In search of Elegance #4: Surfacing. Without the headache

Published 19 October 2009

Posted by Al Dean

Article tagged with: design, delcam, powershape, in search of elegance, surfacing, intelligent surfacing, hybrid modelling

Basic construction of a Viking sailing ship. Boat design is one of the most elegant forms in the world of engineering. Simple, efficient and timeless (and when I say timeless, I mean, since 1500 BC). Image courtesy of the good folks at Vikingskip.com

Here’s something I was reminded of recently on a trip to see the team at Delcam (in their HQ quarters, a scant 15 miles from my home, rather than 8,000 miles away in Korea this time). If you’re not familiar with it’s solutions, Delcam has a huge range of technology which often solves real, live problems faced in the heady world of design and manufacture, rather than, as some vendors choose, creating solutions looking for problems. While there’s much elegance in many areas of Delcam’s offering, one thing lept out at me – and that’s how it’s flagship modelling system handles surface creation.

Surfacing is a complex business. From first principles, when you’re trying to create sculpted, complex forms, you’re looking at an inherently more complex workflow than when working with prismatic features. the geometry is more complex, so the creation of it is going to be more complex, right?

Traditionally, yes. Absolutely.

Surfacing requires that you first build a network of curves and the precise form of those are controlled by not only the form you want to create, but how you want to create it. There are many types of surfaces. Planar surfaces are flat and the simplest. Then you have four sided surfaces, n-sided, bi-rail surfaces, extrudes, lofted surfaces, swept surfaces, blends, flanges, fillets. Filleting in itself is a very complex art depending on your form requirements. If you’re working to corners, then you’re looking at trying to merge three or more surfaces converging on a single point and at that point, you might want different fillets, different set-back value.

All in all, its a complex and often daunting prospect – particularly for those that have learned their trade-craft using mainstream, solid modelling applications. Knowing what forms you’re aiming for is essential to create curves (often referred to as wires), before you even get to actually creating a surface.

Delcam’s PowerShape has been on the market for about ten years or so and the company has been through revision after revision to give its users a set of tools that allow you to work with complex geometry, fix it, prepare it for manufacture That’s given it a perspective that is only shared by a handful of vendors. Delcam has a set of tools that are used by a community that’s both a) demanding (as they need flawless data – which begets flawless tool forms) and b) very used to dealing with crappy third party data. These are the people that take crappy data and turn it into a manufacturable item – something that requires highly efficient tools.

Perhaps the perfect example of this is how PowerShape handles surface creation. As we’ve discussed, you’re often facing multiple decisions about what curves to create, then what exact type of surface you want to create, before you even start to think about creating any geometry. What Delcam has developed is Smart Surfacer and it takes many of these decisions out of your hands – or at least, gives you a helping hand.

Basically, you create the curve network you want, then invoke the Smart Surfacer command. This presents a simple dialog box. With this active, you then start to select the geometry, either from curves or from existing surface edges. The system inspects your selections, looks at the types of surfaces it can create, then presents you with the best guess is has for the best type of surface you could create based on that selection. As you add more geometry to the selection, it reevaluates the choice and switches the surface type and displays a preview.

1. Take this simple geometry set – two circles and a connecting arc.

2. Select the smaller circle and you get a planar fill surface.

3.Add in the connecting arc to the selection and it’ll switch to a drive Curve, to push the arc around the circle.

4. Adding in the large circle maintains a Drive Curve, but runs it between the two circles, using the arc as the Drive Curve.

Here’s another example

1: Rectangle, helix, circle. – selecting the rectangle gives you a planar surface.

2: Adding the helix into the selection gets you a drive curve that’s very similar to a swept feature.

3: Adding the circle in switches the Drive Curve to push between two forms, creating a smooth transition.

Of course, these are pretty simplistic demonstrations for the purposes of getting the concepts across, but the usefulness and the simplicity of the tool should be clear. Quite often you’re not dealing with singular surfaces such as these, but rather, dealing with the complexity of trying to finish up that set of surfaces, to squeeze that final last few in that tie together the whole form, the points where form quality is won or lost – and that’s exactly where this tool comes into its own. Rather you having to rework other surfaces in the set to patch in that final surface, the system can find the optimum solution and present it to you for inspection and fine tuning. there are also more manual tools avialable from the command, such as the Composite Curve creator, which can assist greatly when you have multiple, disjointed surfaces meeting at one area.

PowerShape’s Smart Surfacer is a perfect example of what I’m looking for in this search – it’s a deceptively simple tool that collects together best practice, knowledge and experience of dealing with some of the worse geometry known to man and presenting it in a tool that adds that intelligence in an unobtrusive manner, while giving you the freedom to dive in and edit things manually if needs be.

PowerShape-E is avialable for free, to play with at your leisure at www.powershape-e.com – I’d recommend doing so to anyone with a passing interest in complex shape description.

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