[RESOLVED] - Extruder flow problem

Hello :-)

I am having a problem since ever. My extruder do not extrudes at constant flow.

It extrudes like for 15 seconds and after during 4 seconds it stops, like if is jammed, again extrudes for 15 seconds and another 4 seconds stops, and continues like this.

I can clearly see the motor running at constant speed and when extruding stops motor continues to run but plastic filament don't go further.

If I lower the temperature, the time it stops extruding is higher...

Yesterday I started to use a new stepper motor of 0.43Nm and a pololu controller. Before I were using a 14V 0.22Nm from Makerbot store and extruder board to control it. I thought the problem were with my stepper motor but now I see that not.

My first idea were that plastic filament didn't have enough time to get hot inside brass barrel and so I disassembled the extruder and put more area where heater is placed, to try give more place for plastic filament get hot. The problem remains...

Can some one help me? any ideas?

Thanks in advance.

Edited 1 time(s). Last edit at 02/02/2010 06:51PM by casainho.

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... sounds like 'thermal oszillation' because of lack of energy ... but trapped airbubbles can cause a similar behaviour.

I think you should try first with more NiCr-windings or more heatinducing area and second with better thermal isolation of the hot tip ...

Viktor

VDX Wrote:
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> ... sounds like 'thermal oszillation' because of
> lack of energy ... but trapped airbubbles can
> cause a similar behaviour.

I am setup temperature so I don't get airbubbles (airbubbles means to much hot, I guess).

When it jams and starts again, then there are some airbubbles, but I guess that is because plastic filament gets to hot if it not moves.


> I think you should try first with more
> NiCr-windings or more heatinducing area and second
> with better thermal isolation of the hot tip ...

I am using temperature isolation but not on the tip (end of brass barrel?). The tip is not really insulated...

Thanks :-)

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What heater / thermistor arrangement do you have? It certainly looks like the temperature is swinging around.

Perhaps there is poor conduction between the heater and nozzle, or not enough power. When you extrude at 3mm^3/s IIRC it needs about 2W more to heat the plastic, so if your heater does not have 2W to spare then the temperature will fall as you extrude until it jams. It will then be able to warm up again.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> What heater / thermistor arrangement do you have?
> It certainly looks like the temperature is
> swinging around.
>
> Perhaps there is poor conduction between the
> heater and nozzle, or not enough power. When you
> extrude at 3mm^3/s IIRC it needs about 2W more to
> heat the plastic, so if your heater does not have
> 2W to spare then the temperature will fall as you
> extrude until it jams. It will then be able to
> warm up again.

I had assembled and disassembled it a few times today.

Here a picture:


Since I couldn't find insulated nichrome wire on local shops, I just did found the nichrome and an insulator which is a bit large... you can see it on that picture, under kapton tape. I am insulating the thermistor and nichrome wire with that insulator.

I see on EMC2 GUI the heater temperature changing only +-1 ºC, and very quick the action when temperature PV is less than temperature SV.

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Are you sure the thermistor is reading the actual temperature of the nozzle and is not seeing the heat from the nichrome directly?

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> Are you sure the thermistor is reading the actual
> temperature of the nozzle and is not seeing the
> heat from the nichrome directly?

You are right. It were last time I assembled the extruder.

I took of that big washer to see if the problem was there. I had assembled and disassembly many times the extruder on last hours. Luckly I had a lot of nichrome wire, insulation for it and PFTE. For the first time in my life I used a pice to make threads (M6 on PTFE) :-)

The problem remains :-( -- I took a picture of actual setup of my extruder e recorded a video showing the problem. Temperature were at 230ºC and swinging at abour +-5ºC.

Picture:


Video:


Edited 4 time(s). Last edit at 02/02/2010 01:39PM by casainho.

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Is that noise a dog or does your extruder bark as well ?

130C is far too low for ABS so I expect it gets too viscous with a 5C swing. I use 220C on a hot bed and 240C otherwise. 5C would not make much difference at those temperatures.

Is the light I can see an LED or is it the nichrome glowing?

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> Is that noise a dog or does your extruder bark as
> well ?

Eheh, it's my dog :-)


> 130C is far too low for ABS so I expect it gets
> too viscous with a 5C swing. I use 220C on a hot
> bed and 240C otherwise. 5C would not make much
> difference at those temperatures.

Sorry, my mistake. It s at 230ºC.


> Is the light I can see an LED or is it the
> nichrome glowing?

Nichrome glowing.

Another try
I just went to put nichrome wire on all brass barrel until PTFE. I get the same problem, not any better.

Picture:


Even more tries

On IRC channel, Kulitorum told me to leave out the fiberglass insulation on nichrome wire that I am using, and instead use kapton tape. I did but I get the same problem...

Now I did registered a video showing motor shaft, Tonokip asked for this video:


RESOLVED!!!!

On IRC they told me after seing this video that the teeth part is off-center... and that's right because I drilled it for 5mm.

Thank you all :-)

Today, 03.02.2010, I decided to go shop and buy brass bar of 10mm diameter. My idea was to make try make a gear, cutting the bar, drill a hole of 5mm at center and grind to make tooths. I was not successful because my bits were cheap and are shit :-(

Lucky on shop I also bought a coper tube (to try later make and extruder for 6mm plastic filament that I can buy on local shops). Since I had with me a pulley I bought from Makerbot store for the DC motor, I decided to try use it and also use the coper to fill the gap between 5mm stepper motor shaft and 6mm pulley. It works :-)

Here I picture of my tools and my work of today:


Edited 4 time(s). Last edit at 02/03/2010 09:54AM by casainho.

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

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