Friday, February 18, 2011

Toolpathing: the ninth circle of hell........

Never again will I utter the phrase "something that we can cut quickly & easily on D's awesome CNC machine....". Not because it isn't totally awesome (which it is) but because of the Tron era software required to program the toolpaths. In excess of eight hours were required at the computer to enable four hours of cutting. My hunch is that the designers of this software went on to write the federal tax code or perhaps the terms & conditions of your medical coverage. A more utterly opaque and unintuitive interface would be hard to imagine, however, hours of slow torment paid of big time. Once everything was set D's Multi-Cam fairly tore around our sheet of 6mm Russian birch ply (check the video below). We cut out our proof of concept! High fives all round! Admittedly we had a few do-overs (depth settings seemed to challenge us) and a couple of parts that failed to stick to the particle board and were thus munched by the cutting tool. At one point there was a voltage fluctuation that shut the machine down. We had to unscrew the collet, manually push the gantry back so that Jeff could crawl under the machine with a flashlight & a voltage tester, check and then reset the machine.
But it was all worth it........at just after midnight we beheld a pile of plywood parts representing the sum of our efforts so far. I have to say that my first impression was; 'is that it, did we forget some parts?' and then 'are we seriously going to make a bicycle out of this pile of scraps?' It just seemed so physically insignificant but as we started slotting the parts together the form took shape. The accuracy of the machine is impressive and all the truss frames slid with reassuring firmness into the slots. Obviously our work here has just begun. Next we meet at Jeff's shop for the long process of sanding, assembly, jigging and gluing. Some of the parts, particularly the blocks that house the bottom bracket shell and the head tube, are still to made and we haven't decided yet if we will CNC the dropouts or just cut them by hand. And don't even get me started on the steering. One of the interesting things to discover in the weeks to come will be how light & how stiff? Ideally we have a target weight of 80lbs for the fully assembled bike and currently the dry weight of the frame parts (minus glue and epoxy) is around 14lbs. If it turns out to be excessively 'noodly' then we will have to add material and re-assess how we mitigate lateral flex.

Right now we are the are the happiest wooden cargo bicycle builders this side of the Willamette......





video

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