# 3D Modeling Special Interest Group – August 2019

In this session, we showed how Working Planes can be used to model objects in the right place to start with. We also covered how to use the Extrude Along Path command to make footings and slab thickenings, and how to calculate their volume so that you know what the fill or hard fill is.

Topics Covered:

• 00:27    We started by constructing a small building because we wanted to experiment with Working Planes. You can save them and create, for example, a Working Plane for each face of a building if you need to. We wanted to add a chimney to our building. The challenge was how to place the chimney correctly after modeling it off to the side, or how we could model it in place, because the Working Plane was the sloping roof—objects are created perpendicular to the Working Plane, but we needed the chimney to be perpendicular to the ground, not the roof. One option was to draw the rectangle for our chimney in Top/Plan view, elevate it to the desired height using the Move 3D command and then, using the Project tool, to bring the shape down to meet the roof. The Project tool even extended the chimney so that it was at the correct angle where it met the roof.
• 11:45    The next challenge was to fabricate an object in Top/Plan view, because that seemed easiest, and then to rotate the piece to fit into our model. We demonstrated how to accomplish this and then how to make the same object in place. But, in fact, it was very difficult for us to orient ourselves to the Working Plane so that we could made the shape how we wanted—we made all kinds of weird shapes instead! A hybrid symbol won’t tilt to match a sloping Working Plane, but if it’s just a 3D symbol, it will. We played with this concept a bit by experimenting with a 3D car.
• 30:03    We used the Extrude Along Path command to add a footing to a foundation slab after creating the profile of our footing and using the Extract tool to create the perimeter of the slab. Next, we wanted to add slab thickening—we again used the Extrude Along Path command. We discussed how to go about calculating the fill. We could extract a surface at a time underneath our slab, but not all three—the underside of the slab, the shape of the footing, and the shape of the slab thickening—at the same time. An easier way was to draw a rectangle from corner to corner, extrude it to the full depth of the foundation and use the Subtract Solids command to get a shape that matched the negative space under the foundation, which equaled the amount of our fill. We added a hatch to the fill so that it would show up as hard fill in a section or elevation, and went through the steps for calculating the shape’s volume. The only downside to this method for creating footings is that, if you need to change the size of your slab, the footing and slab thickening don’t update automatically—but there are a lot of practical uses for these objects!

3D Modeling August 2019

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