# My 3D printer hotend always jams

I've just built my first 3D printer. It uses a Bowden setup.

When I try to print the extruder starts fine, but after a few seconds the extruder motor start skipping and the nozzle is jammed.

I tried a cold pull, but it didn't help. I removed the PTFE tube and tried to push the filament with my hand, it works but at the start I need the push harder but after it flows fine. But if I reinstall the Bowden setup, it works fine for a few minutes, but after a few seconds it starts again.

Note I am using silver PLA at 200-205 °C. I tried to raise the temperature to 215 °C, but it also jammed, and the filament what after I pushed out was black (it is a new hotend and I never used black filament before), like it was burned (if it is possible).

• Welcome to 3dPrinting.SE! What temperature are you using at your extruder? What filament type (ie: PLA)? – Pᴀᴜʟsᴛᴇʀ2 Jan 2 '20 at 23:51

Extruder clogging is, at its root, a matter of too much backpressure at the hotend. There are a number of more specific causes, but it very simply comes down to the fact that the printer cannot feed the filament through the hotend as fast as the extruder is pushing it in.

Things to check, pretty much in the order they should be checked/performed for a brand-new printer:

• Extruder stepper calibration. With new printers based on RepRap firmware (Enders, Prusas, pretty much any printer in the \$200-\$400 range these days), one of the first things you have to do after assembly is to calibrate your E-stepper (the motor that drives filament through the extruder). The printer is given commands based on millimeters of movement, including the feeding of filament, and it has to translate those into finite steps of the motors. If those steps don't actually move the extruder or the filament as much as expected, the printer will behave poorly, including clogging. E-stepper calibration is pretty easy, especially on Bowden extruders; you basically disconnect the Bowden tube at either end, load filament through the stepper, cut it off flush with the end of the tube or the coupling, then tell the printer to extrude 100 mm of filament. Cut it off flush again and measure, and if it's not 100 mm, look for a command beginning with M92 in your printer configuration (it can be in the settings of your actual printer or a configuration script in your slicer software that gets tacked on to the front of the G-code files generated for use with that printer), and adjust the value you see after the E in that command by multiplying it by 100, then dividing by the millimeters of filament actually extruded in the test. Rinse and repeat until the printer is feeding the amount of fil you tell it to.
• Bed height/leveling. This may not sound like it has anything to do with extruder clogs, but in truth, if your extruder is too close to the print bed at any point during the first layer, it can very easily clog the extruder by not allowing enough material to flow out the nozzle to keep up with what's being fed in. Bed leveling is a key step in print prep, and every printer behaves best with subtle changes to the bed leveling procedure. My guess is that you need to re-level for a slightly higher "zero-Z" above the build plate. If you're using the sheet-of-paper method, either use a thicker piece of paper, or go for less friction as you pass the paper between the nozzle and build plate.
• Nozzle diameter settings. The standard nozzle tip diameter is 0.4 mm, however there are others. Your slicer probably expects the standard diameter as a default, so if you're running a 0.3, 0.2 or 0.1 mm nozzle for finer detail, the slicer has to be told that so it can adjust the filament feed rate. Otherwise it'll be jamming up to 16 times as much filament into that hotend as it should be. This isn't likely to be your problem but it's something to check; most extruder nozzles these days have the tip diameter engraved or pressed into the side of the nozzle, and if yours is unlabeled, try heading to the local music store and buying a single 0.013" guitar string (typically sold as a high E for acoustics). If that wire end easily fits through the extruder nozzle, you have a 0.4 mm, if it does not, it's something smaller.
• Extruder clog/obstruction. That guitar string I mentioned makes a really good extruder cleaner. Just feed it through the extruder tip and gently push it up through the hotend till it pops out the top of the extruder, then feed it back and forth a bit to "floss" the extruder tip, cleaning out any minor carbon buildup. If you can't feed the wire completely through the extruder body from either direction, that's probably your problem, and fixes range anywhere from a little more pressure with the wire, to a narrow drill bit carving out the obstruction, up to removing the entire heat block from the printer, putting it on or in something that won't burn, and blasting it with a soldering torch to burn out the obstruction, followed (after letting it cool) by a bath in some acetone to dissolve any remaining gunk.
