Issue 4 – July 2002     SolidWorks User Group

Next Meeting: Tue 6 Aug 2002   -   1800            -     byo food / drink

PDL Conference Centre        14 Hazeldean Road, Christchurch,  NZ

Presentation Agenda:

1.       Linsay Armstrong, Intercad trouble-shooter-about-town, will offer insights about some of the fundamentals of core and cavity modelling

2.     Iain Wickens, just back from Level II training in Auckland, learned quite a few useful things, some everyday, some exotic. He's going to "show and tell".

3.     Informal discussions

Should be a good night for everyone. It's part of the grand plan to revisit basic activities from time to time – it's what we spend a big chunk of our day doing.

Last meeting:

1) Rapid Prototyping Presentation and Q&A

Derek Bishop, of Stratatec Rapid Prototyping Services, gave us an overview of Rapid Prototyping technologies, and some specifics about current and upcoming Rapid Prototyping services they offer. This was a fascinating look at the various processes, for most of which Derek was able to show us samples. In particular, Stratatec currently provides parts in ABS using Stratasys' Fused Deposition Modelling process, in which a nozzle lays down the polymer, like a glue-gun in the hands of a cake decorator.

Derek explained that the company is presently negotiating the purchase of a 3D printer, a "Quadra" from Objet Industries, a start-up RP machine-builder in Israel (see web address below). In this process, an ink-jet methodology is employed to deposit very fine layers of polymer.

No single technology has all the answers, and it was clear that you first need to decide on the material characteristics you require, then select the process which can supply those characteristics, to a finish and accuracy which most closely approach what you need, at a price you can afford.

It was also evident that a constant watch needs to be kept on developments. Cost of parts is still on a steep downslope, but new processes tend to start out more limited in the range of materials they can offer.

Derek can be reached at http://www.stratatec.co.nz

There is an interesting assessment of leading technologies (by a user of all three) on the http://www.2objet.com website in downloadable pdf form

There is quite a good summary of how various technologies actually work at

http://www.me.psu.edu/lamancusa/rapidpro/primer/chapter2.htm

2) SolidWorks Surfacing. Presentation and Q&A

Iain McMillan, a PhD student at Canterbury University, provided a highly informative run-through of some tutorial resources from the SolidWorks World 2002 Reseller and User conference. Edward Eaton, an extremely knowledgeable user of SolidWorks who specialises in lofts and sweeps on difficult shapes, may be known to those familiar with the "Solid Solutions" magazine. Others may have seen his posts on the comp.cad.solidworks usenet forum at Google Groups. (click on "Groups" on your Google search page) The time and high-quality intellectual engagement he lavishly donates to help perfect strangers grapple with horrible modelling challenges is mind-boggling. You haven't met a truly altruistic person until you've met a truly altruistic American.

His website at www.prodesignsrv.com has a number of PowerPoint-based tutorials (including the couple that Iain touched on) available for free download. A number of CanSWUG members took advantage of Iain's kind offer to burn them a CD of these and other tutorials he'd pulled off the web.

Iain started by explaining how SolidWorks treats surfaces and solids, revealing that so-called solid modellers are in fact surface modellers, which automate and (largely) hide from the user the fact that they are actually using surfaces to define solids. These surfaces, wherever possible, are infinite, and the software keeps track of boundaries within each surface to define the solid edges.

It further keeps track of which side of each patch faces "inwards", in order to differentiate a cavity from a boss, essential for solid modelling.

He explained the important distinctions between analytic and algorithmic surfaces. While the former are simple geometric primitives, the latter, essentially spline based, freeform shapes, cannot be extrapolated by the software beyond the user-defined boundaries. Hence an "extrude up to surface" will happily infer where to terminate in the first category, even though the analytic surface in question is not big enough or is out of position. Features extruded up to a freeform surface must however fall within the boundaries of the terminating surface, or they will fail.

Iain went on to show how these fundamental differences affect how design intent gets captured into any model. Identical looking simple parts, where one face is spline-based, can respond differently when, say, filleted, depending on whether the software can determine how that face should be extended.

The analytic/algorithmic distinction also helps explain why we can happily sweep a cut along some model edges but not others.

In trickier modelling, it becomes more crucial. Often a given result can be achieved either with solids or with surfaces, but some tasks are very difficult to achieve smoothly –  bordering on impossible – unless we resort to surfaces. Moreover, the modelling overhead for the software can be greatly reduced if we do the latter, because if we feed it solids it has to define surfaces to get the job done, whereas if we "cut to the chase", we can save it having to create and keep track of maybe five redundant surfaces and at least twice that many associated boundaries (to create a notional solid) for every functional surface.

Examples of surface solutions to intractable problems Iain showed us included cunning ways to get smooth results along centre seams of symmetrical freeform parts, methods and respective merits for constructing the same object with either surfaces or solids, and ways of using new features such as "replace surface" to dramatically simplify adding features to a freeform face.

Iain had clearly thought carefully about how to pitch this material, and I know I'm not alone in thinking he struck a superb balance.

If, like me, you went home at the end of the night thinking "I could never do this", be reassured: the group exists to cater to all levels, both as regards modelling and presentational prowess. It's a sure bet that every member has at least one worthwhile presentation in them, and by the time we get around everyone once, this will doubtless have increased many-fold.

Enhancement requests: Followup

The results from our session and voting were sent to and discussed with the Asia Pacific Technical Manager for SolidWorks Corporation, Mr Ba-Thong Phan, who rolled out SolidWorks 2001+ at the session which seeded this user group.

I've had a response from Ba-Thong. Several of our items will be addressed in the next release, and several more have been included in the list for future action.

 I'm not at liberty to print which items these are, as SolidWorks have a policy of not venturing down the vapourware path by facilitating the pre-selling of features the software does not yet offer. Nevertheless, if anyone has a personal interest, he's happy for the information to be passed verbally to user group members at the next meeting, provided once again that it doesn't make it into print (eg usenet, emails etc). Sounds reasonable.

Thanks again to all those who participated and voted.
It wouldn't make much difference if we didn't do it, but it would sure make a hell of a difference if nobody did!

3) Tips of the month: Planes

1)      Want multiple offset planes at an even spacing? You can now do them all in one hit. An innocuous and cryptic icon has recently snuck into the "Offset Planes" creation dialogue box. Hover patiently over said icon with Tooltips on, and it will reveal its true identity: "Number of Planes to Create".

2)    It often seems attractive to use a "Plane through point". Problem: midpoints and endpoints of lines are relatively fragile – they can easily shift, say if a fillet is added later. The plane will move without notification, and the person making the change may not realise. Where possible, use a line rather than a point to define a plane.

3)    It is often necessary to "stand up" a plane normal to a construction plane, like a bookend, but not necessarily square across the 'shelf' (pursuing the bookend analogy).
In this instance, use "Plane at Angle", but think of it as "Perpendicular plane through (hinge) line", by setting the "Angle" to 90 degrees. The hinge line is simply drawn on the construction plane as a sketch, at the desired angle.
This seems to me one of the most useful applications of "Plane at Angle", and 90 degrees would, to me, be a more sensible default than the current 45.

Contact committee at:

Iain Wicken iwickens@nz.schneider-electric.com
Mladen Meduric mladen.meduric@hamjet.co.nz

Andrew Troup a.troup@amadablam.net  (items for Newsletter)