Neville Island helix

Instructions

Construction plan (PDF)

13 pages, 133 KB. Frames, braces, bracket elevations, roadbed cut sheets, build sequence, diagonal bracing. Page 13: half-lap screw template.

Half-lap screw template (PDF)

US Letter, 51 KB. Print at 100% / Actual size, then check the 2 in and 50 mm bars. Six #6 × 5/8 screws per lap.

Build status

As-built heights and datums, frame alignment, shop process, fasteners, every fixture, and open items. Overrides the PDF where they differ.

Design handoff (Markdown)

Design rationale, alternatives considered, and formulas behind the locked plan.

Read the plan first, then the build status. The plan's entry pages (2, 3, 8) are out of date; the build status has the current entry geometry.

Printed fixtures (STL index)

46 files, all modelled in millimetres and checked as watertight single bodies. Extents are the bounding box as exported (X × Y × Z). Unless the build status marks a part tested, it has only been verified in software.

Printing: Creality Print 7.3, 260 mm bed. Templates print router face down, 2–3 walls, 10–15% infill, no supports. For the 3MF files, if the modifier doesn't come in, import the body and its _CORE100 STL together as one object, set the core to Modifier, and give it 100% infill.

File	Size	Extents	Script	Notes
Router templates
`roadbed_halflap_template_A.3mf`	124 KB	3MF project (body + modifier)	`make_lap_template.py`	Half-lap router template, hands A and B. Hooks the end cut and the 26 in edge; window to a radial shoulder at 3.75°. Open the 3MF (body + 100% core modifier).
`roadbed_halflap_template_A.stl`	619 KB	203.8 × 184.4 × 25.4 mm 8.03 × 7.26 × 1.00 in
`roadbed_halflap_template_A_CORE100.stl`	13 KB	198.6 × 67.5 × 12.7 mm 7.82 × 2.66 × 0.50 in
`roadbed_halflap_template_B.3mf`	127 KB	3MF project (body + modifier)
`roadbed_halflap_template_B.stl`	632 KB	203.8 × 184.4 × 25.4 mm 8.03 × 7.26 × 1.00 in
`roadbed_halflap_template_B_CORE100.stl`	13 KB	198.6 × 67.5 × 12.7 mm 7.82 × 2.66 × 0.50 in
`bracket_pocket_template_A.3mf`	138 KB	3MF project (body + modifier)	`make_bracket_pocket_template.py`	Bracket pocket at a lap joint: slot 0.6625 wide on the joint line, 3/32 deep, 1/2 in bit. Pair with the same lap letter.
`bracket_pocket_template_A.stl`	715 KB	150.4 × 168.1 × 31.8 mm 5.92 × 6.62 × 1.25 in
`bracket_pocket_template_A_CORE100.stl`	2 KB	126.5 × 33.6 × 19.0 mm 4.98 × 1.32 × 0.75 in
`bracket_pocket_template_B.3mf`	140 KB	3MF project (body + modifier)
`bracket_pocket_template_B.stl`	726 KB	150.4 × 168.1 × 31.8 mm 5.92 × 6.62 × 1.25 in
`bracket_pocket_template_B_CORE100.stl`	2 KB	126.5 × 33.6 × 19.0 mm 4.98 × 1.32 × 0.75 in
`bracket_pocket_template_MID.3mf`	63 KB	3MF project (body + modifier)	`make_mid_pocket_template.py`	Mid-piece bracket pocket (odd n). Rides the 26 in edge; center the V-notch on the pencil line (chord 20.683, P1 19.900).
`bracket_pocket_template_MID.stl`	327 KB	147.9 × 158.1 × 31.8 mm 5.82 × 6.23 × 1.25 in
`bracket_pocket_template_MID_CORE100.stl`	2 KB	125.6 × 29.5 × 19.0 mm 4.95 × 1.16 × 0.75 in
`router_depth_block.stl`	1.4 MB	172.3 × 25.4 × 104.1 mm 6.78 × 1.00 × 4.10 in	`make_router_depth_block.py`	Two-sided depth block, wells 3/32 · 1/4 · 3/8 / 1/2 · 5/8 · 3/4. Print on its end with a brim.
`router_depth_gauge.stl`	231 KB	76.2 × 31.8 × 12.7 mm 3.00 × 1.25 × 0.50 in	`make_router_depth_gauge.py`	Checks POCKET 3/32, LOWER 1/4, UPPER 1/2 (3/4-stock values).
Heights
`p1_height_template.stl`	149 KB	38.1 × 50.8 × 26.2 mm 1.50 × 2.00 × 1.03 in	`make_height_spacers.py`	P1 roadbed top at bracket 0: 1-1/32 in above the deck.
`height_base_1_4in.stl`	122 KB	38.1 × 50.8 × 6.3 mm 1.50 × 2.00 × 0.25 in	`make_height_spacers.py`	Stacking height blocks (pegs + crush ribs). Template + 1/2 in per 45° marks the plywood top.
