Something with woods and trees (I don't get it)

[cubic 0]

Hi All,

Although I am the first owner of my UMO, I am no way an expert. I have been making things, but I am not happy with the results. In hindsight printing always has been troublesome. Let's say mixed results. But more and more I am using the printer in projects and I have seen much better print quality than what I get. Often I have vertical outer walls not connected, or the top layer not showing a closed surface. So a simple print quality topic? No!

Recently I printed 3 clamps and Cura told me they should weigh 59 grams. I doubted that and so put the clamps on the scales. It turned out to be only 29 grams. And I  should tell you that I am printing at 110% material and 210°C. So the 29 grams would have been only 26 grams at 100%. So close to 50%. Oh, the feeder is wrong? Maybe the stepper is doing half steps?

I took the Bowden cable fron the head , cut the filament flush and had it extrude 100mm. And it was exactly 100mm.  The gear moves about 4.25 revolution. All good.

However, when I re-mount the Bowden cable, preheat the thing, and mark the filament 100mm before the feeder and then extrude 100mm only 60mm went in.

I have listened closely but I do not hear steps being lost. So it is slip then? Maybe a bit more force in the feeder? No! it does not make any difference.

Knurled bolt blunt? No!

Maybe dirt in the nozzle? Well it is obviously not new but I took it out, got the material out and could look through. Used dentist  tools and had a good look inside the nozzle; it looks like a new one. When taking the nozzle out I saw that the nozzle was not really against the aluminium block, so no good thermal contact. I remounted it so that the nozzle now is firmly in and against the Alu block. After all this about 75mm go into the feeder when I ask for 100mm.

Next I elevated the temperature because I saw with a thermal camera that the temperature of the nozzle is only 185°C. I ended up setting the temperature  at 240°C. And that for PLA. It should come out brown, what ever colour you put in, isn't it?

 

Is my thermocouple gone?

 

But still at 240°C.... it extrudes only 82mm when I ask for 100m.

I am at the end of ideas. Please help.

 

Regards,  Cube.

 

 

Edited April 30, 2020 by cubic

[SandervG 1,521]

Hi @cubic, thank you for your message. In addition to your thorough description, could you also post some pictures of your prints? That will probably also be a valuable tool to assess what might be wrong. Thanks! 

[cubic 0]

Hi Sander, 

Thanks for the invitation, although my first reaction was "the weight is wrong, how to photograph that?". But anyway it may be a good idea that more experienced people give their view on this. Please find two photo's attached. The left one is what started this search, so the prints before any  of the actions described above. The right one is what comes out at 240°C and at 110% material in Cura. I am not unhappy with that, but it is still the weight is too low, Cura says 19 grams and it is 16 to 17 grams. Close but no cigar.

 

Photo top view:

What I think I see in the top photo; at the left part you recognise lose outer walls (right of the right leg and at the bottom at the left. And I see the top not being filled, where it looks like things go especially wrong when the printer is in a hurry. To me it looks like the temperature is getting lost and less and less material is provided.

At the right part all looks a lot better, maybe even over extruded in the left leg but remember this is 100% material. Maybe even I should not complain about this. But wait, lets look at the side:

 

Photo side view:

The left part shows signs of under extrusion. It warps. And the top half of the wall looks good, but remember it is connected to nothing inside. It is a 0,3mm free standing wall. If you wanted this, you'd not be able to design and slice it. The "dashed layer" about 1/3 up is the same all around the object, you see this in all walls.

The right part has been damaged a bit when removing the brim, sorry, just ignore. Still it warps a bit. I'll save up some money and get me a heated building plate. But the "slits" worry me a bit. Never had that before. Maybe it has to do with the temperature. At this point I am not all to worried about that.

 

What worries me most is that with the 240°C setting the weight is too low. And only 82mm is extruded when I ask for 100mm. Knowing that it does extrude 100mm with the Bowden cable out of the printhead.

 

Thank you all for your time, regards, Cube.

[SandervG 1,521]

Hello, thank you for your message. 

