Does your printer stop extruding on the first layer or maybe later in a print? Does your machine print inconsistently with missing cross-sections? Does it fail on intricate cross-sections? If your extruder gear ever grinds or slips or your filament, you’ll want to read below!
The above mentioned jams and partial clogs are often from a combination of heat creep and/or restricted flow (material going into hot end exceeds the material coming out of the nozzle). This effect is worsened by all-metal hot ends, high torque extruder gears, small nozzles/layers, and excessive retraction, but you can find success with bit of finesse and fine tuning.
To get more reliable results with PLA printing, consider the following:
- Heat treat (crystallize) your PLA filament. This sharpens the melting point and better resists heat creep and compaction with more maintained stiffness to higher temperatures. To heat treat, preheat your oven to a stable temperature with no glowing heating elements. You can also shield any radiant energy with Aluminum foil. Make sure your filament is wrapped tight (like with plastic wrap as delivered from Proto-pasta) and bake at 200-225F for 3+ hours. More time (overnight for example) is okay. Don’t be alarmed if your spool glue or filament (composites or non-impact modified versions) become more brittle. Handle with extra care.
- Don't like the result or idea of heat treating, then oiling is a good alternative and supplement. A thin film of mineral or vegetable oil on the filament surface is a more of a bandage, but makes the material slippery enough to keep compacted filament moving inside a sticky hot end. A little oil goes a long way. I well coat my filament before inserting into the hot end, and then maintain with oil dabbed on a paper towel taped around my filament between the drive gear and filament spool. This is highly effective! You won't believe the difference if you have flow issues!!!
- Want to further relieve flow restriction for more reliable printing? Select a high print temperature (as much as 230C) and/or reduce speed to make your material more liquid (less viscous). Decrease your flow rate to force less material into the hot end and/or increase your nozzle size to let more material out. For example, reduce flow from 100 to 80% or replace your 0.4 mm nozzle with a 0.6 mm. Pushing harder (with increased flow rate) usually does not make more material come out of the nozzle and instead more readily results in a jam. Often decreasing the flow actually creates more consistent extrusion.
- Can't get past the first layer? Choose a relatively large first layer gap as too small of a distance, like too small of a nozzle, restricts flow and can cause filament compaction leading to jams. A high temperature for the first layer and slow speed (with cold blue tape, dried PVA slurry like made with Elmers Disappearing Purple Glue, or smooth surfaces heated up to 70C) are good for adhesion, but can create a worst case scenario for heat creep. This is why step 1 and 2 so important in finding a process window and avoiding much frustration!
If you’ve had grinding, make sure the extruder gear is clean and clear for a fresh start without compounding failure. A large first layer distance and appropriate flow rate/nozzle size are key. FLOW INTO THE HOT END MUST EQUAL FLOW COMING OUT OF THE NOZZLE. PUSHING HARDER AND FASTER DOES NOT ALWAYS MAKE MORE MATERIAL COME OUT. FLOW IS LIMITED!
If you are still getting jamming, please make sure your nozzle set temperature is being maintained. It's possible you have a poor temperature regulation or are feeding the filament faster than your hot end can heat it. In some cases, your layer cooling fan can also be cooling your nozzle so you may need to decrease your fan speed or turn it off entirely for a better result. Finally, beware of aggressive retraction. Filament likes to move one direction so minimize or turn off retraction for more reliable printing.
Hopefully, you find this informative and helpful in wrangling your hot end for non-stop, reliable printing. Success can be yours in 2017!