`height_spacer_1_4in.stl`	105 KB	38.1 × 50.8 × 9.4 mm 1.50 × 2.00 × 0.37 in
`height_spacer_1_2in.stl`	112 KB	38.1 × 50.8 × 15.7 mm 1.50 × 2.00 × 0.62 in
`height_spacer_3_4in.stl`	122 KB	38.1 × 50.8 × 22.0 mm 1.50 × 2.00 × 0.87 in
`height_spacer_1in.stl`	98 KB	38.1 × 50.8 × 28.4 mm 1.50 × 2.00 × 1.12 in
`height_spacer_1_1_2in.stl`	118 KB	38.1 × 50.8 × 41.1 mm 1.50 × 2.00 × 1.62 in
`first_loop_pier_post2.stl`	77 KB	101.6 × 38.1 × 20.3 mm 4.00 × 1.50 × 0.80 in	`make_first_loop_piers.py`	First-loop piers, posts 2–7. Top at grade, arrow uphill; two screw tabs.
`first_loop_pier_post3.stl`	91 KB	101.6 × 38.1 × 33.0 mm 4.00 × 1.50 × 1.30 in
`first_loop_pier_post4.stl`	82 KB	101.6 × 38.1 × 45.7 mm 4.00 × 1.50 × 1.80 in
`first_loop_pier_post5.stl`	97 KB	101.6 × 38.1 × 58.4 mm 4.00 × 1.50 × 2.30 in
`first_loop_pier_post6.stl`	107 KB	101.6 × 38.1 × 71.1 mm 4.00 × 1.50 × 2.80 in
`first_loop_pier_post7.stl`	97 KB	101.6 × 38.1 × 83.8 mm 4.00 × 1.50 × 3.30 in
`layer_spacer_4in_pitch.stl`	63 KB	38.1 × 38.1 × 83.3 mm 1.50 × 1.50 × 3.28 in	`make_layer_spacer.py`	Loop-to-loop check, 3.280 in (4.000 − 0.72). Normal mode, ~22 g.
`layer_spacer_4in_pitch_vase.stl`	100 KB	38.1 × 38.1 × 83.3 mm 1.50 × 1.50 × 3.28 in	`make_layer_spacer_vase.py`	Same spacer in spiral vase mode (~10 g, or ~4 g single line). Slice gap closing radius 0.01.
`layer_spacer_4in_pitch_vase_1line.stl`	28 KB	38.1 × 38.1 × 83.3 mm 1.50 × 1.50 × 3.28 in	`make_layer_spacer_vase.py`
Entry
`entry_wedge_riser_inside.stl`	28 KB	25.4 × 57.2 × 32.0 mm 1.00 × 2.25 × 1.26 in	none kept	Tongue risers, 1 × 2.25 in, 1.261 tall, step 0.864. Engraved R / L.
`entry_wedge_riser_outside.stl`	24 KB	25.4 × 57.2 × 32.0 mm 1.00 × 2.25 × 1.26 in	none kept
`cork_to_plywood_transition_shim.stl`	68 KB	50.8 × 88.9 × 15.5 mm 2.00 × 3.50 × 0.61 in	none kept	The “offset bracket” under P1: low foot 0.375 (tongue), high foot 0.611 (P1). Sits in a ~0.300 deep deck pocket.
`corner_spacer_P1.stl`	28 KB	15.9 × 15.9 × 9.6 mm 0.62 × 0.62 × 0.38 in	`make_corner_offset_spacer.py`	Barrel under each P1 wing corner, 0.376 tall (0.311 + 1.65 mm field correction), 5/8 OD. Print 2 at 100% infill.
Brackets
`bracket_edge_shim.stl`	13 KB	7.0 × 38.1 × 15.9 mm 0.27 × 1.50 × 0.63 in	`make_bracket_edge_shim.py`	Fills the 26 in edge to 2x4 face gap above the bend; also the radial go/no-go gauge. 29 needed.
`bracket_plumb_shim.stl`	2 KB	88.9 × 15.7 × 0.6 mm 3.50 × 0.62 × 0.02 in	`make_bracket_plumb_shim.py`	Tapered strip (0.20 → 0.56 mm) for the sideways lean from grade. Notched edge uphill. One per bracket.
`bracket_wedge_gap_1_64.stl`	2 KB	88.9 × 0.8 × 15.7 mm 3.50 × 0.03 × 0.62 in	`make_bracket_wedges.py`	Wedges for a gap between the bracket leg and the post; notches = gap in 64ths.
`bracket_wedge_gap_2_64.stl`	3 KB	88.9 × 1.2 × 15.7 mm 3.50 × 0.05 × 0.62 in
`bracket_wedge_gap_3_64.stl`	4 KB	88.9 × 1.5 × 15.7 mm 3.50 × 0.06 × 0.62 in
`bracket_wedge_gap_4_64.stl`	5 KB	88.9 × 1.9 × 15.7 mm 3.50 × 0.07 × 0.62 in
Shop tool
`router_sigerio_test_plate.stl`	502 KB	152.4 × 152.4 × 4.8 mm 6.00 × 6.00 × 0.19 in	none kept	MW104 router to Sigerio circle-jig adapter, test plate. Hole sizes and center bore are estimates.
`router_sigerio_test_plate_body.stl`	440 KB	152.4 × 152.4 × 4.8 mm 6.00 × 6.00 × 0.19 in
`router_sigerio_test_plate_screw_rings.stl`	563 KB	98.9 × 98.9 × 4.8 mm 3.89 × 3.89 × 0.19 in

Obsolete, not published: bracket_pocket_template.stl, entry_transition_shim.stl, entry_transition_shim_inside.stl, entry_transition_shim_outside.stl, entry_wedge_riser.stl.

Scripts need Python with numpy trimesh manifold3d shapely mapbox_earcut scipy rtree networkx matplotlib pymupdf pypdf. Their output paths point at the original working folder; change them before running.