At Bow Wood, we are constantly striving to push our limits and as a team, work to find innovative solutions to complex problems. The Connaught School project gave us another chance to do just that. The architect that came up with the design for the feature wall at the Connaught School sent us some CAD files for a very intricate tree (picture 1) and said, “Can you make a 12 ft wide, 16 ft tall version of this?”
We looked at the files, calculated that it would take several hours of meticulous CNC operations and careful spray painting, and responded with, “Yes we can”!
The tree was to be cut out of ½ inch MDF, painted black, and fastened to a wall. Essentially it would be a 3-dimensional silhouette to grab more attention than a painting would on an otherwise empty school wall.
So how hard can it be? Surely all the router has to do is follow the specified path? That’s what we thought, too. We began to prepare the DXF file for our CNC router and resolved that it consisted of 72 lines and 2,055 splines. Broken down further, it made a total of 15,323 operations for the router to perform, many of which were literally impossible and would have to be altered or removed: hundreds of zero-length spans, pockets with surface areas less than 1mm2, various looping intersections, and so on. Clearly this was not something a human being had sketched, nor was it designed for CNC machining!
In addition to the toolpath hiccups, the design was so awesome in detail that there would have been very little MDF left to give the tree any strength. The finished product would have been highly fragile and attempting to lift and install it would be a formidable task.
But problems have solutions! We worked with the architect to simplify the CAD file, removing dozens of tiny pockets to increase the strength of the skeleton and reduce machining complications. The tree was enlarged by 300% to the full 192 square feet, a 4 inch square grid pattern was added to be etched across the entire surface, and we set to work with a new file. (Picture 2)
To cut the tree, we needed to make 6 different DXFs, each 4 feet wide and 8 feet tall (picture 3). All the branches on each 4×8 sheet had to be scrutinized to ensure there would not be any pieces (picture 4) overhanging the edges (blue rectangles in picture 2). Once the twigs had been rearranged to fit within the boundaries and a few engineering tweaks to the layer names had been made, the files were router-ready.
Upon ‘nesting’ the design on the machine it was discovered that there were multiple minute 90-degree direction changes on the toolpath which were too minuscule to have been picked up by the human eye in the initial editing (picture 5). The router would stop and lift up, unable to go on. And so began a long exercise that stretched late into the night, deleting the tiny lines and recreating a straight toolpath in each instance. As we completed each 4×8 DXF, we sent it off to be cut while we worked on the next one.
At long last things went in our favour. The tree cut out beautifully and fit together on the floor like a jig-saw puzzle (pics 6-end). It was painted black with an oil-based spray paint, left to dry overnight, and installed the next morning at the Connaught School. The school staff were very favourably impressed, commenting that they might like a smaller one to go beside it and fill some more empty space on the wall…
… Send us the PO!