final day: the long hard road of iterations
the two last days we’ve been working hard getting the cnc mill ready for our final presentation. it has been hard work, and we have to be honest and say that we ourselves are not thoroughly impressed by our own results.
although the cnc has gotten a lot of improvements the last couple of days:
the motor control has been moved into a much nicer housing. we found a cast away pc rack cabinet, and the cnc motor control, power supplies, switches and cables fit very nicely in there. there is even room for a cool little unix machine, should we ever get the money for that.
we added some nice distance pieces to the mill instead of our previous very bulky mount. we produced the pieces in two lengths: 20 and 40cms, so we can change the pieces if we would like to cut deeply on the z-axis
also we made a suction base for the cnc, basically a wooden box with A LOT of little holes in it. attach a vacuum cleaner to the box, and voila: you have suction. we are hoping that this suction will be enough to keep flat objects in place when milling and that pieces of cut-off material will be sucked of the milling subject, but this is yet to be tested.
in conclusion (we have to conclude now, the machine is not done, but the official DTU course is over) we can say, that we have learned a lot about mechatronics in this course. above all we have gained a lot of respect for mechanism designs and the precision of industrial grade equipment. it would have been many times easier to build this machince at DTU, but building it at halfmachine has taught us some cool DIY tricks and has forced us to be creative in relation to materials & design and to think mechanisms trough in a more pessimistic and practical way. it is unfortunate that the frame we bought used for this project was of so low quality, as we think our cnc machine could be OK for small scale projects with the current motor control, had only the frame been more reliable.
the cnc machine is operational, yes:
but in real life there is still a long way to go before this machine is useful for the purposes that we had in mind.
the list of possible improvements is as follows:
hardware:
- the z axis is simply to wobbly to do any real 3D work - we have considered changing the metal rods to hardened printer rods, but we believe, that to properly fix this, the cnc requires a complete redesign of the z-axis mechanism.
- the motor mounting unscrews it self during operation. we need better fastening of the motors.
- we never finished a safety mount which was elegant enough for daily use. we tried building one of wood, but the result was simply too bulky. glasses have gotten us through so far, but we would like to implement a acrylic “cheese bell” which fits over the cnc.
software:
- finding any proper open source (or at least cheap) CAD/CAM package has been very hard. the cam package for rhino looks promising, but we haven’t had time to go into this.
- seemingly simple tasks like transfering an illustrator file to g-code has been surprisingly difficult - we’ve gotten some results with cambam and lazycad (.ai -> .dxf -> g-code), but the workflow is tediuos and the resulting g-code has been extremely dumb; that is, lines and curves divided into very small line segments, rendering any complex pictures (including round objects) super heavy and nearly impossible to process.
mechatronic:
- our milling tools are bad: we use a dremel, which has no feedback mechanism. this means that the dremel is rotating at many thousands of RPM when not cutting, and then dramatically loosing rotational speed when touching the milling subject giving an unwanted difference in milling speed throughout the material. buying a cutting tool with feedback mechanism (or constructing our own) would allow us to cut materials that are more fragile, and materials that might melt or otherwise react in unwanted ways when approached by a cutting tool rotating too fast.
- a general feedback mechanism for the frame/cutting head position would be super nice. with no feedback, even the slightest imprecision will add up throughout a more complex milling operation and result in the final millings being more off target that necessary with our mechanical precision.
we are planning to continue working on the cnc - and so are the people at halfmachine - but first we need some holiday! check back on this blog in a month or two. there might be more news for you.
we’ve taken a lot of documentation photos and bring a little excerpt below. do check our cnc flickr photo pool for the full selection.
