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Kossel delta suddenly over temp PLA conditions occur

Posted by dlc60 
Kossel delta suddenly over temp PLA conditions occur
May 03, 2017 11:10AM
This is the second of my Kossel delta printer questions.
My configuration:
Folger Tech Kossel 2020 kit build running Marlin firmware from the factory (C)2011.
My slicer/printer software is Simplify 3D running on a Win 7 computer.

Until yesterday, my delta printer was "dialed in" and printing whatever I threw at it. My bed is flat, auto-leveling was working like a charm. I have a part fan that is off for the first layer and set to 50% at layer 4. My bed is at 60 C and my hot end is at 210 C for the first layer and backs off to 200 C for all layers after that. I work in PLA.
Then, suddenly it developed problems.
The first problem was my endstops suddenly changed by 0.3mm. After I "fixed" that problem and started printing, this started happening.

Models printed great, dragons, space ships, calibration cubes, project enclosure boxes, everything worked fine and I was using about 75-80% of the bed to print.
Now, I cannot print anything but models with a large contact patch to height ratio. Boxes: fine, parts with multiple contact patches on the bed will have sections knocked over and dragged around.
Even flat models now are festooned with "cobwebs". Gunk gathers and creates "zits" in places and more scars than usual on surfaces. When I try to print models that have several contact spots on the bed, the plastic may warp on a layer and when the print head comes along may hit it and knock it off. Also, it may be dragged around by drools from the hot end. I now see dark sections that look like the plastic got burned while coming out. I have attached an example "print".

I have not changed any of my print settings. I use the same temperatures and switchover points as I did before. These issues clearly point to over-heated plastic. But why now? Do thermistors go bad in such a way that they report incorrectly and the print head is actually much hotter than being reported? Has anyone ever seen this kind of behavior?

I am going to continue working on this, and will report results, but if anyone has any ideas I would surely appreciate reading them.

open | download - IMG_2482.JPG (446 KB)
Re: Kossel delta suddenly over temp PLA conditions occur
May 03, 2017 11:41PM
perhaps something mechanical, your extruder gear is slipping?

Thermistors do go bad, but usually they just fail completely. Have you monitored the temps on the display are they constant or do they move around?

You could do the PID tuning, this will keep the temp more accurately closer to the temp that you have set in the slicer.

If using marlin, use M303 see reprap wiki for help, but these will run PID tuning, then you set the values in the config file.
Re: Kossel delta suddenly over temp PLA conditions occur
May 04, 2017 01:25AM
The whole problem was caused by my wire harness pulling on the heater block which caused it to unscrew a few degrees. This caused PLA to leak out the top of the heater block, burn and dribble down on the print job.

How is that for weird? It is definitely a mechanical design flaw when there is no way to lock the heater block to the filament feeder tube. I have more carefully re-routed my wiring harness to hopefully avoid this in the future. AND I will be watching for it now!

thanks all,
Re: Kossel delta suddenly over temp PLA conditions occur
May 04, 2017 02:41AM
Its best to tighten the headlock and nozzle at high temps, of if you still find that its loose (enough for your issue to happen) try a high temp lock-tight or plumbers tape (most are PTFE)
Re: Kossel delta suddenly over temp PLA conditions occur
May 04, 2017 11:16AM
I will add that to my notes and best practices "tips to future self".

Every new hurdle leads to more knowledge, right?

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