This project came about as a result of my propensity to never throw away parts that were designed to or can be adapted to move electrons. I am also very interested in mechatronics and motor control in general and so it was all but certain that over time I would have accumulated enough of various discarded data storage devices because they are so cleverly combining parts of both mechanics and electronics. We live in world filled with discarded devices that only a few years ago were the stuff of science fiction. I always feel bad about the discarded yesterday’s technology and it gives me an extra kick to have it re-purposed for today’s needs.
Fast forward to 2011. I was perusing Instructables.com one day and came across a project description called Pocket Laser Engraver by Groover. it made me realise that in the years I was delaying my floppy-based project, DVD drives, even the writing variety, have become so common that they can be very easily found everywhere and, unlike the floppy, they have the laser diode needed for the cutting tool. As a result of my switching the gears towards a DVD-based CNC setup, I made a few tiny CNC models that could be cut on a DVD-based cutter.
The experience with the aeroplane models illustrated just how small of a working surface DVD linear slide allows (and a 5.25″ floppy would have the same limitations). 1.5″x1.5″ (38mmx38mm) is a very small area and, to fit in it, you have to drop small details – the scale I used was 1:212 which makes the planes only just barely recognisable. Given my particular interest in airspace models, I could sure use at least one longer axis to cut long parts of wings and the fuselage. On the other hand, the broken/discarded DVD drives are so cheap that adding one to the project does not really increase the cost all that much. If you are sourcing yours from eBay, they are usually sold in packs of 3 or more, to save on shipping. Buying them individually, even when offered, would make no sense to you due to prohibitive shipping costs anyway.
This is how the idea of two DVD drive linear slides working in tandem providing twice the length of the X axis came about. The video above shows the two DVD linear slides bolted together through the laser diode sleds. The control circuitry is designed to send each of the STEP signals coming out of the CNC control software to the alternating stepper drivers, causing only one stepper to move in each step but allowing the top platform (which the Y axis, not pictured, rides on) to travel twice the distance – a whopping 3.0″!
3″ x 1.5″ cutting area that this setup allows is still obviously very small. However, it represents a 100% increase in the X axis length and so the added complexity of the control circuit looked justifiable to me. The next posts in this series will present the control circuit, other design considerations and the results of the test cuts made on this DVD CNC laser cutter.