Hello,
Most of the models I build require a 2mm wall thickness for plastic parts. I often need to rebuild broken Nurbs surfaces on the generated offset surfaces. Does anyone have effective solutions for quickly and accurately generating uniform wall thicknesses? Is there a better tool than offset surface? I am thinking of exporting my models out as solids and then shelling them out in a dedicated solid modeling software to get around this.
Thank You
Hi Justin - can you post an example or two of the input and broken output?
-Pascal
How about the command _Shell ?
Be carful with fillets and complex transitions.
sometimes you can avoid problems by keeping the surfaces without fillets.
offset the sharp polysurface and add corresponding fillets after the offsetSrf.
to get more help post files / examples.
kind regards - tom
I think you will find that your offset distance may be greater than the minimum radius of curvature.
This is a design fail and not easily resolved. (no push button solution)
The best method is design with the understanding that you will need to offset for the wall thickness. If you choose to use radii smaller than the offset distance for whatever reason, then your only recourse is a manual (time consuming) re-evaluation and reconstruction of surfaces where offset fails. This problem will exist in any dedicated solid modeling software.
Here is a less complex model.
Offset Example.3dm (14.8 MB)
I tried using both offsetsrf and shell, but still came out with naked edges on the interior surface.
That make sense, I’ll try that next time!
Makes sense. I have resorted to repairing the interior surfaces with G0 to deal with non-existent radii after shell procedure.
do you models need to have perfect numerical offsets or can they be what I refer to as a “wax” offset that is more like what you would get in the old days with sheetwax being applied to a mold to generate the surfaces for a cavity which would be then panographed into a block of billet.
if a wax offset would work, then shrinkwrap is your new best friend, grab the v8 wip and give it a try.
2mm offset on this ? to the inner or outer ?
To the inner.
I try to design to near perfect numerical offset so the plastic cool uniformly inside the mold. How much thickness variance is possible I’m not entirely sure.
I saw the shrinkwrap tool, looks cool!
and what do you expect to happen between those 2 surfaces - there distance is less then 4mm
(or did you upload the wrong file, layer is called scaled)
EDIT
OH Sorry—
units are inch in your file ;-(
… ok not sure how big / precise / units your object is.
converting to millimeters with scalling…
_what
will show an edge Tolerance
Edge Tolerances: 0.0000 to 0.0424
so i think your document Tolerance should be rougher. maybe 0.1 ?
offset will then fail at this specific detail.
testing with
_edgeContinuity
shows some nearly tangential corner, where 4 surfaces meet.
my guess: the rough edge Tolerance together with this nearly tangential corner is to much for _offsetSrf to handle within tolerances.
offsetting the single surfaces (explode the polysurface) will show the geometrical problems of the edge-Tolerance and nearly tangential corner:
(offset in red)
with all this in mind - using a tolerance from 0.1 and the option Corner=round i get a solid solution with
_offsetSrf
Offset Example_02_tp.3dm (1.6 MB)
Ok, so if I need to model and offset in .01 tolerance all surfaces edges need to be at least tangential, or curve continuous, for the offset procedure to not break the interior surface?
see edit / update of my post above
i would claim that the edge-tolerance of your model should be one digit more precise to not run into problems.
you can query this with the command
_what
And somehow those 4-surface corners are causing problems if the surfaces eges are not tangential or close to document angle tolernace.
analyse with
_edgeContinuity
Ok, I can see how that could create naked edges in the offset. The input Nurbs have to be totally dialed in (within document tolerances) for the offset tool to function effectively. Thank You!
