1st Quarter student, Steve smiles while contently working on MED 149 exercises. Isn't Steve starting to look like a real drafter?
Saturday, December 9, 2006
Developments
In Descriptive Geometry II we work through a series of concepts to learn how to find the "developments" and "intersections" of different surfaces and solids. A "development" is a flat representation of a three dimensional solid that when folded together portrays the solid object. Developments are especially useful for design sheet metal ducting. Cardboard box manufacturers will also use developments to determine the flat patterns for their specialty boxes.
The example above shows a pyramid shaped greeting card. When the seam is "cut", the flat representation of the greeting card is seen. MED 149 teaches us how to create these flat representations through projection methods.
The figure shown comes directly from one our MED 149 problems. We are asked to draw the given views of the form and develop the lateral surfaces.
The given views, a circle in the top view and a triangle with a radial cut removed in the front view are drawn. The circle in the top view is divided into 24 equal divisions. Construction lines are then projected down into the front view.
The line from the point of the cone (triangle) to point 1 is the ONLY true length line available to us. Fortunately this is all we need to determine the radius of our development. This radius can be seen in development view, and will represent the object line except where the cutout occurs. Small radial marks representing the distance between the equal divisions in the top view are transferred to the development view to located their corresponding points.
While not shown, lines from the intersection points of the radial cut at 7, 8, 9, and 9a would be projected across the front view. Where they intersect the true length line formed by point 1 and the point of the cone gives us the true length for each of these segments. This information can be transferred to the development, as shown using circles whose radii represent those lengths. Connecting the points from the cutout with an irregular curve or in CAD, a spline, shows us the flat representation of the cutout.
This is a very quick and dirty explanation for this development, but hopefully it will give you a bit of an idea for how it's created. We'll definitely be going over this information more thoroughly during Winter quarter.
The figure shown comes directly from one our MED 149 problems. We are asked to draw the given views of the form and develop the lateral surfaces.
The given views, a circle in the top view and a triangle with a radial cut removed in the front view are drawn. The circle in the top view is divided into 24 equal divisions. Construction lines are then projected down into the front view.
The line from the point of the cone (triangle) to point 1 is the ONLY true length line available to us. Fortunately this is all we need to determine the radius of our development. This radius can be seen in development view, and will represent the object line except where the cutout occurs. Small radial marks representing the distance between the equal divisions in the top view are transferred to the development view to located their corresponding points.
While not shown, lines from the intersection points of the radial cut at 7, 8, 9, and 9a would be projected across the front view. Where they intersect the true length line formed by point 1 and the point of the cone gives us the true length for each of these segments. This information can be transferred to the development, as shown using circles whose radii represent those lengths. Connecting the points from the cutout with an irregular curve or in CAD, a spline, shows us the flat representation of the cutout.
This is a very quick and dirty explanation for this development, but hopefully it will give you a bit of an idea for how it's created. We'll definitely be going over this information more thoroughly during Winter quarter.
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