Some issues with mk2  

Re: Some issues with mk2

Sorry - if you did I missed that.

I'm not sure why you are flying in the face of all the examples on here that show turning the fan down solves the issue, or against the advice given directly by Prusa though. A dodgey connection would be dodgey regardless of the fan speed.....

Perhaps you haven't got the fan shroud fitted properly ? you can block half the outlet if it isn't located inside the shroud fully.

Either way, my advice would be that if you have thermal runaway issues after layer one and your fan is on 100% - turn it down. If you still have issues then you might have a connection/thermistor issue.

Browsing through the last few pages and finding a few threads of thermal runaway problems I can only find your own thread where you confirmed it worked for you. I am genuienly curious, please point me to some other confirms.

I am not trying to be in anyones face. I just apprectiate finding the root cause of problems.

Re: Some issues with mk2

Turning down the part fan only ameliorates the symptom--it doesn't solve the problem. 100% fan seems to be required in all of my bridging, so turning it down causes other problems downstream.

Some people like to point to the part geometry, suggesting that the gaps in infill might reflect air up to the nozzle and cool. In the thermal runaway on 3.0.6 thread, I posted a bit of gcode that will guarantee thermal runaway at temps of 210C after having printed 1 layer and starting on the second flat layer. While geometry could exacerbate, it doesn't cause.

Others like to point at the old bulb vs. new cartridge thermistors. I have the old, and many are experiencing it with the new.

With the newer thermistor, an oft-pointed to problem is the connector. This certainly is a cause in many situations, and removing the connector is certainly warranted for highly variable reported temps. However,I have the older connector and experienced guaranteed thermal runaway.

PJR, in the same thread as above, detailed a process to test the heater cartridge as a possibility. Mine was in spec, as I suspect are many others. It doesn't appear to be the heater cartridge.

The long and short of it is that nobody knows what exactly is causing the thermal runaways resulting from air blowing on the heater block.

What are the solutions?

That's it. Until Prusa can figure out what else might be going on.

Re: Some issues with mk2

Curtis

You have that spot on. The problem is that the issue is only present on some printers and not others and there so far appears to be no communality although there must be somewhere.

Whilst I have never had this issue since the early days of the Mk1 where I redesigned the fan nozzle and rectified the problem on that printer, plenty of others have consistently reported it as an issue for them.

I have never experienced this issue with the Mk2; I did upgrade to the later V6 with a sock to help reduce printing costs. With the sock and a 27Ohm heater cartridge, my Mk2 can maintain 260 degrees with 100% fan without any difficulty with the sock fitted - I have not tested to see just how high I can push the temperature beyond 260 degrees.

Other than that suggested elsewhere, I really do not know of a cure for this issue and likewise for PR. All "cures" so far appear to be simply work-arounds which may or may not work for some.

This problem will only be resolved when someone at PR can have a look at one or more printer(s) which constantly exhibit this behaviour and identify precisely what is happening.

Peter

Re: Some issues with mk2

The simple change that fixed the thermal runaway issue for me was to turn the MIN fan speed down to 40 (from 85). After that I had perfectly flat line temperature graphs...until my part fan broke. 🙁

The idea was that the part fan really didn't need to be at 85% all the time, only when doing bridging and for smaller layers. Making this simple change has not seemed to affect quality at all. I haven't been doing parts with a lot of overhangs, so that would be something to watch for.

I do think it is possible that when I built the kit, I tightened the fan nozzle more than I needed to, slightly changing the direction of air flow. I remember something sounded like it snapped when I tightened the screw, but I didn't see anything broken. Maybe this is why people are seeing different results under the same circumstances, but that is just a guess. When I install my new fan I'll try to be careful with that step and see if that changes performance. Even if that's not it, variations in the printed parts could also cause a slight airflow change I suppose.

BTW my results are with the older-style thermistor. I recently received the block & sock upgrade so I'll be trying that soon, too.

Re: Some issues with mk2

Yeah, but turning down the fan is not a fix and should not be necessary.

There should be no problem to print at 200 degrees with the fan at 100%. 200 degrees is all you need for the majority of PLA prints (personally I run @ 205 and turn up the speeds a tad).

Before I upgraded to the V6V2 I didn't have a problem and still don't. I did have to alter the PID values for the hot end upgrade, but that is all.

Peter

Re: Some issues with mk2

Yeah, but turning down the fan is not a fix and should not be necessary.

There should be no problem to print at 200 degrees with the fan at 100%.

I do wonder how the "200 degrees at 100% fan" rating is tested. For me, it really depended on the object I was printing. The rating can't possibly be tested in all conditions, but it should at least be in a condition that would be likely to show evidence of electrical or heater problems.

As I said before, I turned the "minimum" fan speed down to 40%, but the maximum is still 100%. So when Slic3r decides it doesn't need the fan much, it runs it at 40% power. Depending on the situation, it may increase the power. For small layers and bridging, it runs the fan at 100%. Even then, I don't see the temperature fluctuation any more.

Anyway, after my experience, I don't feel like my printer has a problem, and I've been getting great quality prints, but I am open to the idea that I'm missing something. 🙂

Besides the fact that my print fan is currently broken. 🙁

Re: Some issues with mk2

I have a 'generic' Prusa i3, also equiped with an E3D hotend and a blower fan with a nozzle to channel the airflow. Also that hotend is not able to keep up the temperature when the fan blows at 100% (actually it's so efficient I can't set it to more than 50%), so I'm not surprised to see the same happening on the Mk2.