December 29, 2020

3D Printing - Tutorials and Videos

It has been 9 months since I have done anything with my 3D printer (my Ender 3), so I thought it would be worthwhile -- for myself if for noone else -- to follow the steps from an idea to a finished print.

OpenSCAD

What I need is very simple. A washer essentially with custom dimensions. It will be a shim for a stereomicroscope to fine tune the position of an eyepiece. The first step for me is to use the "vi" editor and create a design file "tube.scad".

I use OpenSCAD to view the design and fine tune it. I type "openscad tube.scad" to run OpenSCAD. Once I like how it looks, I type F6 to render the design, and then "File -- Export -- Export as STL" (F7 is a shortcut for this) to export the design as an STL file. I work entirely in mm. Here is the file:

Now run Cura

I simply type "cura". It prints about a million messages, then starts a GUI. This is version 4.11.0. I use "File -- Open" and navigate to /u1/Projects/3dprinting/Scad and select "tube.stl". I see my "washer" appear in the view.

I want to select more infill. There is a display on the upper right that shows the settings, but is also a menu, just click on this and drag the blue ball to 100 percent. Easy, but I need to remember to reset it for next time. A little "x" dismisses this dialog.

A button on the lower right says "Slice", so I click it.

The button changes, now predicting a 7 minute print time and offering a button to save to disk. I click this button. I get a file save dialog and save to "tube.gcode".

Take the gcode file to the printer

The printer still has the 16G micro-SD card in the slot from last time. I remove the card, put it into my card reader and type the command: 
cp tube.gcode /run/media/tom/6331-3331/
Which does the job on my linux system. I take the card back to the Ender 3 Pro. It plugs in upside down. The Ender doesn't know there is a TF card, so apparently the thing to do is cycle power -- and that does it. I select print from TF card, select tube.gcode and away it goes.

It heats the bed to 60, the extruder to 200, then I discover the filament is broken. See "printer hell" below. Once I get filament set up, it indeed heats first the bed, then the extruder, then starts printing.

First it prints a line along the far left (to get crud out of the extruder presumably). Then it prints a circle around where my washer will be. Then it gets busy printing my washer.

While it is printing, I start up Cura again and put the infill setting back to 20 percent, which I guess is the default.

Results

The inside diameter measures 29.5 mm, not 30.0, outside is 35.6, not 35.4 The all important thickness is 1.92 (not 2.0 like we asked for, but we wanted 1.90 so this is actually great). However 29.5 will not fit over a 30.0 diameter cylinder, so we need to either sand a bit or print another.

They say PLA shrinks about 2 percent, which for a 30 mm object would be 0.6, hence giving a 29.4 diameter as we see. Oddly the outside diameter did not shrink this much. It looks like good old trial and error is the only thing here. Note also that OpenSCAD approximates circles by a polygon (which I specified to have 60 points). This will change dimensions somewhat.

Printer hell

Getting filament threaded into the printer is a complex and painful process. There is a tiny hole, all but invisible because everything is black. Said hole is just beyond the stepper that feeds the filament. Using a stick to push the filament to line up with the hole can be helpful

Don't expect to be able to move the filament feed motor until you get the print head heated up. So heat up the head for PLA, then move the extruder axis until you see a worm of filament coming out of the extruder.

Have any comments? Questions? Drop me a line!

Adventures in Computing / tom@mmto.org