All the tools we’ve used to design the air hockey paddle so far have enabled AutoCAD to maintain the integrity of the sub-objects. Even after we combined the cylinders, sphere, and cone into a composite solid using Boolean operations (union and subtract) we could still access and edit the primitive properties by pressing the CTRL key. We could continue to modify those properties (in addition to the chamfer and fillet properties) even after we added chamfers and fillets to the model. There are some tools, however, that cause the model to lose that editing capability. You can save a lot of editing time if you avoid those tools until later in the design process. For example, I ultimately want the air hockey paddle to be a thin shell rather than a solid mass and AutoCAD has a Shell tool that is perfect for this type of operation.
Unfortunately, the Shell tool strips the individual components (cylinder, sphere, cone, fillet, etc) of their intelligence. For example, when I press the CTRL key and click on the tall cylinder before using the Shell tool, AutoCAD knows it’s a cylinder and displays the appropriate grips. When I click on the same object after using the Shell tool, AutoCAD treats it as a face with limited editing capability.
It’s not a big deal if those sub-objects already have the perfect values. But, in conceptual design, that’s rarely the case. You want the ability to edit those values for as long as possible. Nevertheless, the Shell tool is handy for creating thin-walled objects such as the air hockey paddle. So, being satisfied with the design thus far, I’ll perform the shell operation.
The Shell tool is available on the Solid Editing panel of the Home tab. You’ll probably have to open the flyout toolbar to find it. The Shell tools is actually an option within the SOLIDEDIT command but it’s kind of buried (you’ll first need to choose the Body option). If you like to use the keyboard you might be tempted to type SHELL. That’s not what you want. The SHELL command (unlike the Shell option of the SOLIDEDIT command) has been in AutoCAD for as long as I can remember and it launches an OS window. I make that mistake sometimes (too often) but the brief flashback to DOS always makes me laugh.
After you successfully launch the right Shell tool, you’re prompted to select a 3D solid object and then you’re prompted to remove faces. “Remove faces” doesn’t mean it’s going to remove faces from the object. It’s giving the option to exclude faces from the shell operation. For example, when I performed a shell on the air hockey paddle, I selected the circular face at the bottom of the cylinder resulting in an open bottom.
If I had “removed” the cylindrical face instead, it would look like this:
If I had removed the circular and the cylindrical faces, it would look like this:
If you don’t select any faces (just press Enter to end the selection set), the outside of the model won’t look any different but it will be hollowed out. After you specify which, if any, faces to remove from the shell operation, you must enter the shell offset distance. I entered a distance of 1.5 for the air hockey paddle.
Key Concept:
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Creating a 3D shell.
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