Extruder keeps jamming!

Help!

I have tried a number of extruder designs and I keep running into the same problem in that after I have produced about 300mm of thread the extruder jams and doesn't extrude any more.

Current attempt is with the Machined Extruder Parts Kit by reifsnyderb where I am using the Heater Barrel, PTFE Thermal Barrier and Nozzle Tip from his kit.

[forums.reprap.org]

For heat I am using my power resistor pack.

[exmrclean.blogspot.com]

I get everything wired up and either push the fiber as far in as it will go before I turn on the heat or I wait for it come up to 240c and then start pushing.

Under either method it extrudes for a bit and then jams.

I am using a 100K Thermistor with a Sanguino and the Temperature Sensor Kit with the Thermistor attached to the nozzle.

My ABS is a 5lb roll from the store that is slightly cream colored.

The temperature holds steady at 240c and I am using the following table:

// Thermistor lookup table for RepRap Temperature Sensor Boards (http://make.rrrf.org/ts)
// Made with createTemperatureLookup.py (http://svn.reprap.org/trunk/reprap/firmware/Arduino/utilities/createTemperatureLookup.py)
// ./createTemperatureLookup.py --r0=100000 --t0=25 --r1=0 --r2=4700 --beta=4066 --max-adc=1023
// r0: 100000
// t0: 25
// r1: 0
// r2: 4700
// beta: 4066
// max adc: 1023
#define NUMTEMPS 20
short temptable[NUMTEMPS][2] = {
{1, 841},
{54, 255},
{107, 209},
{160, 184},
{213, 166},
{266, 153},
{319, 142},
{372, 132},
{425, 124},
{478, 116},
{531, 108},
{584, 101},
{637, 93},
{690, 86},
{743, 78},
{796, 70},
{849, 61},
{902, 50},
{955, 34},
{1008, 3}
};

Edited 2 time(s). Last edit at 03/04/2009 09:19PM by freds.

That's weird.

BTW, I bought and am trying to use several of the conversion products from Tangible Software that you recommended.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

freds,

One possibility is that you simply don't have enough drive. It is much easier to push cold filament into an empty barrel than it is once the molten plug has formed. As the insulator warms the transition zone becomes longer and more force is required.

You probably need more spring tension.

As you know I have been doing a lot of work on this and will be blogging some more results in the next couple of days.

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[www.hydraraptor.blogspot.com]

Hi Nophead

The forum was down today and your post went astray.

I can see it just above yours.

Quote

freds,

One possibility is that you simply don't have enough drive. It is much easier to push cold filament into an empty barrel than it is once the molten plug has formed. As the insulator warms the transition zone becomes longer and more force is required.

You probably need more spring tension.

As you know I have been doing a lot of work on this and will be blogging some more results in the next couple of days.

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[www.hydraraptor.blogspot.com]

Hmmm it now seems to have corrected this thread.

I have a variation of demented's design for the feeder and it will grind away the fiber when it stalls.

I am wondering if the thermistor is way off in the upper heat range?

When I take it apart and clean it up; the plastic is a mixture of translucent, yellow and much much harder then the virgin fiber in a crush test with needle nose pliers.

Yes it is always the case that a stall results in grinding away but it can be due to the thread not being sharp enough to bite in, or not enough force on the roller to get it to bite to the full depth.

Having said that your description of the filament is not something I recognise. In my experiance natural ABS is cream coloured and goes it bit yellow on the outside when exposed to light. When it gets too hot > 280C if goes brown and hard. I have never seen it go translucent.

When it is way too hot you get lots of smoke and popping sounds. It can produce a hard solid that blocks the nozzle.

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[www.hydraraptor.blogspot.com]

ok I have gotten some sort of brown or tan thread out at times. Whats the lowest tempature I should try to extrude at, should I do one more cleaning and use acetone to get it spotless?



Back to fource on the feeder mechanism, what would be a good way to test it? I.E. It must lift 8lb's or one gallon container of water, etc?

Yes the brown stuff looks like it got too hot, assuming there was not contamination (oil, grease, etc). The top picture does not look like it got too hot.

ABS melts about 110 IIRC and can be extruded easily anywhere between 180 and 250. At 260 it starts to denature. Any plastic left exposed to the air at extrusion temperatures will go black eventually, for example bits stuck to the outside of the nozzle. The plastic inside the nozzle, seems to withstand the temperature for much longer. Air is excluded and volatile products cannot escape.

I use acetone to remove plastic from threads, etc. It is not necessary to remove it otherwise, unless it has gone hard due to being burnt. In that case I find it brittle and powdery, so easy to remove with a probe. No need to get is spotless but you do have to get rid of any hard burnt bits that wont fit through the nozzle.

My "three times better" extruder needs about 2.5Kg to extrude ABS at 240C through a 0.5mm nozzle at 3.5mm^3/s. Other designs are worse (typically by 3!) and some will not extrude no matter how hard I push. A big clue is when you pull the filament back out from the top while the heater is on. The molten end comes away and stays in the heater. The bit that comes out has a section that has softened and expanded to fill the inlet bore and the rest is untouched filament. The expanded section is the plug that causes all the problems. It should only be a few mm long. If it is say 20mm long it will be almost impossible to shift.

I haven't measured a drive mechanism yet but for ABS I think it would need at least 5kg pull to be reliable.

Edited 1 time(s). Last edit at 03/06/2009 03:09PM by nophead.

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[www.hydraraptor.blogspot.com]

Ok I will try extruding at a reading of 200c rather then 240c the next time. That should reduce the size of the plug zone.

The top piece is definately more brittle and hard then the virgin fiber, so I think it was also being cooked a bit.