Over the last few years my Lulzbot AO-100 has been good to me, and has served as my workhorse. Unfortunately, as with every machine, heavy use equates to wear and tear. At just over 3-years old my AO-100 is starting to show its age, and its tolerances are not as tight as they once were. This morning I took about an hour to work on re-calibrating the printer with the main focus on proper Z-axis layer-height.

I have been noticing the decline in print quality for some time now, but chose to ignore it as I have not had the time to properly service the printer in several months. Early this morning, I began a print for a friend that had elements in it that needed to be within a millimeter or so of its specified dimension. I know my AO-100 prints about 0.5mm over the sliced dimension, so I chose to print the part in ABS, assuming that its shrinkage would account for the overage, or at least most of it. I use Voltivo Excelfil ABS almost exclusively due to its consistency in diameter, its high quality composition, and its rich pigmentation. I also find that my ABS prints tend to shrink less with Excelfil, over cheaper Ebay / Amazon specials.

I haven’t printed ABS in almost 6 months, and have slowly tweaked the printer to print PLA fairly well, but I had not accounted for how different PLA and ABS print on an aging printer. I used my PLA slic3r settings to slice the print, only adjusting for the print temperature, raising the extruder from 200c to 225c, while the heated bed rose from 65c to 105c. I left the layer height set at 0.20mm, with the first layer being 65% of the normal layer height. The speed was set at 60mm/sec for almost everything except for small radii which was set at 40mm/sec. Likewise the first layers speed was set to 65% of the normal layer speed.





As you can see from the image above, these settings worked great with PLA on my slightly worn (closing in on 200lbs of filament now) AO-100, but unfortunately that did not turn out to be the case with ABS. I do not have any photos I can share of the failed print due to NDA’s and such, but I did snap some photos of the calibration prints I ran to get things adjusted to spec for ABS. As you can tell from the image below, the first calibration print (we’ll call it baseline) did not resemble anything remotely like the Nickel Calibration print that it should have.

I witnessed the extruder’s nozzle actually dragging through the previous layer. This helped me understand where I should begin my troubleshooting. The first thing I wanted to look at was my bed’s Zero Height to the extruder’s nozzle tip. After letting the tip heat up (The nozzle expands, so you should always check the zero with a hot nozzle.) I checked the zero with a piece of paper. This showed me that the nozzle to print bed height was just a little too low, and I adjusted my z axis height to fix the issue. To set the height I like to fold a piece of common printer paper in half, and the thickness of the two sheets is what I set the z-axis height to.

With that fixed I moved on to changing some settings in slic3r. I felt that 0.20mm was too small for my aging printer and ABS, so I raised the layer height to 0.35mm. I then ran a test print. As you can see from the image below, the print actually looks a lot better, but it still has a long way to go.

I made a note in my notebook about the previous adjustments, and adjusted the first layer flow rate from 150% to 200%.I mainly did this because I noticed that the first layer was not sticking to the bed very well anymore. When the extrusion did stick, it was the right height, and had a sort of “squished tube” look, which is what I was looking for. With the flow rate adjusted, I ran another test print. The results were again positive, and as you can see in the image below, I was inching ever closer to an acceptable print result.

There was some blobbing, and the layers were not as squished as I would have liked them to be, so I opened slicer again and made some adjustments. The first thing I did was change the layer height to 0.30mm, and set the extruder’s temperature to 220c.

This would hopefully help get the layer adhesion where I wanted it to be as well as reduce the blobs.

After running a test print, you can see that this worked well, and the print was within what I deemed to be an acceptable quality range. I knew I could still tweak out a little more performance and quality, so I set to work on trying to tighten the printers tolerances up a little more. The first thing I did was tighten both the X and Y axis belts, and then I took a few minutes to clean and lubricate the smooth rods that these axis ride on. Finally I added a drop of silicone oil to each of the idler bearings that the belts rotate on. This made the printer move a lot more freely, and reduced almost all of the noise that the printer had been making.

As you can see from the printer above, this did make a difference in the print quality, and I was happy with the result. I did go back into slicer and bump the extruder temperature to 223c as I seemed like the printer was having a hard time keeping up with the thermal mass that was passing through its extruder. I would see the nozzel drop to 218c from time to time during the print. Raising it to 223c ensured that it stayed at or above 220c at all times. The image below shows the final result. While it is still not perfect, I am calling it close enough until I get the time to replace the ball-joint bearings with proper LM8LUU liner bearings.

The image below shows the different prints, from the first to the last, and as you can tell, the end result is quite nice for a 3-year old printer with almost 200lbs of plastic ran through it. When it was all said and done, I had maybe 30-45 minutes into tweaking the printer, and I am confident that it will keep this calibration for several months.