It is not necessarily the weight that I suggest to capture in a camera, but it is indeed under extrusion and sometimes the way that it manifests can be a lead to the reason. Could you also share a picture of your print head, and the way the heater cartridge and thermocouple sit in your aluminum block? If not inserted fully / correctly, this can also lead to heat loss or incorrect measurements. 

 

The slit 1/3rd in your print could be because of dirt on your threaded axis on the back. Have you ever cleaned it? If you clean it, make sure to reapply the grease you have received together with your Ultimaker Original. 

[cubic 0]

Hi Sander,

 

It took some time; life got in the way.

This photo, I think, shows that the heating cartridge and the sensor are in okay: 

The side view shows a more general impression.  I noticed that the front (left in the picture) screw is not tight, but there is no way I can tighten it more than this. Looks like the ring of the Peek bush is thicker than the space provided. The "blood stain" on the Alu block allows for the thermal camera to be used.  Recently I disassembled the nozzle from the Alu block and found that is was no contact between the Alu and nozzle in the surfaces around the thread. Now there is as you can see.

And from the rear the fan duct  is in the way but I hope this shows what you wanted to see.

I've no clue what you hoped to see, but okay. 

Maybe I should inform that the temperature controller seems to work alright in that the setpoint and process temperature are always close together during printing. But I have the feeling that if the controller measures, say, 240°C, the actual temperature is something like 210°C. Do thermocouples wear out?

 

regards,  Cubic

 

 

 

 

Edited April 30, 2020 by cubic

[Torgeir 243]

Hi Cubic,

 

You have certenly tried many thing in order to correct your problem.

The problem with the thermocouple is of a special character.

All this is because of the short distance between the “hot junction *)” and the “cold junction *)” in your, -well, the UMO design.

Let me explain. Using a thermocouple to measure absolute temperature in a setup, ask for a special converter. This is true because a thermocouple is reading a temperature between two point *).

This converter is mounted on the top of the UMO extruder. This converter measure the absolute temperature at the green terminal block where the thermocouple (red and yellow) wires is connected. This point is named “cold junction” point. Right here, it is really important to have good thermal and electrical contact here. Say you have a proper electrical contact here, you’ll read a proper voltage here, but temperature is still showing to high.

As the temperature (that is transported via the wires from the close by extruder) is not evenly distributed to the “cold junction” point, the temperature read at this point will be wrong and will lead to “calculation error” of extruder absolute temperature. As the sensed temperature is lower than is should be the calculated temperature will show higher than the actual temperature.

 

So I do not think you have an error in your thermocouple, most likely this is just because of little clamping effect at your “cold junction” terminal. Sure, it could be the compensator, but not likely.

 

Just a small note, make a black mark on the extruder to measure with an IR detector, this is what we use in lab for calibrating measurment (ref black body).

 

Ok good luck.

 

Thanks

 

Torgeir

 

 

 

[cubic 0]

Both Torgeir and Sander thank you for the input. It really helps. 

 

It much looks like Sander's suggestion regarding the faulty layer one third up was correct. I added some weight to the printing table and the problem was gone. Thank you.

 

And Tongeir, thank you for explaining the thermocouple operation. I did know that but good for completeness. For my work I use thermosensors (melting plastics 😉 ) on an industrial scale. When I have to choose, I will never use a thermocouple. I simply cannot trust millivolt signals in high power installations (although I know the majority uses them). I rather use Pt-100s even when I know that Nasa engineered them out of their spacecrafts for reliability reasons.

Today, finally, I got the possibility to measure the temperature with a proper Pt-100. When set to 250°C and the controller indicating 250°C, the side of the Alu block measured 210.2°C. I made several attempts and have been using thermal compound between the alu block and the sensor but 210.2 was the max. Very likely the actual temperature may be somewhat higher but it certainly will not be 250.

And I can see that a too low temperature causes the problem I experienced; too little flow.

 

Reconnecting the thermocouple wires has made no difference. They were firmly screwed down and are again now.

 

So the conclusion is that the actual temperature is much lower than indicated. In my opinion it is either the thermocouple or the compensator that is in error. How to find out? Or solve this differently and switch to Pt-100? (easier to check)

 

Thanks for any comments.

Cubic