Remember when I said silver PLA covered up printing imperfections?
I meant it.
TechPaladin Printing
New colors!
I just got in two lovely new five pound rolls of Ultimachine PLA, one in silver, and the other in delicious translucent blue. I suspected this would be the case, but it’s amazing how much any color that’s not shiny white masks minor print issues. These cubes, for example, were both printed with the exact same settings, one right after the other, and look how the difference in the smoothness of their walls:
The white PLA really brings out the slight misalignment; with silver, it’s nearly imperceptible. I have plans to print my giant Star Destroyer in the silver PLA as soon as I’m finished with the model. I’m 95% done, but as usual the last part is always the hardest when you just need to finish something.
In the meantime, I managed to print out one of these beautiful spiral lightbulb sculptures in transparent blue PLA. For the most part, it printed very nicely, without too many strings, all things considered. This made me happy because it’s a very challenging print.
In the process I learned an interesting lesson: With Sprinter (I don’t know about others), if you try to print an object taller than the maximum height you’ve set in firmware, your Z-stage will simply stop rising once it hits that height, but X, Y, and the extruder will happily keep going. I hit my maximum height on the lightbulb sculpture when the nozzle was about 5 mm from the top of the print, so as a result, it dumped a ton of plastic on the apex in a very unsightly manner:
But the pre-set value of 100mm for the maximum height was too conservative; I can get 115 or so with ease, and 125 is possible if the extruder carriage doesn’t move too far to the right or left when it reaches the top. After increasing the Z-maximum in firmware, I printed another and the top came out much nicer:
Here’s the final piece, sitting on my desk:
The quest for perfect layer alignment
It turns out that my Prusa’s layer alignment only looks perfect when I print objects without straight walls. Here’s an example that tipped me off that something was quite wrong:
The print on the right looks reasonably okay, layer-wise. The one on the left is another story. So I asked the ever-helpful forum and got lots of advice. First off, tighten the belts and slow down to 20 mm/sec for perimeters. Done:
Better, but not perfect yet. You can still see the jagged corners, which display the poor alignment. I found that one of the two threaded rods used for moving the extruder gantry up and down was slightly bent; replacing it with a straight one yielded this much better-looking print:
The lighting is slightly on my side here, and in person, there’s still a minor alignment problem in some places. You can still kind of see it on the rightmost tower; see how the edge is a bit bumpy in places? I’m pretty sure that most of the remaining misalignment is caused by the fact that I’m driving precision timing belts with decidedly non-precision printed pulleys made on my Thing-O-Matic. I probably could have produced better examples had I known at the time how important these would turn out to be. Figuring any part I could print at this stage would be inherently limited in its precision, I went ahead and ordered some manufactured ones that I can guarantee will be perfect. When you’re troubleshooting an engineering issue like this, it’s handy to be able to count certain things out; using perfect pulleys will at least allow me to eliminate them as the source of the trouble should the issues persist or only slightly diminish.
They should arrive in a few days, and at that point we’ll see if I’m right and they make a difference.
Replicatorg!
I managed to get Replicatorg working with my Prusa tonight. In some ways it was easier than I thought it was going to be. Here’s what you need to know:
- Upgrade to the latest Replicatorg, available at replicat.org
- Replicatorg doesn’t support SFACT, so you gotta make a real Skeinforge profile. Make one, if you don’t already have one. You can grab mine if you’d like. One important thing I had to do was disable the Export plugin’s suffix option or else Replicatorg wouldn’t automatically load in newly-created gcode files. I’ve filed a ticket for SFACT support, unlikely though it may be.
- The reprap.xml file in Replicatorg/Machines usually needs some tweaking. I needed to set the e_steps_per_mm values for each axis to match what I had configured in my firmware. The build platform size needed a few adjustments, too. You can have mine.
- Manipulating the extruder motor with the control panel doesn’t work. Since the motor behaves as expected while printing, I think it’s fair to say that this is a bug. I’ve filed a ticket.
Other than that, it pretty much all works. Now it’s back to calibrating and recalibrating with the new Skeinforge profile.
