I've not found a good 3D-THD lisp file. In ACAD 3D, a swept profile follows a 3D-Pline Helix, starting at a plane normal to the starting segment of the 3D Pline, and sized in a conventional way using major & minor thd dias, thread profile, etc.
A short-cut method I've used with great success is to simply create an accurate profile of the entire thd, and revolve it around the CL of the thd'd hole, or the CL of the bolt. High degrees of accuracy can be achieved with this method, especially with the nature of the data we're forwarding to the machine shop and the FAB shop, in the extracted detail drawings. You lose the fact that the model as displayed isn't a true helix, but you lose visibility of the helix anyway, at any normal zoom, and the resulting visual representation of this thd'd feature is easily as "realistic" as the best you'd get with any helical representation.
Another benefit is that the "weight" of a simple revolved profile is far less than a fully developed helical calculation. Even the uncredited lisp routine offered above warns that "...this may take awhile." Now don't get me wrong , the routine runs well and delivers on its promise, but the system and model "price" is a bit high for my tastes.
Another method I've used with great success is to accurately model the hole at the minor dia of the THD (or the bolt at the "Major"), with hole-in and hole-out treatments represented (Chamfers, clean-ups, reliefs, etc). I'll sometimes take this a step farther by assigning the ID of the "THD" surface with some standardized color adopted to mean "Threaded Hole" at a glance. No thread form (beyond the in- and out- treatments) is represented. This is the "Lightest" method I've found for representing thd'd holes in a part, and represents the thd'd hole well at ANY zoom ! A color convention I've used has the ID surface the same "color" as the rest of the part, just one shade-step darker. Doesn't sound like much, but you'd be surprised at how well threaded holes stand out from un-threaded holes in shaded and even rendered representations. Or you can pick a standard "Threaded Hole Color".
A nearly "Inventor"-like approach is to attach a bit-map of properly developed thread form to the I-D surface, for "Renders". You'd be pleased with the results!
Mention that all of this is better handled by S.W. is right on. The translated model even works very well. Basic 3D ACAD works VERY WELL within its limits, and often returns much more value for the investment, UNTIL you determine it no longer meets your productivity needs. BTW, have any of you seen Inventor? I was AMUSED at how they handle this question !!! Take a close look at the Inventor-9 cross section of any UNC or UNF threaded Hole. Which thd "hand" is being represented by a Rt-Hand thd'd hole properly set up ?!?
Anyway, good luck !
C. Fee
