Here’s Part 2 in my endless thread on printing with LW-PLA …
So now the important question is what did it take to get good quality prints using LW-PLA on the X1C? Just trying to “tweak up” the standard Bambu PLA presets didn’t work. And trying to “copy + paste” some settings I found online (see Part 1) flopped for me. So that left good old basic printer calibration work - what I was trying to avoid! But the end result was definitely worth it. Note that this post looks at the main printer settings first - Nozzle Temp, Flow Ratio, and Speed (aka Max Volumetric Speed). I”ll add one last post to look at a “grab bag” of other settings and tips that affected my LW-PLA prints.
A quick sidebar on using LW-PLA. Since LW-PLA “foams” and expands during printing, it is absolutely horrible at dealing with seams, retractions, Z hop, and head travel. It strings like nobody’s business, leaves blobs and surface “pimples” all over the place and makes a total mess during printing! The whole calibration and settings game is about trying to maximize the weight savings while minimizing this junk. It also turns out that the design files themselves can make a huge difference. Design files that are optimized for LW-PLA (like the plane files from Eclipson, 3DLabPrint, Planeprint and others) print almost in a single continuous extrusion with minimal retractions and head travels (it’s kind of like vase mode).
I really wanted to just jump right into printing, so I first tried copying some of the settings from the LW-PLA posts that I referenced in Part 1 that looked like they should work with the X1C. The results weren’t good - the test print had very weak wall strength, poor layer and structural adhesion, and lots of surface imperfections. It was obviously under extruded. Here are the main settings I used for my first “failed” test (with a 0.4mm nozzle):
- Layer Height = 0.25mm (recommended by Eclipson)
- Nozzle Temp = 240
- Flow Ratio = 0.42
- Max Volumetric Speed = 5
- Speed = Silent (I didn’t change any other Speed settings)
Even though the results weren’t good, I did learn a lot about which settings would need to be optimized. And some of these initial settings did end up being “golden” for me (like the Max Volumetric Speed). Here is a “Before-After” comparison of this “first test” vs my final settings [LW-PLA "Before & After" Settings - Album on Imgur]
Since the lazy way didn’t work out (when does it ever?), I did some more research and found a great post on the ColorFabb site that laid out a step-by-step process to identify optimal calibration settings for LW-PLA [HOW TO PRINT WITH LW-PLA]. Note that they use ColorFabb filament and a Prusa for their example, but the basic process should absolutely give you the right settings for your Bambu and whatever LW-PLA you want to use! The calibration process uses a Perimeter Test Cube to identify the 2 key settings:
- Step 1 - Find the Nozzle Temp that creates the most “foaming expansion”. This will give the lowest weight.
- Step 2 - Find the Flow Ratio that gives the most accurate size after the filament has expanded (“foamed”).
OK we have to go down another rabbit trail … There is one other critical setting that is affecting this whole process - print speed! I saw a lot of detailed recommendations for Speed settings on the Bambu for LW-PLA. I also saw some mentions to just use the “Silent” speed default. Finally I stumbled across Max Volumetric Speed (which I had ignorantly never heard of) which acts like a “master throttle” over all the filament related Speed settings (at least that’s my simple understanding). A lot of the posts I read agreed on a MVS setting of 5 mm3/sec for LW-PLA (this is set in the Filament settings). Which with a 0.4mm nozzle and 0.25mm layer height equals 50mm/sec for the Speed (if I did the math right). And with that one simple setting I never messed with any of the other Speed settings to get the results I was looking for with LW-PLA. I just print on Standard Speed (one less thing to remember) since the MVS is “throttling” all the other filament related print speed settings. I expect you absolutely could manually fine tune all the detailed Speed settings to increase the print speed on the Bambu. But I also saw a lot of recommendations for LW-PLA speed settings less than this, so I’m pretty comfortable with how this is working for me. And it’s simple …
How does this “2 Step Calibration Process” actually work?
- Step 1: To do the Nozzle Temp test, it doesn’t really matter if you have the Flow Ratio “dialed in” or not. That gets tweaked in Step 2. But I had some “inside info” for my X1C from my original (failed) print test. I knew that a Flow Ratio of 0.42 was going to under extrude. So I bumped it to 0.50 for the Nozzle Temp test. I printed off a set of test cubes starting at 220C and went up in 10C increments while measuring the wall thickness with a micrometer. Once I passed 250C the wall thickness started going back down, so I stopped. My best “foaming expansion” nozzle temp was at 250C - that gave the thickest walls on the text cube.
- Step 2: So I had the optimal Nozzle Temp to give me the most “foaming expansion”. Now I needed the optimal Flow Ratio to get the “foamed” walls to the right dimensional size. For things like RC plane designs, dimensional accuracy is important so parts fit together. I printed out another set of test cubes at varying Flow Ratios (all at 250C). The wall thickness needed to match the line width / nozzle size (0.42mm default - basically the nozzle width). I found a Flow Ratio of 0.50 gave a 0.42mm wall thickness on the test cube, and a Flow Ratio of 0.55 gave a 0.44mm thickness. I decided to go with 0.55 to trade off a little weight savings for slightly more structural strength. This was just my call - I could absolutely have stuck with 0.50 and gotten the same print quality at a little less weight. Also be aware I’ve seen posts from others that are successfully printing at lower Flow Ratios (down to .35) based on their printers, speeds, etc.
Here is a look at the Nozzle Temp and Flow Ratio test cubes [LW-PLA Test Cubes - Album on Imgur]
OK with my new Nozzle Temp (250C), Flow Ratio (0.55), and favorite MVS (5) in hand, I tried another wing section test print. And this time it came out great! Not perfect - but really good. The print was very clean and structurally sound. It looked like I might actually be able to get this LW-PLA stuff to work! But there were still some small problems, so it was time for some “fine tuning”. And that’s where the next (and final!) post picks up …