offsetting of splines 2006sp5

I'm trying to make some extruded parts based on the parting line profile of
a casting. A lot of the entities created are splines and I need to offset
by .003 or so to make a continuous loop profile for extruded solids or cuts.
It seems like swx has a fair amount of trouble with spline entities as far
as geometry errors, etc that require tweaking of the sketch in order to get
an extrude to work. When offsets of the sketch are involved, the amount of
problems seems to increase exponentially, both with creating the offset and
on errors doing the extrudes with the sketch profile.

I think spline offsets are fairly new and I was wondering how this was done
before this sketch tool was available?
It seems like most processes that should take 30 seconds end up being a 2 or
3 hour nightmare fighting geometry errors, zero thickness errors, etc, etc,
etc.
I tried skipping the offset in the sketch and cutting down the extrusion
with Offset Surface, but that process did nothing but throw errors and waste
time as well.

I'm hoping there is a better way. Any ideas?

Thanks, Bill

 

Yes, splines can be quirky, but you shouldn't waste that much time on them.

There are several workarounds that you might try.

- if its really only .003" and there isn't a lot of curvature at the PL,
you might try moving the spline instead of offsetting. academically
speaking its a bad idea, but it might be "good enough".

- try the "move face" tool with the offset option instead of trying to
do a cut.

- extrude a surface and try the "replace face" command instead of a cut.

- offset the faces of the PL, extend them if necessary, and do a replace
face.

- if its more than one spline, you might check it to make sure the
endpoints of the spline are touching. you might also try to to use a fit
spline to join them together, again, a bad idea academically speaking,
but it might get you where you need to go. think about what the
tolerance is on the area which you're messing with, and if its not
critical, a little here or there may not matter that much.

 

If your spline is planer, try creating a planar surface, opening a new
sketch, and offsetting the edge of the surface. That worked long before SW
was actually able to offset splines, and, IMO, produces much more reliable
results.

 

It's hard to say because it is not clear (at least to me) from your
post how the offset splines are being introduced into your problem.

In the old days, we couldn't offset a 2D spline. We would have to
close out of the sketch and start a new sketch where we COULD offset
the spline. If it is a 2D spline, or can be converted into a 2D
spline, I would start THERE if the offset didn't work in the same
sketch (always nice to go back to the old warkarounds).

Since you are talking about extrudes, that indcates to me a problem
that can be made into a planar problem. Even if your splines are 3D,
you can try to convert them into 2D sketch and do the above, or do
something along the lines of what Brian suggested and extrude the 3D
spline along whatever vector is appropriate, offset the surface .003,
and maybe (though I hate to say it because it is not the mose robust
feature in the world) use an intersection curve to get your spline - or
convert the edge for that matter.

matt's advice was also quite good.

You can also do a thin extrude and offset both directions at once -
just don't merge the new body and delete it when you are done with it

If none of this helped, is there any chance that we can get more
detail?
Ed