Two issues, two solutions one solution
Feeling confident, I’ve started to crank up my Prusa’s speed to see just how fast it can go. Though I’ve printed infill at 100mm/sec without problems (a bit more than twice as fast than my Thing-O-Matic ever could), I hit a snag at 45 mm/sec for perimeters when I tried to print out this nifty lightbulb sculpture:
Ew. See the blobs where the line segments meet? That base is supposed to be circular, not ribbed. Turns out the issue is that Sprinter, the firmware I chose, can’t handle fast curve interpolation. Solution: switch to the new Marlin firmware. And what a difference it made! Here are the two prints right next to one another; Sprinter on the left and Marlin on the right:
Also, I wasn’t quite right when I said before that my Z-alignment was perfect. It was excellent, but at the time not quite perfect. All that changed when I switched to fil’s excellent Z-couplings:
The advantage is that it grips both the motor shaft and the threaded rod like its life depended on it, and it keeps them both aligned to one another so that the threaded rod never rotates offset from the motor. Thanks to those new couplings and the better firmware, my prints are more gorgeous than ever.
Edit: Marlin has a significant connectivity issue that’s so far prevented me from printing anything after the first thing I tried earlier. So back to Sprinter it is. Maybe I’ll try to get Teacup working…
A better way to hold filament spools
Xnaron made an awesome filament spool holder, but after printing it, I found that it was a little too tight and that my spool wouldn’t spin freely. So I took my first real stab at using OpenSCAD and I modified the file to space out the walls a bit and slightly modify the positioning of the 608 bearings. Here’s my new version:
Now my spool spins freely and doesn’t impart any drag at all when the moving extruder carriage needs to grab some more. On a moving-extruder printer such as this one, that means slightly more consistent layer height and slightly better Z-alignment. Every little bit helps.
What an amazing machine
My Prusa is finished and printing. And man has it been a rush. I’ve been truly amazed by how my new machine required no calibration to start producing beautiful prints. Now, I didn’t say “very little calibration”, or “almost no calibration”, I said that it didn’t require any at all. Feeling ambitious, my very first print was a gigantic starfish. However, it had a peculiar problem: each layer was a little more skewed to the right than the last one:
Eventually I figured out the issue: the filament, which was mounted on a spool to the right of the printer, was hampering the extruder carriage’s leftward movement by pulling it to the right. Solution: put the filament spool behind the printer, and problem solved. So this wasn’t actually a problem with the printer itself at all! After that, I printed another starfish that looked near-perfect.
I just don’t know what to say. This printer has absolutely shattered my expectations. I was thinking that it would be my “project” printer to hack on while the Makerbot did all the work; instead it’s proven itself to operate better in almost every way.
The layer alignment is perfect. Filament reversal is perfect. There are no strings or blobs on the exterior of the pieces. I haven’t even begun to push it yet, and I’ve gotten the Prusa to print more than twice as fast as I’ve ever gotten out of the Makerbot. On top of all this, the machine is very nearly silent. My wife and I watched a movie while the Prusa was printing not ten feet away in the same room and it disappeared into the background noise. Here, see for yourself:
Compare this to the racket my Thing-O-Matic makes while printing:
My only disappointment so far has been Pronterface (not a typo, sadly), the host software that seems to be most common. It’s pretty bad. Its interface is a mess and it lacks most of the features of Replicatorg, the program that my Makerbot uses. Luckily, it doesn’t seem like too much of daunting task to get Replicatorg to work with the Prusa, so that’s going to be my big weekend task.
Final extruder calibration
I found a great way to perfectly calibrate your extruder’s e_steps_per_mm setting over at Imran’s blog. You extrude 50 mm of filament, measure how many millimeters of filament actually advanced, and then multiply your current e_steps_per_mm by (50/actual extruded amount). I did this trick and found that my extruder actually extruded 71mm! What’s going on? I followed the formula but the value of 673.83 that it gave me produced an extrusion of 71mm when I told it to do 50! It turned out that I didn’t actually measure the diameter of my hobbed bolt’s hobbling; I guessed from memory, and I was off by 2mm. I said 5mm; it was actually about 7mm; Plugging in 7mm gives 481.31 which is within 5 of the measured value. So the formula works fine if you feed it the right values. You learn something every day!
