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An Elliptical Windowcomments (6) January 28th, 2012 in blogs
I again attended the Colonial Williamsburg conference, Working Wood in the 18th Century. This year the theme was Furniture of George and Martha Washington, therefore presentations and demonstrations focused on Mt. Vernon. One of the presentation was by Ted Boscana, joiner and carpenter of Williamsburg. He showed the process of creating the Mount Vernon Bull's Eye Window in the west pediment, a complicated re-construction indeed.
I found the construction in SketchUp to also be a challenge. I started with a rough photo of a painting found on the Internet. It had a similar look and shape. I scanned the picture and imported to SketchUp followed by a re-sizing to an approximate full-size. I then began to layout arcs and centerlines as shown below. (It looks like I'm creating a spider web.)
Step 1: To make the ellipses, I first draw a circle and then the Scale Tool. You can see the Scale Tool's grips surrounding the circle. Grab one of the middle grips and pull horizontally to the length of the long axis. Hold the Cntl Key (Option key on the Mac) while doing this re-shaping as it will cause the elongation to work symmetrically around the original circle's center.
Step 2: I located centerlines for spokes and assumed that they would intersect with the center of the ellipses.
Step 3: Since the window is symmetrical about two axes, I began working only on a quartile as shown below.
Step 4: Around the centerlines I began sizing the individual pieces in width.
Step 5: All of the pieces in the window are shaped as a typical window muntin cross-section. I created a shape as shown below and it provides for a rabbeted back to accommodate the small window glass segments.
Step 6: In preparation for shaping the pieces, I separated the window faces into the following components as follows. Then I gave all the pieces a common thickness with the Push/Pull Tool.
Step 7: The outer ring is shaped with only half the molding shape. The illustration below shows the setup for doing a Follow Me with this half-profile shape on the inner edge. The profile needs to be perpendicular to the path, so I've extended the path slightly on the red axis. Also, I've extended the path on the other end, to insure that the Follow Me goes beyond the end of the outer ring.
Step 8: After the Follow Me, I executed an Intersection with everything selected. Here is the result after clean-up.
Step 9: Perform the Follow Me and Intersection with all the component parts as shown.
Step 10: I then reassembled the inner ring segments and executed another Intersection to clean-up the connections. I also "Hide" the edges at the boundary of the quartile assembly. This will prevent edges showing when I combine the four sub-assemblies.
Step 11: I created V-cut sockets for the spokes as they connect to the outer and inner rings. I also made mortise and tenon joints at both ends of the spoke connections.
Here is the result in its final assembly.
And here is a view of the back of the window with the rabbets to accommodate the glass segments.
This was not an easy execution, lots of messy intersections. I suppose that is why I wanted to try the challenge. Thanks again to Williamsburg and the Mt. Vernon staff for another interesting and valuable conference.
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Learn the art and science of designing furniture in SketchUp with Fine Woodworking's official blog. Moderated by a devoted community of woodworkers, we feature step-by-step SketchUp tutorials on designing components, downloads of pre-built 3D models of furniture parts, and news and information about the evolving world of digital furniture design.
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