Continuous Arm Windsor Chair Seat with CNC Router

This is an explanation of how I created a 3D model, and cut a Continuous Arm Windsor Chair seat with my CNC Router.  The plans I used for this seat are from Curtis Buchanan's Continuous Arm Windsor Chair.

SketchUp View on 3D Model created from plans.

Curtis's plans provide a topographic map of the seat in increments of 1/8" elevations, which I used to create a topographic map of contour lines in SketchUp. Basically, I scanned the plans with the seat elevations, and created contour lines at the designated elevation and scaled to size as seen below. Next, I used the Draw > Sandbox > From Contours tool to create a surface that covered or draped the contour lines. Unfortunately, artifacts were created by this process in the surface, and required extensive clean-up. I tried several 3rd party plug-ins, but nothing seemed to work as well as the Sandbox tools.

Contour lines of seat

After creating the model in SketchUp, I exported the data to a *.dae file (COLLADA format), and then used Autodesk FBX Converter to create a *.obj (Wavefront format) file. This OBJ file was then imported into Vectric Cut3D, and used to create the G-Code to cut the seats from a 520mm x 490mm x 50.6mm slab of Pecan/Hickory.

Vectric Cut3D rendered view of Seat Top

The project required three sets of G-Code.  One set to cut the top of the seat, followed by one to cut the gutter.  Finally, I finished the project by flipping the slab front to back and cutting the bottom.

Roughing Cut

Finishing Cut

Finishing cut and prior to cutting gutter

Adding painters tape to reduce tear out or chipping prior to cutting gutter.

Bottom

After removing the piece from the slab, it required some trimming with a router to smooth the edges and remove the tabs.

The unfinished seat prior to drilling, scrapping and sanding.

Plans for this chair as well as several others may be purchased Curtis's website, and instructional videos are also available on his You-Tube Channel - Curtis Buchanan.