I've been looking at FAI style rocketry building a fair bit recently and doing some explorations. I'm not aiming to compete and my motivation is more that I want a cheap and light rocket with lots of internal volume for a weird deployable idea I have, more on that another time. The rocket above is a cardstock rocket which is bulkhead/centring ring free and pretty lightweight. When it came to the nosecone I wanted to keep it pretty short and stubby and in keeping with the FAI look. But I also wanted to keep it light. If you want to go really light with 3D printing then "vase mode", where you have a single perimeter printed in a continually raising Z axis coil (rather than a layer then a Z lift) is a great approach. However, a problem with vase mode is what happens when you get to flatter top areas that are over 45 degrees from vertical, essentially the vase approach fails as it can't print the geometry. Below is probably the best I could get it.
So the workaround, I redesigned the CAD model of the nosecone into 2 sections, one section that would vase print well but with the tip removed and printed separately in a standard print approach with a small amount of infill. Below you can see the vase mode print complete with the tiny shoulder section (at the top) which steps in 0.3mm which is the thickness of the cardstock body tube.
Below you can see the vase mode section and then the standard print mode tip. Printed in PETG and ready for assembly with a spot of superglue.
I'm pretty pleased with the approach, the rocket I'm building is slightly larger than the FAI style 40mm diameter body tube as I used some PVC pipe and a 3D printed section as a mandrel for the body tube and transition. Some research indicates that for 40mm FAI rockets the nosecone, without the shoulder, is around 1.5g. I could lighten the tip section of mine some more, I also could sand and polish the PETG print a lot and it already contains a working shoulder section so I actually think this approach is not far of being competitive with this first, larger sized one, at 3.26g. I'm pretty sure at 40mm diameter with some work I could get these under 2g similar to the vacuum formed styrene ones with paper shoulders that people seem to use. Of course a pointier geometry means you could entirely vase mode a very light nosecone as I did on my UK altitude record holding "Imp" rocket design.
