MakerBot CupCake’s Triumphant Return, Part 2: Skeinforge Slices; CupCake Prints

With the CupCake printing successfully again, the next step was slicing so that I could print new things instead of only reprinting G-code that I’d saved in 2012.

As noted before, I hadn’t figured out how to get Skeinforge to run on a current computer, after losing my previous Skeinforge installation to the crashes of both my personal desktop and laptop computers, on which I had all of the data and none of the software or configurations backed up. (I’m wiser now.)

I struggled figuring out how to get Skeinforge running again now, in part because I think the instructions that come with it never got updated as its capabilities did. No, I am not going to copy the STL into the system executable directory every time I want to slice something and then move the resulting G-code back out. It turns out that any version of Skeinforge that I might actually want to run has a file browser and remembers where you browsed the last time you used it; so it’s pretty easy to get along with.

And as to which version I actually want to run, one of the files I did have backed up was my detailed notes on fine-tuning Skeinforge settings for my CupCake, which (naturally) included the fact that I was running Skeinforge 0035. So there we go.

3D printer calibration objects

With slicing working, that just leaves calibration, and I’ve done that now too.

Last weekend … the weekend before? (Time flies / Doesn’t seem a minute) … I used my favorite calibration set, coasterman’s Essential Calibration set, to (re)calibrate Skeinforge to my CupCake.

The first thin-wall box (upper left) is printed with Skeinforge’s default settings, which aren’t even for a CupCake, and was extruding way too much plastic. The second is printed after clicking in all of MakerBot’s published CupCake defaults, and was good enough for me.

The 20-mm infill boxes test the Infill Solidity setting, which I always mix up and take in the wrong direction before going the right direction. 1.7 gives a beautiful, smooth upper surface to my infill.

Bridging (lower left) is … something I’m not going to try too hard to adjust right now. It works-ish. The perimeter-width calibration objects fit together on the first try. The Oozebane tuning to reduce stringing as the nozzle moves from one print area to another … does nothing for me, and never has.

And then I was ready to print, so print I did!

3D-printed brackets

The first non-calibration object I printed was this bracket I designed for 2020 aluminum extrusion (left). It doesn’t look so great. Let me tell you what’s wrong with it: … No, let me take the shorter approach of telling you what’s right with it: The two-hour print completed with no hitches. That is one hideous print.

I reprinted it with the Comb module activated (right), so that when it needs to move the nozzle from one area to another, it takes a path over the printed area instead of over open space, completely eliminating stringing. From the print areas. Comb completely eliminates stringing from the print areas. But Comb is executed (in the current toolchain configuration) before Raft; and Raft is the module that generates the support material that I was trying out in Skeinforge for my first time evar; so you still get stringing to and from the support material (and not even optimized for the shortest hop across open air). That’s handy.

3D-printed bracket with Skeinforge support material

And that support structure (front right) is … not what we’re used to in 2020. It’s actually not too bad — it uses material pretty efficiently; it generally is only generated where needed; and it generally detaches pretty easily. But it looks very different.

Also you can see how blobby and irregular the print is. Because the CupCake is horrible and incapable of printing smoothly? What if this is the best I can ever get?? All this effort … !!! … !!!

But I didn’t believe that. I’ve made smooth prints before; what’s the difference? The difference is that this object requires hopping the nozzle from area to area a lot; and rapidly stopping and restarting extrusion during nozzle hops are what a DC gearmotor extruder is worst at. With a stepper extruder, this part would be glorious!

Prove it!, you say. Fine; I’ll CAD up a part in which each layer has all smooth curves and no jumps, and we’ll see how gloriously it comes out.

There you go. The strands on the top layer are where the Y axis snagged and skipped steps and everything went poo; but otherwise, that’s a smooth print, photographed with the camera handheld in order to cause enough blur that you can’t prove otherwise.

It does, however, have very noticeable shrinkage from about 2 mm ≤ Z ≤ 4 mm. That, my dear friends, corresponds to when I opened the door to the garage to go work on something while still listening to the printer in case of problems. The blast of cold air from the garage shrank the ABS immediately — and more on the front of the print than the back.

3D-printed test object

Here’s a reprint with the dimensions reduced slightly to avoid the previous snagging when the build platform is at the absolute extremes of its range of travel, and with the entire build chamber enclosed by cardboard and plexiglass. There’s still some irregular shrinkage that I’m going to have to figure out, and just a bit more stringing that wasn’t completely eliminated. But this is not too bad.

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