A few Thursdays back, we started a second version of our CNC frame, for a semi-automated pick-n-place machine. We'd already started one frame, but decided, in the end, that it didn't really follow the idea of small-scale, desktop manufacturing. It was a beast of a thing - really heavy, cumbersome to carry around, took up loads of room, and had massive stepper motors flying up and down the gantry.
A second version followed, a few weeks back, made from some metal brackets from B&Q and a few sheets of Dibond. It was easy enough to put together, but the overall finish wasn't very impressive. It doesn't matter how smooth your linear rails are, and how much you grease the rods - if the rails aren't perfectly parallel, you're going to get binding somewhere!
Steve pretty much said as much last week - as we were discussing the poor performance of CNC frame V2.0 he suggested that the only way to get a decent CNC frame, ensuring everything was square and parallel, was to CNC cut one. Our desktop CNC is still waiting to be set up, so that was out. But we do have a fully functional laser cutter. That's just a CNC with a laser instead of router isn't it?
It took about 6 hours, to design, cut, fit, re-design, re-cut, refit, scrap-and-start-again and finally produce our laser-cut mdf CNC frame. The first lot of shapes came out quite quckly.
The y-axis was up and running in next to no time.
This is actually the fourth version, strictly speaking - there was an earlier mdf version that we aborted after about two hours, because making space for the steppers and everything else was just getting really difficult.
So in this version, the end piece (where the y-axis rails fit in) extends 33.5mm beyond the base plate. This allows us to put a small nema14 stepper motor under the actual frame (you can just see the pulley attached to it, on the left hand side of the bed).
The uprights are reinforced by gluing two-similar shaped pieces side-by-side. The inner piece has slots for the x-axis cross-member, while on one of the uprights, we made a little box to house another nema14 stepper motor.
The x-axis gantry, ready for fixing over the y-axis travelling bed. At this stage, the gantry is independent of the other part of the CNC. We've yet to decide how to fix the two pieces together. We're even toying with the idea of being able to dismantle the overhead x-axis (by unbolting the "feet" of the gantry from a baseplate) to make storage a little easier.
For the x-axis, a single linear bearing will sit on the one rail with skate bearings fixed on the top and bottom. The skate bearings will run along the back piece, to stop the main bearing from rotating as it travels left-to-right across the gantry.
The final design is just over the size of an A4 sheet of mdf. This means the device will be small enough to be portable, as well as comfortable to use on a desktop, without taking over half of the room, when in operation!
Next time we'll be fitting the x-axis rail and fixing belts to the motors to actually get something moving!