So close and yet so far away
…in Nevada, to be exact. That’s where my replacement Pololu stepper motor drivers are; unfortunately, two of the four I had turned out to be duds. So I have X and Y axes that work, and I can juggle the boards around to make the Z axis and extruder work, but I don’t have enough working drivers to run them all at once. I probably blew them out somehow, between my bad soldering and careless walking around on carpet with socks. Oh well, live and learn.
Everything is done except for these two remaining tiny little parts. And I do mean everything:
That bracket on the extruder motor is my own design. I found that the wires coming off the extruder had a tendency to get bounced and jostled around a lot as the carriage moved, so I designed a really quick-and-dirty strain relief bracket:
I’m repeating myself, but going from idea to printed part in ten minutes is really quite a pseudo-magical experience.
It all just kinda works. Truly, the last 10% of this project wound up being where 90% of the effort lay (especially since literally every wire needed to be spliced with a longer one) but it’s been so satisfying to see it all fall into place. This machine was pretty much built from hardware store components and extruded plastic. It’s basically a specialized light-duty CNC machine. The axes move with such precision… and in near-silence, too. The thrill of manipulating it is electrifying.
It’s not that I don’t already have a 3D printer, but building a RepRap literally from scratch was a very different experience compared to joining together the lasercut wood components of my Makerbot Thing-O-matic. Printing out the plastic pieces, doing it over again with better designs, selecting components one by one, waiting for the parts to trickle in, fitting everything together by hand, making mistakes and learning so much along the way—it felt less like assembling a product and more like building a mad scientist contraption. Total cost: $502, rising to $550 if you include the unnecessary purchases and broken parts that needed to be replaced. If I had to do it again, I’m positive I could shave $100-150 off the cost without breaking a sweat. For example, this Sanguinololu kit alone costs about $25 less than mine cost; this hot end is $10 cheaper, comes pre-assembled and even includes a funnier name, etc etc etc.
One more thing: there seems to be a lot of confusion out there about how to set the e_steps_per_mm variable in firmware. There’s actually a set of handy formulas that the RepRap community has come up with for setting the values on a per-motor basis. For example, here’s the formula for the extruder:
(motor steps x (1 / microstepping resolution) x (extruder gear ratio) ) / (pi x bolt diameter measured at the teeth)
Most bots will have motors with 200 steps per rotation and 1/16 microstepping resolution, and last time I checked pi hadn’t changed. The gear ratio of the herringbone gears I used in my extruder was 43/13, so I wound up with this:
(200 x (1 / (1/16)) x (43/13) ) / (3.1415927 x 5) = 673.83
You get the idea. There are more formulas for X, Y, and Z axes on the RepRap wiki.
note: the formulas on the wiki raise the micro stepping resolution to the power of -1; above, I expressed that in the form of (1 / the microstepping resolution) to aid clarity for the math-challenged.
Finally, a working power supply
It turned out that the slim HP power supply I ordered was a bust for two reasons: the biggest one was that the ATX+4 connector that plugs into my Sanguinololu was only capable of putting out 9.5 amps at 12 volts. My motors alone pull about 6 amps, which leaves only 3 or so for a future heated bed, excluding the power draw from the extruder heater. Not good enough! The other issue was more of an annoyance, but I couldn’t get the darn thing to stay on! It turned out to be a server power supply, and server power supplies need a load on the +5 volt rail to stay powered. People suggested wiring a resistor up to it, but that just seemed like a big hassle for something that wasn’t going to really be good enough anyway. Oh well, at least I can cannibalize it for parts and heavy-gauge wires.
I found a much better one for only $2 more on Newegg: an Antec NEO ECO 400C power supply. Though the price seems to have gone up to $50, it was $30 when I ordered it, and it came with a $10 off mail-in rebate. Huzzah! But more importantly, this thing is a beast: its ATX+4 connector can put out 30 amps; definitely enough.
I wired it up and turned it on and the board didn’t explode. That’s a good sign! The motors got power and everything seems to be working. Time to flash some firmware on this thing…