This is a replica of the Sentinel model rocket sold by Estes from 1988 through 1994. It is one of my favorite rockets. The photo shows the original Sentinel on the left, and the 3D printed version on the right. The original is 27" tall, the printed one is 21.5"

I scaled it down by .8 so the fin section would fit within the 6" diameter build plate of my Orion Delta printer. The body wall is 1 mm thick, allowing for two extrusions of .5mm.

If your printer's build plate is 8" diameter or greater, you can scale the rocket up by 1.25 in your slicer and use an extrusion width of .625 to print it at full original size.

I have not flown this rocket, so proceed at your own risk if you decide to do so. At the .8 scale, It should be possible to use BT-55 centering rings to make a motor mount that would be held in place between the bayonet fitting on the mid section and the retainer ring built into the bottom of the fin section. You would need to file/cut 4 notches in the rings to get them past the bayonet bumps in the fin section. Don't make the notches too large - you don't want the ejection gasses to escape out the rear of the rocket before they can eject the parachute! If printed with 1.25 scale multiplier, BT-60 centering rings should work. Always check your CG/CP locations !

Parts connect with bayonet fittings. Line up channels with bumps, insert and twist 90 degrees clockwise until you feel it snap in place.

The "fore" section has an internal lug that can be used to attach a shock cord. You will need to use a piece of stiff wire to thread a cord though the lug.

Update 5/3/2018: Updated some parts to orient them correctly for printing. It is no longer necessary to rotate them after importing them into your slicer. Also enlarged the launch lugs to make sure a 1/8 inch rod will fit even when rocket is not scaled up.

Update 5/7/2018: Added Fin2 alternate fin section. This should be printed with zero infill and either 1 perimeter for lightweight, or 2 perimeters for strength. Use 5 solid bottom layers so the built-in rafts on the three boosters will provide adequate support. Use 0 top solid layers to prevent Slic3r from trying to cap off the booster nozzles. Remove the rafts after print is done.

SeeMeCNC

ORION Delta 3D Printer

.2mm layers

See Slic3r settings

See included Slic3r settings zip file

Copy the Slic3r settings files into the filament/print/printer folders at
C:Users > yourID > AppData > Roaming > Slic3r

NOTE: You must print each part in the orientation shown in the second photo to avoid need for support.

The "extra length on restart" setting is necessary to maintain priming of the hot-end and avoid under-extrusion during the numerous travel moves on the fin section.

The base.stl part is the base of the nose cone - one end locks into the nose cone, the other end slip-fits into the "fore.stl" section.

If the bayonet fittings are too tight, don't force them as this can cause the plastic to friction-weld together and you might not get them apart again. Instead, use some sandpaper to sand the grooves a bit, and use a candle to rub some paraffin onto them as lubricant.

The fins have some pretty serious overhang, so the leading edge may need some post-print smoothing. If you just cannot get them to behave, you might need to go ahead and use some support. This is where you find out just how well-behaved your PLA really is. For me, the MARS PLA did really well, while the SeeMeCNC blue PLA needed a lot more cleanup.

The tip of the nose cone will likely be wobbly due to heat build-up, so be prepared to clean it up with a knife.