One of the challenges that everyone who works with non-prismatic shapes (think odd, free-form organic shapes) faces is trying to determine where exactly the widest part of the geometry is from a given viewing direction.
With simple shapes, this is easy. Think of a perfect sphere. Now think of floating above the North Pole of that perfect sphere. The widest part of the sphere is the equator. A good example of this would be a ping pong ball.
Why do we care about finding this information about our parts?
Depending on how the part is going to be made, it can be a critical necessity. For instance, if the part is going to be made with a molding process, we will first have to find what is called the 'parting line'. See the example below.
In this case, the parting line is straight and flat, but you can see why we need to find it. This is where the two halves of steel are going to come together to form the cavity that the liquid material will be poured into to form the part.
This simple idea becomes much more difficult when the geometry is a complex shape that is changing directions all over the place in 3D. Consider this part, which is free-flowing and changing shape and direction in 3D all over the place.
Luckily, SOLIDWORKS comes to the rescue here and has a command that does exactly what we need!
First, let’s define some terminology:
- Pull Direction: This term comes from the tool and die industry and denotes the direction the tool (mold) will come together and pull apart to form the part. This direction sets the view angle of how we are looking at the part to determine its “widest” extents.
- Parting Line: Think of the equator on that ping pong ball. This is the widest point of the shape looking from a given direction.
- Silhouette: The outermost edge of a shape from a given viewing angle.
OK, let’s get started! The command we are going to run in SOLIDWORKS is called 'Split Line.' You can find it under the Curve icon category, or by using the pulldown text menus (INSERT > CURVE > SPLIT LINE).
When we run this command, it asks us to:
- Pick the 'Pull Direction.' This is usually a plane, but could also be a surface or an edge that indicates the direction of pull.
- Pick the surface(s) we wish to "split."
Here is the result of running the command. SOLIDWORKS has taken the complex 3D surface and split it into two separate surfaces at exactly the widest point when looking at the part from the top or bottom orthographic views.
The goal of doing a command like this is to eventually use the split line to help us form the mold that will make the part (but that’s another blog post!).
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Written by Mack Rasmussen
Mack Rasmussen is the Technical Director at Alignex, Inc. It’s rare for Mack to have a spare moment between leading Alignex’s team of application engineers and supporting our sales team, but when he does, you’ll most likely find this avid sportsman in the outdoors—skiing with his son, camping, fishing or hunting.