Rivetback H-6

A sentry that holds one stance. 50 printed pieces key into each other — no screws, no glue, no pins.

Six legs on six fixed stations, an armoured deck over a charcoal chassis, a forward cannon and a sensor triplet. Nothing on it turns. Every structural joint is a rectangle cut so that it only goes in one way, which is why there is no fastener anywhere in the kit.

  • 50printed pieces
  • 15shapes to print
  • 5.4 ozassembled
Rivetback H-6 head on: a low yellow armoured deck carried on six splayed charcoal legs, a cyan crescent at each knee, and a short cannon centred on the deck pointing at the viewer.
Front elevation: 9.0 × 5.8 × 3.5 in over the feet, with 1.3 in of clear air under the chassis. The legs are one 7-piece design repeated at six fixed stations around it.

Apart

50 printed pieces in 15 shapes. 42 of them are 6 copies of one 7-piece leg.

The deck

The chassis lands first — 78 × 92 × 18 mm of charcoal — then three armour plates 88 mm across, layered fore to aft with the gaps between them left open.

Six stations

Six hip yokes key into the chassis edge. The key is 8.0 mm wide and its socket is drawn 0.25 mm oversize on each side, the same clearance every structural joint on the machine is cut to.

One leg, six times

Beam, armour, beam, armour, conduit, foot. Those six follow the yoke, and the whole leg repeats at 6 fixed angles — there are no left-hand and right-hand versions to sort.

The crown

Hub, barrel, sensor, collar. 61 mm of printed barrel seated on the pedestal, aimed out over the front plate.

Standing

9.0 × 5.8 × 3.5 in, 5.4 oz, and not one joint on it moves. It gets placed, and then it stays placed.

The joint is a rectangle

8 × 6 mm

Every structural joint on the machine is the same idea. A rectangular tenon, 8 × 6 mm, drops into a mortise cut 0.25 mm oversize on each side. A rectangle that is not square will not go in turned a quarter, so the part is keyed by its own section: there is no tab to line up, no arrow to read, and no way to get a leg on backwards and only find out at the end.

Leg armour uses the small version of the same rule, a 4.0 mm peg with 0.2 mm of clearance per side. Walls are never thinner than 1.2 mm and never thinner than 2.0 mm where a socket takes load, which is three and five passes of a 0.4 mm nozzle. Each piece is drawn standing in the orientation it prints in, so no joint needs support inside it.

One shape in the kit is not used. A lock pin was drawn for these joints and then left out of the assembly after the interference review found the keyed joints were the cleaner static answer. It is still in the files: print it as a spare, or do not print it at all.

Section through a keyed tenon, drawn at eighteen pixels to the millimetre: an eight by six millimetre rectangle sitting in a mortise a quarter of a millimetre larger on every side, and beside it the same rectangle turned a quarter turn, standing taller than the mortise is deep. 8 × 6 mm tenon mortise 0.25 mm clear a quarter turn out will not enter
Section at true proportion. Because the rectangle is not square, the wrong way round is not a tight fit — it is not a fit.
Close view of the near legs: charcoal beams with yellow armour plates keyed along the top, a cyan crescent bridging the knee, and a broad wedge foot flat on the floor.
Near legs. The yellow plate on each beam and the cyan crescent at the knee are separate pieces, which is how the three colours happen without a multi-material printer.

The crescent is the only part on the machine that carries nothing. It is 4 mm thick, it sits across the knee, and it is there so the leg reads as plumbing rather than as one solid casting.

The feet end in a broad sole and a rounded wedge rather than a point, and all six soles sit on a single plane in the model.

What you print

50
Every shape, and how many of each.
Chassis corecharcoal1
Carapace, foreyellow1
Carapace, centreyellow1
Carapace, aftyellow1
Hub pedestalcharcoal1
Cannon bodycharcoal1
Muzzle collaryellow1
Sensor insertcyan1
Hip yokecharcoal6
Upper leg beamcharcoal6
Upper leg armouryellow6
Lower leg beamcharcoal6
Lower leg armouryellow6
Conduit crescentcyan6
Footcharcoal6
15 shapes, plus the lock pin you can skip50
  • Standing size9.0 × 5.8 × 3.5 in
  • Assembled weight5.4 oz
  • Print time, all pieces15.9 h
  • Largest piece87 × 92 × 18 mm
  • Build plate needed180 × 180 × 180 mm
  • Nozzle0.4 mm
  • Thinnest wall1.2 mm
  • Wall at a loaded socket2.0 mm
  • Clearance, structural tenon0.25 mm
  • Clearance, armour peg0.2 mm
  • Charcoal pieces27
  • Yellow pieces16
  • Cyan pieces7

Print it once, key it together, and set it down.