Printer nozzle overheating?  

Re: Printer nozzle overheating?

Hi Wilfred

254 degrees is way too hot for ABS on the 1.75mm printer.

You need a maximum of 230 degrees when using Prusa-supplied ABS. I find that 215 to 220 works well.

The 1.75mm printer is limited to this maximum within firmware. Temperatures in excess of 245 degrees can damage the Lite6 extruder as the PTFE tubing will start to melt.

Peter

Re: Printer nozzle overheating?

I did try to print at lower temperatures but then the layers won't stick. I even print without the cooling fan aimed at the nozzle..

Perhaps something els is not entirely right: the temperature of the printer and heat bed is about 30 degrees C when idle but the room temperature is somewhere between 15 and 20 degrees C so the printer measures at least 10 degrees too high.

Re: Printer nozzle overheating?

Wilfred

I believe that the thermistors should measure 100 kOhms at 20 degrees. Can you measure this at ambient temperature and let me know both the room temperature and resistances?

I don't often print with ABS, but I believe that one of the problems with that material is delamination, especially with taller models. I have read that increasing the layer height/width can help with this.

Peter

EDIT: When printing with ABS, you do need a very hot bed (larger model = hotter) and all drafts need to be excluded from the print area - this is why many printers are "boxed".

Re: Printer nozzle overheating?

After leaving the printer and thermometer alone for over an hour, I started measuring.

Room temperature 19.4 C
Printer nozzle: 28 C
Printer heat bed: 28 C

I removed the connectors from the RAMBo when measuring

Resistance of nozzle sensor: 125.8 k
red/black cable with yellow/green sleeve

Resistance of heatbed sensor: 125,8 k
2 white wires

The resistances of the sensors dont seem to be too far off?

Re: Printer nozzle overheating?

Wilfred

I was incorrect; the 100K reading is at 25 degrees, with the reading at 20 degrees being 125,470, so it would seem that yours are as they should be.

It does not explain why the displayed temperature is too high - resistance at 28 degrees should be around 90K. Note the above resistance are according to the heated bed thermistor table.

Do you have standard firmware installed and if so, what version?

Peter

EDIT: I presume that you have not changed the thermistors?

Re: Printer nozzle overheating?

I run your latest original firmware:

FW Version: 2.2.1 (December 18, 2015)
FW_RAMBO_MINI_1_3_175_v2_2_1.zip

Re: Printer nozzle overheating?

Wilfred

It's not my firmware. I am just a user, trying to help...

I will see if I can find an answer. Leave it with me.

Peter

Re: Printer nozzle overheating?

Sorry, you're right, I assumed you were an employee of Prusa Research.

However, thank you for your help so far.

Re: Printer nozzle overheating?

That's OK no problems; look at my signature and location...

Just trying to get an answer for you.

FWIW, my idle temps are within 1 degree of ambient.

Peter

Re: Printer nozzle overheating?

Can you post a detailed picture of the nozzle, so we can see the thermistor and the wires coming out to the wire harness?

Re: Printer nozzle overheating?

Re: Printer nozzle overheating?

Another print failed (Tower of Pi). This time I printed at a slightly lower temperature: 250 C. Again the printer stopped with the error "extruder switched off. maxtemp triggered"

Now I'm printing the same Tower of Pi, now at 240 C

It makes no sense though since I managed to print many, many, many times and many, many, many hours at 254 C.

Guess i'll need to look for a short in the circuit. Perhaps that causes the error.

[s]My other 'problem' with the 29 C idle temperature isn't solved that way but that 'problem' at least lets me print, it may explain why I need to print at higher temperatures. Example:[/s]

Marvin printed in PET at different temperatures:

Advised temperature results in a very bad print.

But first I need to find the cause of the extruder error. Then I need to find the cause of the 29 C instead of 20 C idle temperatures. (I think the last isn't caused by the thermal resistors since they both show the same (wrong) tempreature so the cause probably is somewhere else like firmware, power supply or......)

[edit]

Today I noticed some strange behaviour:

Notice the temperature drop and spike with the extruder and the temperature drop at the heatbed

[edit2]

Never mind the wrong temperature when idle. The troubleshooting video mentions this: when the temperature is about 30 degrees C when idle, it's okee (0:30 of the video). I didn't mind it even though I didn't know it was okee until the overheating occurred, I thought the problem might be connected but apparently it itsn't.

[edit3]

Here I'm printing Tower of Pi at 230 degrees. Cooling is off. I don't know if it happened at the same time but the layers shifted about 4mm along the Y-axis This only happened to me twice when I had the printing speed way too high. The current printing speed never gave a problem (printing 100 mm/s max, travelspeed 130 mm/s max).

Re: Printer nozzle overheating?

Hi Wilfred

Those graphs do seem strange.

They look very similar to my tests with higher temperatures when I turned on the print fan, but I don't think your fans is turning on?

Is the printer in a drafty location?

What mains voltage are you running from? Is it stable? Do you have a UPS powering the printer?

Can you measure the resistance of the heater coil for me. It should be slightly over 5 Ohms.

There is an algorithm within the printer used to keep the temperatures constant. It may be that your extruder heater is too powerful and is reacting too quickly, hence an over-adjustment occurs generating a MAXTEMP error.

Not convinced that your temps reading 29 degrees when the room temp is only 19 is OK. Your thermistors measure the correct values for the 19 degrees and that is the temperature I would expect to be displayed.

Do you have any way to check the hot temperature? I use an IR thermometer designed for R/C cars. When I point towards the heater block, it will read within 5 degrees of the display (usually lower due to the placement of the thermistor).

The other thing you could do (once you know the hot temperature) is to compile the firmware with an increased upper temperature limit.

Peter