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Hot-end jamming

Posted by shawnc 
Hot-end jamming
June 04, 2015 04:48PM
Hi, I'm new to the forum and 3D printing in general. I'm doing a research project and learning as I go.

I suspect hot-end jamming is a common problem but didn't find many threads about it using the search function, so here goes:

Here is my setup:

I've tried some advice found here:

Background
  • I followed all Zego instructions to calibrate the machine without issues, including setting the z-zero

First clog
  • Printing at 170-190 degrees celsius (recommended range from the Zego documentation and Pronterface GUI)
  • Using recommended settings in Pronterface 100 mm/min at various lengths less than 50 mm
  • No fan
  • There was a blockage that caused the filament to coil and harden, which prevented it from extruding or reversing past the blockage.
  • I dismantled the nozzle and removed the jammed pieces

Second Clog
  • Printing at 230-240 degrees celsius (MakerBot recommended setting) with fan
  • I managed to print about 10 slices of a 25 mm cube (G-code attached, following the test print instructions), however the filament became more and more uneven and eventually stopped coming out
  • When the filament started struggling I lowered the speed, which helped for a while, before fully blocking (couldn't extrude, or reverse past a certain point)
  • After dismantling the nozzle, there is no knot or coil like last time, only the filament is jammed along the line

Summary
  • I'm not sure what's causing the blockage
  • I suspect that special temperature and speed settings exist for this PLA but I've found conflicting information

Can you offer any advice to get a continuous print without blockage? My G-code is attached in case it is of interest
Attachments:
open | download - cube10.gcode (102.1 KB)
Re: Hot-end jamming
June 04, 2015 05:03PM
you need a fan on the heat sink to prevent the pla from getting hot inside the PTFE tube (if applicable) or inside the throat of the hot end.

Construction of a hot end:
Nozzle "The Hot End"
Stainless steel pipe "The warm middle"
PTFE "The Slippery Slope"
Heat sink "The Cold End"

If the warm middle gets too hot it will make the PLA swell (up to double in size) and stop moving. This causes the coiling because you have a strong extruder which is a good thing.
It the warm really gets hot, it can ruin the slippery part.
The heat sink's job is to remove heat from the stainless steel tube and keep the warm parts less hot than the hot parts.
The fan is to expedite the cooling. need the fan man.

Sorry, one more edit. I'm referring to a fan specifically for the heat sink, not necessarily for the printed item.

Edited 2 time(s). Last edit at 06/04/2015 05:04PM by thetazzbot.
Re: Hot-end jamming
June 04, 2015 05:11PM
My office doesn't seem to like Zego's website, so I can't look at the spec for your printer. Is the hot end all metal (metal cooling fins) or is the top area made out of a different material (assuming peek)?

If it is all metal, you should have a fan blowing on the cooling fans at all times (or at least when the hot end is heated) to keep the filament cool as it enters the melting pot of the hot end. Shouldn't matter with a Peek hot end, the only fan would be on print itself, and that only effects the quality of the print, it shouldn't have any impact on whether or not the hot end jams.

When you do have a jam, can you manually push the filament through the hot end while it is heated to temperature? If not, or if it is difficult or the coming out at an angle, then you have a clog in the hot end that needs to be cleaned out. Lower the temperature of the hotend 50 degrees or so before removing the filament from the hot end. Clipping the end off, stick the filament back into the hotend for a few seconds and pull out again to try to grab any remaining filament in the nozzle.

When reloading filament, make sure the PTFE tube in the hot end, if present, goes as far down into the hot end as you can get it. When over heated, the filament can expand in the gap and prevent extrusion.

Overheating the filament can cause it to expand in the PTFE tube as well, making it harder to push the filament through the hot end. One solution people seem to have great success with is applying a small amount of seasme seed oil (any cooking oil good to 240 degrees should work) to the end of their filament before threading it through their bowden tube into the hot end.

As for finding a temperature for your filament, I really liked this YouTube video from RepRap Neo. Start with 210 degrees and drop in 5 degree increments from there, eventually stepping down to 3 degree increments.
Re: Hot-end jamming
June 04, 2015 07:31PM
One more tip:

Don't preheat the hot end, or keep it on after a print finishes. What happens with a default setup is, the software will turn the fan off during the first layer, turn it on during the print, then off at the end. It should also turn off the hot end. Some people might disable this option and keep the hotend hot so they can keep printing, but you need to keep the fan running. What I found with pla (i hate pla btw) is that leaving the hotend on it makes the pla swell and clog. I get that curling all the time, hence my lack of love for pla. Might want to also check retraction speed/distance.
Re: Hot-end jamming
June 07, 2015 08:05PM
Thank you for the prompt replies and helpful advice!

> you need a fan on the heat sink to prevent the pla from getting hot inside the PTFE tube (if applicable) or inside the throat of the hot end.
> ..
> If the warm middle gets too hot it will make the PLA swell (up to double in size) and stop moving. This causes the coiling because you have a strong extruder which is a good thing.
> It the warm really gets hot, it can ruin the slippery part.
> The heat sink's job is to remove heat from the stainless steel tube and keep the warm parts less hot than the hot parts.
> The fan is to expedite the cooling. need the fan man.

That makes sense, I used a fan the second time, but it is an area fan being pointed at the printing area and it actually caused the print to warp during the job. I will look for a fan to attach to the platform and convect more directly.

> Is the hot end all metal (metal cooling fins) or is the top area made out of a different material (assuming peek)?
I'm actually having difficulty finding info on it as well. It appears to be fully aluminum, except the nozzle.

> As for finding a temperature for your filament, I really liked this YouTube video from RepRap Neo. Start with 210 degrees and drop in 5 degree increments from there, eventually stepping down to 3 degree increments.
That video would have been great to watch before I started, I'll try the steps once I get the fan installed to find the optimal temperature and extrusion speed

> When you do have a jam, can you manually push the filament through the hot end while it is heated to temperature? If not, or if it is difficult or the coming out at an angle, then you have a clog in the hot end that needs to be cleaned out.
No I can't push it through at all. I suspect you are right and it is a jam in the hot end.

> Don't preheat the hot end, or keep it on after a print finishes.
Okay, I've been doing that a lot so that is good to know

Thanks again, if I come across any new information I'll be sure to share it. I wish I heard this advice sooner
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