JHead Clogs up on long first layer w. o. fan

Hello,

Can anybody give me an advice on the jhead provided by nopheads kit? Whenever the first layer takes long the jhead heads up way to much. I print on a PEI 3mm alloy plate headed at 75 degrees and the pla is printed with 200 degrees. I cannot print the first layer with the fan running as the infill fails to stick to the surface.

Ingo

Hi,

If you follow the advice in the Build Manual you will be printing at 185C and have the fan turned off for the first layer. You should also print the first layer at 50% of the speed of the other layers.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

The problem of PLA softening at the top end of the JHead is most likely to occur when the first layer print time of an object is relatively long compared to objects which do not give rise to this problem. The solution? Speed up the first layer, switch on the part cooling fan (the version with the hole to cool the top of the JHead) or provide JHead cooling by some other method.

Of course, speeding things up or switching on the part cooling fan may well hinder the first layer sticking to the build plate and if this is the case, you may well turn to techniques such as preparing the build plate with dilute PVA as documented elsewhere on this forum.

Alan

Do you have the version of the kit that has red silicone tape on the hot end? That stops the heat from rising.

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[www.hydraraptor.blogspot.com]

Hi Chris,

yes this version features the red silicone tape and the small hole in the fan duct. I will lower the temperature for the first layer and print it at a higher layer height so the extruder can push out more plastic at a time which might introduce more cooling. I guess aluminium has a higher heat-transfer coefficient than borosilicate glass, I did not think about the problems which might arise by replacing the glas with a aluminium sheet.

The PLA I use tends to pull up the corners of the object when I lower the extruder to the suggested 185 °C. I found out by raising the temperature I am able to print very large objects without warping (I expected the opposite). Guess the 200 °C leads to more liquefaction where the PLA doesn't remember the 90° bend out of the extruder. But for the first layer it should not matter.

PS: I never found a way to contact you to say thank you for creating this kit. You keep going with a larger-than-life dedication while keeping everything open source which is unparalled. I've been through hell with my first self-sourced Mendelmax and I had countless hours of suffering while a whole year passed by without satisfactory results. I was unable to cope with the complexity of reprap and focussing on progress. When I finally gave up and looked for a non commercial plug and play alternative and finally got your kit - it was like a dream of heaven. Blueprint of a perfect manual, not a single part missing and everything well-thought-out from the beginning to the end. The printer worked after a two day assembly with outstandig results.

Ingo

Everything is fine now by just lowering the temperature slighty. I could drop a few degrees and left away the retract for the parts in question and now the printing just went fine. I've been watching the print and there where lots of retracts due to bad design of the part which messed up the filament. After three dozen retracts the filament did not retract as the transport screw was digging into the warm plastic.

Ingo

Hi,

Was this a case of slow printing speed and excessive retraction? I am curious about whether it was more due to incorrect slicing parameters.

I print a lot of my objects at 40mm/s and do not retract more than 1mm at 40mm/s. You can also specify a minimum travel distance after a retract before another may be performed which I set to 1mm.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

I print with nopheads settings, 50mm/s, first layer half speed I guess. Retration is 0.5mm at 35mm/s which creates the cleanest objects and less bloobs at the places where the z-lift happends. The minimum travel distance is 1mm. Maybe I'll try a few mm more.

I need to improve print quality some more, I'll open a new thread with a few examples.

Ingo