Multicolor 3D printing a rocket?

OpenRocket simulation of my 2.6" BFR with 24 mm engine mount showing semi-transparent fans

While struggling with taping and painting the BFR rocket it occurred to me I could use my newfound multicolor 3D printing skills for rocketry.  I checked Amazon and ordered metallic silver and metallic black filaments to try printing the BFR (only) and make a D/E powered rocket as described by jgutz20.  The new filaments are coming overnight, then I'll try slicing the nose and tail and see if I can find a good point to swap filaments.  I'll start with printing the nose to see how it looks.  I could try to match the filament colors with painting a BT-80 body tube, or just 3D print one!  I'll try designing that to see how much it weighs.

Printing the nose cone and tail so the colors split at the fins necessitates flipping the objects 90 degrees in UltiMaker Cura before slicing and then printing them horizontally instead of vertically (compare this picture with my earlier vertical print of the nose cone shown in the second picture):

The second layer is visible on the rocket and the inner tree supports

Separately, I've printed some "clear" fins using "Transparent PLA" to add to jgutz20's model because that greatly stabilizes the rocket in OpenRocket.  I used OpenRocket to lay out fins that were big enough to stabilize the rocket then exported them as .OBJ files for 3D printing.  My goal is to 3D print jgutz20's base after "cutting" slots in it using Tinkercad or learning to use Fusion 360, rather than try to saw through the PVC base.  I also want to modify the centering rings, adding supports to hold the fin tabs, so I don't have to glue them in place permanently if they're not completely transparent.  I did something like this years ago when building a flying Cherry Coke bottle rocket for my daughter, though I cut those fins from a sheet of plexiglass using a hack saw and don't want to have to go through that process again!

This will be a work-in-progress posting so please check back from time to time!

February 28th update:

The 3D print with filament swap (using Cura's Pause at Height script at Layer 166 of 330, as described in my previous post) completed after a 9 hour 15 minute print job (swapping filaments at 5 hours and 10 minutes).  Several things were quickly evident, including that the bottom wasn't round but had a flat surface where it contacted the printer bed (see below).  This is a consequence of me having to lay the print job on it's side instead if printing upright, from bottom to top.  This also led to some imperfections in the top surface as well (2nd photo, below).  Equally troubling, when looking at the base from above (3rd photo, below) it's clear the sides are cracked in several places (at "2 o'clock" and "10 o'clock" and "11 o'clock" on the photo).  This may be something I could stabilize by glueing these pieces together but it's clear that printing this object sideways, as needed to enable multicolor 3D printing, will not give a suitable build to provide parts for a model that will be subjected to lots of force during flight and recovery.

Top of finished multicolor printed BFR nose cone

Finished top of multicolor 3D printed nose cone

Finished multicolor 3D printed nose cone view from the bottom

I did find a use for this 3D printed failure:  I used it to test painting some "windows" using Testors enamel paint and a thin brush.  After testing on the 3D two tone print, I painted the nose cone of my SpaceX BFR Super Heavy model.  I learned to do the large stripes behind the cockpit windows but will need some thin Frog tape or other masking tape to cover the windows and paint them to look as nice as jgutz20's version.

Painting windows on my spray painted BFR (on right) after testing on 3D printed two tone BFR (on left)

Conclusion:

The experiment failed, but was a valuable lesson.  The next steps would be to either print the nose and tail using just the "metallic silver" filament I ordered, then paint the backs with black spray paint.  This would eliminate having to paint one side.  Another option would be to digitally slice the nose and tail vertically, print each half separately (upright), then glue the halves together.  It was an interesting attempt to use my newfound skills.  I'll have to find another way to put my multicolor 3D printing skills to use for rocketry!

Unfortunately, when I tried printing the whole nose cone with this "metallic silver" filament it snapped while removing from the print surface after almost 12 hours of printing!  I was using Giantarm's "Silk Silver" PLA filament, 1.75 mm, printed at 195 C (recommended 195~230 C) using 15% infill.  I purchased this filament from Amazon earlier this week.  The tree supports were brittle, and the nose cone itself had several other forming fractures where it looked like it would crack if dropped/stressed.  I could try reprinting it using 100% infill and/or try a higher temperature, or just go back to using standard white or gray PLA and painting the nose cone to get the desired look as before.

Fragile print SNAPPED when trying to remove from printer bed

March 4 update:

Vindication!  Well, not for the multicolor BFR rocket but I found another project, a recently designed Gemini Joe Mini by Jamie Claye on Printables.com, that encourages a two-tone print of the nose cone if possible.  I still have to assemble this (smaller) rocket but I took the creator's suggestion and edited the gcode generated by UltiMaker Cura to include a Pause at Height script, beeping and giving me a 2 minute pause to change from white to black filament.  I made sure to keep the standby temperature at 195 C, and used the same black silk filament I'd tried above.  Here's the nose cone printed:

After trimming, it gives a respectable print with no signs of cracking.

I think I need to revisit printing the black and silver silk filaments at a higher temperature (215 or 220 C), as suggested on Reddit.

March 6th update:

Since the silver silk filament was a "sunk cost", I tried printing the BFR nose at 220 C, both horizontal so I could change filaments and vertical with just the silky silver filament (at 220 C) with the same result.  The prints are unusable, and the vertical printing came apart like a slinky when trying to detach from the print bed.  I found comments on Thingivese from another developer, mech-G, who posted plans for a cool looking SciFi rocket with the comment, "I do not recommend the Silky Silver for flyable rockets because the interlayer adhesion is weak compared to other PLA's, even when printed at higher temperatures."  He recommends printing with white PLA and painting with Rustoleum Silver Metallic paint, as I ended up doing with my SpaceX BFR Starship build.