I've brought this reprap to its working limits in a couple of different ways over the last few weeks, firstly with a bespoke drill-guide that I made in a similar way to the dremel cutting kit only super-sized so as to allow a cheap hammer drill to make nicely perpendicular holes in the absence of a drill press.
A trouble with this print is its huge width compared to the narrow surface area actually in contact with the print surface, which meant that, being a PLA prototype, it could barely adhere to the kapton-taped surface strongly enough to stay down. When some overhanging edges started to curl up slightly, the resulting light collisions with the extruder head caused the wider of two parts to start lifting up off the printbed with an audible crack. I found a quick fix to keep that part in place before the whole surface dislodged.
|Bulldog clips and small allen keys were handy, so they held the part down.|
There is a slight complication in the build volume with this triangular-prism shaped frame, depending upon how the extruder is fitted; normally the greatest available Z-height is clearly limited by when the tallest part of the extruder reaches the top bars, or in my case when part of the extruder motor reaches the control-board mounting plate.
When starting to test I learned a simple lesson about the J-Head Mk.IV hot-end: don't ever forget to turn on a cooling fan when running PLA through it.
|Result of no cooling: molten PLA worked its way up to plug the heat barrier.|
|That black set-screw I think is about M8 size, and is a clever way of keeping the sleeve compressed while having a gap for filament to pass through.|
So I gave printing on cardboard another try, this time trying to print a plant-holding part of my rotary hydroponics kit, but something else went wrong in the first layer when it seemed that the hot-end couldn't stay up at melting temperature.
|Adhesion to inside-of-cereal-box cardboard was initially great until this.|
|This nearly-new wire-wound heating resistor that came installed with the new hot-end somehow ruptured under normal operating conditions. 'W21 5PS' is printed on the opposite side.|
There was still another problem with fitting my old heating resistor though.
|It didn't fit.|
|But a bit of aluminium foil quickly solved that.|
First I tried a wide part that would test the warping problem that I had with paper. For this I used a z-motor bracket from Prusa's Mendel iteration 2 repository, aligned flat along the build plate. I quickly saw again something else that I needed to improve in my printer:
|Overhanging corners of PLA start to curl up slightly during printing.|
Although I clearly needed to add some cooling to improve the quality of slight overhangs in PLA, at least the bottom surface warp wasn't bad.
|Pretty good actually, very near parallel.|
My solution to cooling was to hook up a fan that I'd salvaged from the case of an old discarded mac computer with some spare wire and old bolt-on PLA bushings.
|Fan in foreground with another z-motor bracket cooling down.|
|So good that it would fit right away without any reaming.|
|A large print of my custom switchbox design.|
|Gregfrost's filament-guiding extruder idler ('guidler') broke between layers, allowing the filament to slip off the extruder biting point, so I designed and uploaded a reinforced version.|
|Warp was pretty bad this time.|
|My electronics mounting board is now about as crowded as it can get.|
After testing wide-object warp (the badly warped box seemed to be more due to adhesion loss than flexibility in the cardboard), I wanted to check out how well a tall object would print, so I placed a couple of the same motor brackets in their usual vertical alignment along with a few bar clamps to also see how well small things would do here.
|I also set slic3r to code in a line of skirt material around each object individually rather than around the whole print at the start, hoping that this might help to stop edges peeling up.|
The small bar-clamps turned out fine, but the motor brackets not so well due to there being enough flexibility in the cardboard for them to get knocked back and forth by the extruder head.
|These definitely weren't usable straight off the printer.|
|Oh, and a pulley.|
That worked exceptionally well, so I did some more.
|These were still great, even though the parts spanned a lot of the cardboard area, and they pop off cleanly and easily by simply bending the card after printing.|
|Bottom surfaces are almost perfectly flat too, with a very shiny finish.|
I've also seen people on the reprap IRC saying that they have successfully printed ABS onto a glass surface by using a thin layer of PVA (a common wood glue, which forms a water-soluble biodegradable polymer that has also been used as removable support material in dual-extrusion printers). This is great since it means that people can stop using polyimide as a print surface, since it is clearly unsustainable as a thermoset that loses its 'stick' in a number of months. There is a slight paradox there though since ABS as our main heat-resistant prototyping material is itself an unsustainable feedstock as we don't have any way to produce it that doesn't use fossil oil. This I'll be looking at solving through over-engineering soon - by sand-casting parts in recycled aluminium from PLA forms.
After all that, I've finally prepared a couple of test pieces to see how strong the mounting points in my wind turbine design can be, meanwhile it looks like the studding&nuts used as cheap leadscrews on my z-axis are finally wearing out badly from friction. I'll update with details when I have some results from strength tests, as this post has become long enough and I have a few other things to be doing first.