• Gunked-up extruder hobb. The toothed wheel attached to the extruder stepper is called the "hobb" (you may hear it called a gear, but it's really not one as it doesn't mesh with another gear). As the printer feeds filament, especially if you've had jamming problems, the hobb's teeth will fill with shavings from the filament it feeds through. This can cause the hobb to slip against the filament, which not only reduces the pressure of the filament being pushed through the extruder, it accelerates the accumulation of gunk on the hobb. A short blast of canned air is usually all you need to clean the hobb; if it still looks pretty caked up, a toothbrush will sort it out. While you're at it, check the idler to be sure it's still spinning freely.
• Filament type/brand/age. You mentioned it's "silver PLA"; the silver stuff I have is actually a "silk PLA" product, that sheathes the PLA in a jacket of another plastic (often PET) for that high-gloss appearance. These kinds of filaments can be very temperamental, as can filaments with glitter or fiber aggregate in them (also common in metallic fil colors). You have to have the printer settings dialed in just right, and some of these products just don't work well at all in some printers. Try getting some very basic, brand-name PLA filament like Hatchbox, ColorFabb, MatterHackers, MakerBot, etc, in a good primary color (avoid black or white; the color saturation affects how easily the stuff extrudes at a given temp), no silk finish or other modification. If that prints well, the suspect becomes the silver fil.
• Extruder temperature. You're printing at 200-205 °C, which is usually good, but if you're getting problems, the first thing to do with PLA is to try printing cooler, not hotter. Case in point, getting PLA too hot can cause it to fully melt and drizzle out (vacating the extruder and causing it to overheat the fil further up, jamming the melt tube), it can gum up (directly clogging the extruder nozzle), and it can carbonize (as you see it doing at 215). If you're already flirting with burning your PLA at 10 degrees hotter, you are probably running too hot. Try backing off to 195 or 190 and see if that helps any.
• Very complete answer! Welcome to 3DPrinting.SE! – 0scar Jan 3 '20 at 21:19
• I set it all, but it did the same thing. When it starts the print with the outer edge (brim) it prints with fast speed it works fine but, when it starts the actual object -20mm calibration cube- it prints slowly and nearly instantly the nozzle jammed, and the extruder can't feed the filament and start skipping. – VLKI Jan 5 '20 at 14:00
• @VLKI - It sounds like you are either using a variable print speed setting, or you have widely varying speed settings between line types. What these settings are called and how you can set them depend on the slicer software, but long story short you'll want to keep the extruder moving at as constant a speed as you can. – KeithS Jan 6 '20 at 15:32

I had a very similar problem with my printer, and it turned out that the bowden tube was not fully inserted into the hotend. The hotend is bored out to a very close fit to the tube. I had inserted it about a half inch, until it stopped, but it had only gone in to the top of the hotend.

After I inserted the bowden tube fully, my clogging issue stopped.

You can insert a toothpick or something and measure the depth, then mark the tube at the same measurement to ensure it gets fully inserted.

It is useful to diagnose your problem if you provide more information, specifically what material you are using and what temperature you are using on your hot end.

Even without the above information, it is likely that the hot end temperature is too low. At a low setting, the filament in the nozzle will soften, perhaps even melt as deeply as needed to be extruded, but as new filament is provided by the extruder motor, it also cools the heater block.

By increasing the temperature, you're ensuring there is sufficient thermal energy to handle the incoming cold material.

It would be useful to increase your nozzle temperature by 5°C for each test. Despite matching your controller's temperature to the manufacturer's specification, you can not be certain that the temperature at the nozzle and heat block are what you have programmed.

• I use silver PLA with 200-205 C. I tried to raise the temperature to 215 C, but it also jammed, and the filament what after I pushed out was black( it is a new hotend and I never use black filament before), like it was burned (if it is possible). – VLKI Jan 3 '20 at 10:38