One of the places from which I get ideas for 3D printing is the Grasshopper public forum: Grasshopper Forum. Most of the people who post in this forum are architects, and several of them are highly expert at resolving problems people have with Grasshopper geometry definitions. One of them, Joseph Oster, provided a Grasshopper solution for defining the outer ribs on this building:

I thought the shapes of those ribs might make an interesting 3D container, so I downloaded Joseph’s Grasshopper file and made a number of changes to it so it could be used for 3D printing. Doing that was more difficult than I had expected, and I had to make several preliminary attempts before I was able to get anything that looked reasonable. I couldn’t quite duplicate the shapes of the building, but I was able to come up with something I thought worked pretty well. Here is a 3D rotation video of what I decided to print:

And here is the actual part at about 80% complete on my printer:

In spite of a couple of problems I had with it, here is the final part:

You can get the STL file for this part here:

The problems I had with this part are all related to the slicing process.

Slicer Failures

My slicer of choice is Craftware, which I have been using for for more than 2 years now. But when I tried slicing this STL file the program crashed after slicing about 3/4 of the part. So after that I tried my backup slicer, which is Simplify 3D.  That sliced the part OK, but for some reason closed off the top which made the resulting GCode unusable.

At that point I reverted to my emergency slicer, Kisslicer. I haven’t used Kisslicer in quite a while, but it did slice the part OK and that’s the result I printed.

Tool Path

When printing the part’s ribs, Kisslicer would do 3 – 5 adjacent ribs, and then move the printhead directly across the part and do 3- 5 more on the opposite side. It kept doing this for an entire layer, and then would repeat the process on the next layer.

This caused a significantly increase in print time due to all the cross-part moves, and it also added to the stringing problem.


Stringing is a problem that affects all 3D printers, but especially delta-style printers or those that use Bowden tubes to feed filament to their hotends. If you aren’t aware of what stringing is, here’s a typical example:

Well, for whatever reason, Kisslicer made a lot of strings on my part.  I spent some time removing them, but the results were not 100%.  Furthermore, Kisslicer did not do what I’d call a good job on many small areas of the print.

Compare this to a slightly modified version of the same part I sliced with Craftware and am printing now:


How I fixed the slicing problem

I changed the part’s geometry a little. Basically I changed the top and bottom shapes from ellipses to circles (a circle is just an ellipse with equal height & width), varied the twist values a tiny bit (surprisingly I had to tweak values out to the 3rd decimal place to get results that looked good), and added a few more ribs.

Why this allowed Craftware to slice the part I have no idea. But I have run into obscure geometry/slicing problems like this before.  In fact I’ve got a part that looks great but that none of my 3 slicers can slice properly.

Last Update: 08 Feb 2017