Design jigs and replacement parts as parametric build123d scripts and export STLs that print right the first time. The deliverable is the STL: the printer matters only for whether the part fits the bed and which clearances hold, and both are parameters.
Running build123d
The scripts live in ${CLAUDE_SKILL_DIR}/scripts/ (this skill's folder). Run them
with uv, which needs no setup and works on any Python version:
uv run --with build123d python ${CLAUDE_SKILL_DIR}/scripts/spacing_block.py 10
Without uv: create a venv and pip install build123d, then run with that venv's
python. Write the STLs into the user's working directory (or where they ask), never
into the skill's own folder.
Ready scripts
All of them take --bed XxYxZ for a printer other than the default, -o for the output
name, and --help for every option and its default. The examples below shorten the
command to python scripts/...; run them the uv way shown above. Each script is
tested and ends in the print-readiness check, so its output needs no extra measuring.
scripts/circle_cutting_jig.py: a router trammel for discs and rings.
python scripts/circle_cutting_jig.py 300 250 --mount <BC>:<N> # ring: 300 OD, 250 ID
python scripts/circle_cutting_jig.py 200 --bit 12.7 # disc only, 1/2" bit
A plate screws to the router; an arm carries one pivot hole per cut, placed for the
bit (outer edge at D/2 + bit/2, inner edge at D/2 - bit/2), so the circle comes out at
the size asked for. Before running it, ask the user for two things you cannot assume:
the bit's cutting diameter, and the router sub-base screw pattern (bolt-circle
diameter <BC> and screw count <N>, measured on their router). If they cannot say
yet, generate it anyway with the 1/4" default bit and no --mount, and tell them both
assumptions: a plate without screw holes can be drilled using the router's own
sub-base as a template.
For a ring, the outer edge is cut first and the inner edge last: the inner cut frees the center disc that holds the pivot pin, so nothing can pivot after it. Tell the user so, and to fix the blank to a sacrificial board so neither piece shifts once cut free. The script prints the cut order too.
scripts/angle_wedge.py: holds work at an exact angle.
python scripts/angle_wedge.py 15
python scripts/angle_wedge.py 22.5 --depth 80 --width 40
Prints on its side so the slope is traced in XY, not stair-stepped by layers. Height
follows from the angle, never the reverse, so the angle is exact; if a steep angle
makes it too tall for the bed, the check refuses it and you should lower --depth.
scripts/spacing_block.py: setup and spacing blocks, single or matched sets.
python scripts/spacing_block.py 10
python scripts/spacing_block.py --set 5,10,15,20
Measuring faces stay flat (engraved label, side scallops, one chamfered corner as an orientation mark). Every block in a set rests on the bed. Heights that are not a multiple of the 0.2 mm layer height get a warning, because they cannot print exactly.
scripts/threaded_globe.py: a replacement threaded light globe (a hollow sphere
on a threaded collar that screws into the fixture, like a porch-light "fitter" globe).
python scripts/threaded_globe.py --inches --diameter 5.700 --height 6.2 \
--crest 3.235 --root 3.110 --pitch 0.232 --collar 0.713 --thread-length 0.700 \
--bore 2.825
python scripts/threaded_globe.py <same measurements> --collar-test # print this first
Every dimension comes from the user's calipers (see "Replacement parts" below). The
thread is rounded like glass threads, and --clearance (default 0.2 mm) takes a
little off its diameters so the print screws in. By default the globe splits at
the equator into two halves that join with a glued half-lap, each printed rim-down
so its supports stand inside where they barely show; a hollow sphere cannot print
whole without supports scarring its outside (--one-piece does it anyway).
Always suggest --collar-test first: about a seventh of the plastic, and it proves the
thread fits before committing to the full globe. Printed shades need an LED bulb; PETG softens near 80 C.
For an outdoor fixture, ASA stands up to sun better than PETG. --step adds a STEP file.
Replacement parts from a measured original
The original is the specification, so the measurements decide whether the part fits. Ask for caliper numbers; never estimate dimensions from a photo, which has no scale. Ask specifically for:
- Threads: the diameter over the crests, the diameter in the bottom of a groove (the root, measured on the part itself, not taken from the mating part), the pitch measured across several crests and divided by the number of gaps, the ridge shape (rounded or sharp), and the hand (does it screw in clockwise?).
- Every diameter that mates with something: openings, collars, bores.
- Overall height, and the height of each distinct section.
- What it must survive: heat from a bulb or motor, sunlight, water, load.
Sanity-check the numbers before modeling: a pitch longer than the threaded length, a root bigger than the crest, or parts that do not add up to the overall height are measuring slips. Ask about them rather than modeling them; the scripts refuse those cases. An earlier model of this same globe, built without these checks, took the root from the fixture's socket and got a thread 0.45 mm deep, where the glass's own groove measured 1.6 mm.
Custom jigs
Read references/build123d_patterns.md and references/printer_specs.md before
writing code; they hold the clearances, minimum sizes, and the build123d idioms that
keep a part on the bed. Then:
- Export with
export_checkedfromscripts/printcheck.py, not a bareexport_stl. Copyprintcheck.pynext to the custom script so the two travel together, rather than importing it from the skill's folder. It refuses an invalid shape, a solid that would print in mid-air, or a part too big for the bed at any rotation, and rotates the part when only a diagonal fits. It also warns about surfaces sloping past 45 degrees, which need supports. If it refuses, change the design (split a long jig into stages that register on each other, or shrink it); never hand over an STL it rejected. - Verify by measuring the solid, not by re-reading the code. Probe hole positions
with
is_inside, heights withbounding_box(), angles from a face's normal. An earlier version of this skill shipped scripts that ran cleanly and built a trammel with no pivot hole and a 45 degree wedge that measured 26.6; only measuring catches that.
Design rules that matter for woodworking
- Reference faces stay flat. Any face that sits on or against the work is a measuring surface. Engrave labels (never emboss) and put them on faces that do not touch the work.
- No knife edges. A tapered end thinner than about 1 mm will not print. Add a short vertical toe; it does not change the slope's angle.
- Precision features go in XY. Holes whose axis is vertical print round; slopes and angles drawn in the XY plane are as accurate as the printer gets. Orient the part so the dimension that matters is in XY.
- Clearance by fit. Pivot pins and bushings: +0.1 to 0.2 mm. Screws: +0.3 to 0.5 mm. Drill guides: the bit plus 0.1 to 0.2 mm, so the bit cannot wander.
- Split a hole row by indexing, not by a second jig. When a row of holes is longer than the bed, make a shorter jig and have the user move it along, dropping a pin through its first hole into the last hole already drilled. The spacing stays exact across the move.
- Mirror text on faces that print face-down. Text engraved on a face that sits on the bed in print orientation reads backwards when viewed from that side, unless the sketch is mirrored in the model.
- Repeated drilling wears plastic. A drill guide used more than a handful of times should take a steel bushing (press-fit, sized from the bushing's OD) rather than guide the bit in bare PLA.
Handing over the result
Give the user:
- the STL's full path, its size, and the solid count (from
export_checked's output) - print orientation (as exported: the STL is already in print orientation), perimeters and infill, and whether supports are needed and where: the export's overhang warning says (jigs usually need none; a sphere always does)
- which dimensions to check with calipers after printing, and, for anything that must fit (pins, hardware, bushings), a suggestion to print a small test piece of just that feature first; clearances vary between printers and filaments
If they may want to edit it in CAD later, also export a STEP with export_step.