Slic3r and J-head observation from reprap forum

[mxk]

Sublime from the reprap forum posted this today, thought it would be useful for the folks here since so many use this combination:

After running a J-head for a while and helping many people get started (here and in our local R.U.G.) Myself and others have come to a realization that the prints turn out far better when "fudging" the nozzle diameter in Slic3r. I decided to look into this further and it seems Slic3r expects a nozzle to print far wider than is possible (at least with a J-head). When you slice an object with Slic3r set to use a 0.5 nozzle and 0.25 layer it generates gcode with the expectation that a single wall will turn out 0.7mm wide but the flow capacity of the J-head does not seem to allow that much flow.

When doing a free air extrusion with a 0.5mm nozzle I get 0.55 -0.6mm diameter
When doing a free air extrusion with a 0.35mm nozzle I get 0.4 - 0.45mm diameter

I never noticed this on my homemade hotends and think this is because I could never get a perfect hole so I was actually using a smaller setting than the nozzle anyway.

My findings are:

0.5mm J-head @ 0.25 layer needs to be set at 0.4mm which gives a path of 0.53mm
0.35mm J-head @ 0.2 layers needs to be set at 0.3 which gives a path of 0.37mm


Problems this has solved:

Infill not touching the perimeters.
Infill not touching the infill next to it.
Perimeters not touching each other.
Blobs from excessive pressure due to trying to extrude more plastic than the hotend can flow.
Extruder skipping steps.

I know you can set the width over thickness manually in the advanced tab but find this annoying because you need to re-calculate it every time you change layer heights. By fudging the diameter of the nozzle you can still just change the layer and let Slic3r do the rest.

[Enraged]

thanks, I have a 0.35mm J head, I'll update my settings.