - I would say 1/10th the number of points, maybe less.



Thanks for any help,

Aron
SW2006, sp4.1

 

I've had similar issues with spline exportation before. In those cases,
using a fit spline ( under tools-spline tools ) , then deleting the solid
body, and exporting the geometry, produced superior results. The fit spline
tool allows you to set spline tolerance rather than using SW internal
tolerancing.