3D printers have become more robust and precise with each passing generation, but they’re still far from immune to the occasional glitch that ruins complex projects. This is especially frustrating when it’s a long print — the last thing you want to see after 24 hours (or more) of work is the printer extruding into thin air, a few centimeters above the part. Fortunately, recovering a failed 3D print is not impossible. All it takes is a few measurements, some G-Code manipulation, and a whole lot of patience.
The printer prints in the air
A speck of debris clogging the nozzle, a power outage, an accident near the machine (liquids, pets, kids… you never know), and dozens of other reasons can sabotage a 3D print. One of the worst situations is finding the printer doing “air printing” — that is, “the printer prints in the air” — after several hours, but beyond the initial shock, all is not lost.
At the end of the day, 3D printing is a game of coordinates: if you can pinpoint the last point where the print was correct, you can continue from there. That’s easier said than done, though. The CNC Kitchen channel published a video detailing some of the options available to recover a failed 3D print, and the first recommendation is to keep the bed hot so the part doesn’t lose its position.
Learn how to recover a failed 3D print
- Remove all remnants of the last layer that didn’t finish printing. You need a clean, even surface to continue.
- Measure the height of the part. This is a crucial step, and you’ll likely need two or more calipers depending on the shape of your project. The measurement must be perpendicular, from the bed to the last completed layer. If you don’t have calipers, you can use two or more metal rulers and take multiple measurements to reduce error.
- Another approach is to use the part’s geometric features to get measurements. Open the G-Code in a viewer (your slicer should have one), then compare layer by layer to find the exact point.
- Logically, the printer itself can determine the part’s height with a little help. Have the printer return to its home position on the Z axis without hitting or moving the part. Clean the nozzle and place it exactly over the last printed layer. The printer’s screen should display the Z value, or you can send the M114 command to the controller for a reading. Comparing all three methods, the margin of error in this example was a tenth of a millimeter (90.7–90.8 mm).
- When resuming, some users prefer to continue from the failed layer, but CNC Kitchen suggests continuing with “the last layer + the layer height defined in the print” to avoid double-extrusion. In this case, that’s 90.8 mm + 0.2 mm layer, for a total of 91 mm.
- Time to modify the G-Code. This is where most people give up, but G-Code is easy to interpret once you understand the basic commands. Essentially, you’re looking for the layer-change command (in this example, G1 Z91.000) and then you must delete everything between that line and the printer initialization. Save the modified file and load it into the printer again. The print should continue without issue, but keep an eye on it.
What if we can’t return to the Z-axis home?
Once again, measuring the part’s height is critical. The difference is that when editing the G-Code, you’ll also need to delete the G28 command (which means "home all"), because you’ll be defining the start position manually. This is done with tools like Pronterface, which let us fool the printer’s controller. First, home the X and Y axes (G28 XY), then enter M211 S0 to disable software limits, place the nozzle over the last layer, and enter G92 Z(last layer) to set Z. Restart the print, always watching closely. If something goes wrong, turn off the printer, clean up, and try again.
What if the part came off the bed?
If the part lost adhesion, your best bet is to measure its height, load the original model into your favorite slicer, "cut" off the printed portion, continue with the rest in a new print, and then glue the two halves together. There are excellent adhesives for 3D prints, and if your measurement is good, the seam will be nearly invisible.
Recovering a failed 3D print: In summary
No doubt about it: recovering a failed 3D print is complicated, time-consuming, and you’ll need to adapt these tips to your specific combination of software, part, and printer… but it’s not impossible. Anything that saves us time and filament is welcome.
CNC Kitchen on YouTube: Click here
