Question for Surfacing Guys
Question for Surfacing Guys
(OP)
As an assembly equipment machine design guy, I deal mostly with prismatic parts. Anything you can't easily model with extrude cuts and revolves usually makes for difficult to fabricate parts, so we try to keep it simple. However, I'm now in a situation where I need to model something to closely (3mm or so) fit to the profile of a product. We'll make our part by RP, so no machining cost worries. I have a dumb solid of the product (actually an assembly of a few parts), so my first plan of attack was to do offset surfaces and then trim them up into a model. However, due to a lot of inside radii, I end up with self-intersecting surfaces when I try to do the offset. Any tips for this type of operation? Surfacing pitfalls to avoid? Will I just have to carefully pick my surfaces and then trim up from there? Of course, due to IP I can't post any files on this one.
Thanks!
Thanks!
-handleman, CSWP (The new, easy test)






RE: Question for Surfacing Guys
I would stick with the offsetting/trimming tactic. Even if you've got to be selective when picking surfaces to offset in order to avoid self-intersecting surfaces it will be easier (and undoubtedly faster) going this route than trying to surface up what you need. Especially so if you're not all that versed in surfacing.
You may have to generate some surface patches in areas where you just can't get an offset to work, but you'll still be better off, IMO.
RE: Question for Surfacing Guys
If you can offset major surfaces, pick clusters that make the most sense, that will offset properly. This will generate lots of individual surface bodies. Then extend edges of surfaces to past where the small intersecting problems happened previously (I'd recommend ignoring the offsetting of the small fillets for now). So the small fillets aren't included in your offsets and you can use either the Extend or Trim features to get the desired inner surface you need, then use the Cut With Surface feature to core things out.
You might even find rebuilding (instead of offsetting) some of the fill-in-the-gap stuff to be quicker. After getting your main surfaces offset, hide your solid body so you can see what you're doing. I tend to prefer the Mutual option when Trimming surfaces. You may need to use the Knit feature to make sure your surface is singular before attempting the Cut With Surface. Also, you'll probably need your surfaces to extend past the solid body in the shell hole area--so you may need to extend a flange or some such thing through the base of the part (or whichever surface will be "open" in coring out the solid) before making the cut, again, making sure it's all Knit together as a singular surface. If the surface body doesn't go past your solid stuff, SolidWorks will get confused as to the boundaries of your Cut With Surface.
Jeff Mowry
www.industrialdesignhaus.com
A people who value security over freedom will soon find they have neither.
RE: Question for Surfacing Guys
To follow up on Jeff's post, you can also try to make use of the untrim command to extend surface boundaries once you've got offsets created. It will depend on the geometry you need to create whether you untrim the interior/exterior boundaries (or both).
I used to have to do this all the time in a previous life (albeit in a different CAD package). I don't envy you. Best just to resign yourself to the fact that this will take a while to do and, depending on the quality of the geometry you're starting with, has the potential for an extremely high PITA factor.
RE: Question for Surfacing Guys
Surface features till patch holes (one will often work where the other does not):
Boundary (use existing geometry)
Surface Fill (can also use 3D sketches to create surface)
Knit to join up surfaces and hopefully produce a solid model.
Use SW 2009 if you can.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Question for Surfacing Guys
I'm thinking Insert>Part, maybe with scale, maybe an intermediate part with thickened faces... Combine with subtract...
RE: Question for Surfacing Guys
-handleman, CSWP (The new, easy test)
RE: Question for Surfacing Guys
Instead of inserting surfaces, I normally try to extrude (in context) "up to surface" or set the end condition to "offset from surface." This may or may not work depending on the geometry you are working with.
Joe
SW Office 2006 SP5.1
P4 3.0Ghz 1GB
ATI FireGL X1
RE: Question for Surfacing Guys
-b
RE: Question for Surfacing Guys
I'm with rollupswx on the scale approach. When things wont offset or thicken because it creates intersecting surfaces, surfaces that collapse on themselves, eliminates surface elements, or creates 0 radius, there is always the option of scaling the surface geometry. Its worked for me on many occasions, where for instance, I'll create a carrying case for a handheld device, where the outer surfaces of the device won't offset for the forementioned reasons.
rfus