In a sept 14th RepRap Post, Michael suggests the use of paper in place of a heated bed for printing, a new way to even the printing bed base with thumb screws, modified firmware for greater speed, and a “faked small nozzle” to allow better bridging and tighter plastic bonds.
We are honored to have inspired Rick at Reprap to modify his printer based in part on our design.
Details from Michael’s original post are copied below:
I made some big changes to improve 3D printing out of the standard domain of ~25% fill to 100% fill. I print almost all my parts in 100% fill, which is tricky, because if the fill is off your parts can warp inward or outward. Also, as the nozzle goes over for multiple close passes, it tends to “bunch up” or collect and dislodge previously laid down plastic. Also, full fill was very slow before.
To solve these problems, I started with the base alignment.
EVENING THE BASE:
The makergearv2 comes with a screw set with springs and many nuts to help calibrate the base. This is a great start, however, because the base is wood and wasn’t threaded, it meant that turning the screw for calibrations would squish the nuts that held the screw in position around the wood. What you could do was turn the nuts holding the springs in place, but it was very difficult to get in there and turn small screws, plus it only gave you about 100 microns of alignment space because the screw was weak. To fix the base, i tapped two pieces of hardwood with 1/4-20. This is tight enough to act as a loose lock-nut – the friction prevent dislodging from stepper vibration. Meanwhile, I upgraded to fully long springs that have about 5 times more force. Next, I use thumb screws for easy access. I am able to use a piece of paper to test the friction between the nozzle and base at Z=0, and can calibrate the whole device in seconds. Also, I applied flat glass ($2 from home depot) over the PCB and uses hot glue and two paper clamps to hold it in place. The glue needs a few heat-cool cycles to equalize (otherwise the center bows upwards about 0.2mm).
PATTERN BEGINS IN PAPER:
Next, I recognized that no matter how hard you try, sometimes getting a pattern started requires tricks, temperature changes. Instead of tricking the print to extrude more in the beginning, or modifying temperatures, I use a piece of paper clamped to the base. This allows all extrusion to embedd the paper, which sucks up the cheap chinese PLA like a sponge (even at 185 C). Also, because the paper absorbs by wicking/surface tension, it keeps the nozzle head extremely clean and it doesn’t bunch up or collect old prints for the first layer or two.
MODIFY FIRMWARE (5:1 SPRINTER)
The basic idea of 3D printer now is keep the nozzle cool, and print slowly, otherwise you’ll pickup and distort previous prints. To prevent this, and ooze from forming, you also retract the filament, and Z step up and then back down to prevent ramming into/crossing over a perimeter from the same layer. What a pain!! And so much slower. So in my design, I speed up the firmware so it accelerates very quickly – 4 times faster than the default settings. I also ramp up speed to 350mm/s between printing areas. This allows you to turn up the print speed so fast that between extrusion areas, the nozzle doesnt have time to ooze. That means if you go over an existing perimeter, it doesn’t have time to scrape it off while it is hot. It also means hotter temps are okay, and thus, welding of plastic fully. I also eliminated the temperature checks to allow the Printrun software to set the temps and the firmware ignores any settings. Also, set max speed to 350mm/s, print at 60mm/s. My default layer height is 0.1mm, and don’t worry, its FAST enough.
FAKE SMALL NOZZLE:
Use slicer 0.9.1 to tell the nozzle it is 0.4mm OR set default extrusion width to 0.4mm. This way, you get multiple passes. At low extrusion temps, the nozzle puts out a line thinner than the 0.5mm width of the nozzle. Therefore, faking a smaller distance closes the gap and allows better overhang formation.