Friday, July 31, 2015

Experimenting with PLA

I'm experimenting with PLA filament on my Printrbot Classic 3D printer. Slicing with Slic3r 1.2.9. Printing with Octoprint.

Filament is not sticking to bed. The model is large but small surface area - basically a third of the perimeter of a circle with radius 100 mm, perimeter is 2 mm wide. I also have a new fan assembly which is not perfect.

Bed measured temp is around 71. Hotend temp set to 215.

Set first layer speed changed from 25% to 15 mm/s. Retry.

I think head was too far from bed. Changed G92 Z-1.6 to G92 Z-1.5 in printer init script.

filament is coming out of printhead unevenly - in globs.

Removing fan assembly. Reducing printhead temp to 210 to try to reduce uneven PLA flow. Changed G92 Z-1.5 to G92 Z-1.45. Reducing max print speed from 120 to 80 mm/s.

First layer still not sticking properly. Still uneven flow.

Lower printhead even more, to Z-1.35. Globbing could be because not sticking properly?

Still not good. Unsure if the G92 Z stuff is having an effect. Perhaps I should go out and buy blue painters' tape or hair spray.

Changed to G92 Z-1.1. Still looks the same.

Now tried adjusting Z-stop screw instead of G92. Removing G92 command. Retry.

That seems to have done it!

Continued experiments:

Added a spoke to the model. Changing first layer speed from 15 to 20 mm/s. Changing max speed from 80 to 100. Calculate volumetric speed equivalent of 100 mm/s: cylinder 2.85 mm diameter x 100 mm volume = 638 mm^3 / s. Test with 638. Increasing layer height to 0.4 mm.

Worked fairly well. Print time 44 minutes. Extruder stepper was losing steps when printing the smaller top part. That part also turned out poorly, probably no fan caused it not to have time too cool down. For the next one, try a minimum layer time (30 second layers were good, 5 second layers were bad), slower volumetric speed, try even higher layers (0.5 mm).

Changed minimum layer time to from 5 to 30 seconds, max volumetric speed to 500, first layer speed to 20, layer height to 0.5, default extrusion width to auto. Print time will now be about 90 layers * 30 seconds = 45 minutes.

The extruder stepper is still losing steps. I don't understand why. Stepper motor weak because it is hot? trying decreasing pressure holding filament against knurled bolt in extruder. I think reducing this pressure fixed the problem.

Note to self: next time, thread the filament from the spool, through the 'b' in the pb (PrinterBot) logo on the Power Tower, so that the filament is not pulled sideways off the spool.

Worked well. Slower layer times appear to be an alternative to having a fan.

Continued experiments 2015-08-02

Made a fan attachment model in FreeCAD (fairly difficult design for me). Printing with 30% infill. Increasing layer height from 0.5 to 0.6 mm, max print speed from 100 to 120, max volumetric speed to 550, first layer speed from 20 to 25 mm/s.

Extruder skipped. Raised extruder temp to 215. Head was too far from printbed. Needed to back off on Z-screw 1.5 turns.

Got a printout. It was pretty rough, stringy. Some parts of layers didn't attach properly. Dimensions were not very accurate. Maybe 0.5 layer is just too rough. Trying to print it at 0.3 mm. Max print speed at 100, max volumetric speed 500, first layer speed to 30 mm/s.

Printout turned out fairly well. A bit of unevenness, but OK for a structural part that doesn't have to be pretty.

Changing seam position to nearest, decreasing filament temperature from 215 to 213. Increasing first layer speed to 40 mm/s, decreasing diameter from 2.85 to 2.83 to decrease extrusion. Decreasing bed temp from 42 to 40 (Note that my temp sensor is wacky, so this is not the actual temperature), don't combine infill (so little infill anyway in this model). Sent to printer, will print tomorrow.

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