Hotend jamming

I am having problems extruding any material (using PLA). Each time I heat the nozzle up to temp (180C, verified w/an IR gun) I get some plastic bubbling out of the tip for a little bit, but then it stops. If I try to push the filament through (manually or using the extruder stepper) nothing comes out, and I can feel that it has jammed.

Currently using an all metal hot end. When heating the hotend with the fan off, I get jams all the way up to the brass fitting where the filament enters the hot end. Heating while the fan is on full blast prevents those jams, but I am still getting a jam in the threaded rod that separates the cooling fins and the tip. I had a plastic tube in the rod to help guide the filament, but it burned up. Then I made the threaded rod out of a heat-resistant glass-like material (don't remember the name) with the idea that it would keep all the heat down in the tip, but got a jam in the same place.

I'm thinking it is something where the fan and the heater cartridge are conflicting with each other; where the heater heats up the plastic while the fan cools it into a lumpy solid.

I would appreciate any solutions or ideas you can offer. Thank you!

The "plastic" tube inside was probably PTFE. It's not just a guide. It acts as a heat barrier and also creates pressure inside to keep the melted filament from flowing backwards.

Check the temp of the "cold end" with the IR gun with your fan on and while off.

The PTFE tube should not have burned up under normal operating temperatures.

To check if your hot end is clogged. Remove filament (you may need to disassemble the hot end), cut off end of filament, heat hot end to operating temp, and push filament through in constant motion. This will prevent the heat from transferring up the filament too fast. If no flow out the nozzle, you have a clog.

Lower your temp to 160 at start and increase slowly until it's flowing.

What is your nozzle size? The smaller it is, the more pressure you will need inside to create flow.

A picture of your hot end and extruder would help.

There may also not be enough or too much spacing between your heater block and cooling fins.

Thank you for the reply! My nozzle diameter is 0.3mm. The cold end of the cooling fins is about 60C with the fan off (and using the glass rod). I think the reason the PTFE tube originally burned up was a problem with the thermistor reading way too low.

I ran the hotend with the fan off and the glass rod, and it actually extruded for a bit before jamming again.

I don't have a picture, but the spacing between the heater block and cooling fins is about 0.25inches. Is that what it should be? Also, could the problem be me trying to force too much filament through the nozzle at a time? I think I may be pushing in x volume of filament per time, but the nozzle only lets out y volume per time, where y is smaller than x. What do you think? Thanks!

1/4 inch sounds about right. The inside diameter might just be a tight fit for the filament you have. I hear lubricating with veg. oil helps keep PLA flowing.

Depending on the ability of your thermistor to read temperature and the firmware you are using, when your PLA starts flowing it will start cooling the hot end. The faster you extrude the colder your heater gets. Your firmware is trying to keep up with this rapid cooling and may be overheating before it turns off again.

I'll have to get some vegetable oil tomorrow to try out.

I am using an ID of 2.1mm for 1.75mm filament - is that about right?

Hadn't thought about the PLA cooling the hotend - the temperature reading does oscillate about 5-7C on either side when extruding, so that is probably it. It also smokes a good amount, even when the readings (thermistor and IR gun) are only at 180-190C. Does that mean it is overheating inside somewhere even though the surface temps are okay?

I think that hat creep is melting the plastic so it folds into itself and can't get into the hot end. You should probably replace that pfte or find a way to cool it better.

That smoking is probably stream. If it smells bad it's burning plastic.

I'm sure that 2.1mm is for the PTFE tubing. It needs to be a considerably tighter fit down the nozzle to create the pressure you need. Without building up pressure inside the hot end, you won't be able to force the plastic through a 0.5mm or 0.3mm hole.

How tight? I have a set of drills and some more glass material, so I can make another rod. Would 1.85mm work, or does it need to be tighter than that?

That depends on the style of hot end you are using. You can either contact the manufacturer or find a schematic drawing that will detail the tolerances. Most of them have a wiki how to page that will detail the construction.

This sounds like the OP broke his E3D-clone's stainless steel heat break (the heart of the E3D), and tried to cobble a replacement part together out of glass. If so, there's no point in trying to troubleshoot the jamming until the original stainless steel heat break has been replaced with an exact stainless replica...inside and outside. If the cold end of the cooling fins are hitting 60C with PLA, it is no wonder a plug is forming above the substitute heat break.....