Underextrusion

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The firmware of the printer controls the speed of the Bondtech extruder gears rotation (among other things) – that’s how the printer pushes the filament out of the nozzle.

Each profile in the PrusaSlicer app contains settings that determine how much filament the 3D printer should extrude. However, because the 3D printer does not provide any feedback on how much filament actually leaves the nozzle, it may be that less or more filament than the firmware expects. If that happens, you may notice gaps between (or in) layers.

 

The most reliable way to test whether your printer extrudes an incorrect amount of filament is to print a simple 20 mm high cube with at least 3 solid layers at the top and at the bottom. You can tweak these settings in PrusaSlicer “Print Settings” tab. At the top of the cube, make sure that the 3 top layers are firmly connected. If there are gaps between the three layers, then it means the extruder is not pushing the right amount of filament.

The first thing to do is to check if you have the nozzle properly attached and it’s not clogged. Unscrew the nozzle and use the supplied needle to make sure that the filament passes smoothly.

Cold Pull (MK2/S/2.5/3/S) – is a technique that allows you to clean your printer’s nozzle from the remaining material that is stuck or “ burnt” in the nozzle after previous prints. The procedure is simple: preheat the nozzle to 260°, then insert the filament manually into the extruder and push it until it flows out of the nozzle and until it pushes the previous filament out completely. Disable the heating and  let the nozzle temperature drop to the room temperature. Then heat it again to +/- 90- 100°. Once you reach this temperature, pull the filament out out of the extruder using pliers and a reasonable amount of force. Then you should see remnants of the previous materials or dirt that have settled in the nozzle at the tip of the filament that has been pulled out. You can repeat this procedure several times to achieve better results. 

Cold Pull (MINI) – the procedure is the same as with the MKx product family above. However, with the MINI, before you pull the filament out of the nozzle, you need to remove the PTFE tube first. Use the bundled spanner to remove the locking nut at the top of the extruder, pull the PTFE tube away and then pull out the filament. You can repeat this procedure several times to achieve better results.

Clean Bondtech (i3 MKx printers only) – It is recommended to use a lithium based grease (e.g from conrad.de or amazon.com/super-lube) or a PTFE grease. However, be careful not to overuse it, as it tends to accumulate dust particles over time. This procedure should be done roughly every 3-6 months, depending on how often you are using the printer. For instance, if you are printing 24/7, you should check the gears more frequently. The procedure is simple: Open the Extruder idler. You can see how to do it in our assembly manuals, simply undo STEP 27 in E-axis assembly chapter. Clear any left-over filament, rust or dust with a brush and inspect both gears.

Put some lithium grease on the Bondtech extruder gear teeth. You can also inspect the Needle bearings that are inside. However, these do not need any special care, just make sure that both of them are properly inserted.

Clean the extruder gears (Original Prusa MINI) – Open the top extruder door and remove any filament scraps and/or dirt from the gear. Use compressed air to clean the gear. You can also open the extruder idler and clean the second gear. Simply loosen the screw right under the loading PTFE tube until the door on the other side of the extruder fully unlock. Open them and clean the inner part of the extruder.

Check cooling – make sure that cooling works properly as it should and that you do not have a fan blocked by, for example, a piece of filament from any of the previous prints.

Keep your filament dry, free of moisture because damp filaments have a negative impact on printing.

Do not overheat the enclosure if you use it, it can result in these issues as well.

50um layer height can be too much for your filament and can cause jamming of the filament. We recommend using only high quality filaments, such as Prusament.

Miniatures – Printing miniatures (such as 28mm figures) can be a bit of a challenge on an FDM printer, but it can be done. It’s good to place multiple objects next to each other, so the nozzle doesn’t stay in one place for too long. We recommend printing miniatures with 100% infill. You can also try decreasing the perimeter printing speed to 32-35 mm/s and to 22-25 mm/s for external perimeters. The optimal layer height is 0.07 in PrusaSlicer settings)

Hardened nozzle – if you are using a hardened nozzle, try replacing the nozzle with the original 4mm nozzle that you have received with the printer and see if it makes a difference.