Enclosure route 1 — 3D printed

The part that does not fit

cad/bottom_case.scad models the bottom shell as one 309 × 210 mm part. That is larger than every common print bed:

Printer	Bed (X × Y mm)	309 mm fits?
Creality Ender 3 / V3	220 × 220	no
Prusa MK4 / MK3S	250 × 210	no
Bambu X1 / P1 / A1	256 × 256	no
Prusa XL, Bambu H2D, Elegoo Neptune 4 Max	≥ 320	yes

So the case is printed as two halves, joined at the centreline (split_x in params.scad):

• Each half is 154.5 mm wide plus 10 mm of tabs — fits a 220 mm bed flat.
• Floor tabs: three dovetail tabs (tab_count, tab_w, tab_flare, tab_len) on the left half’s floor drop into matching pockets in the right half; pockets are grown by joint_gap (0.15 mm per face — tune with a 30 mm coupon).
• Wall half-lap: on the front and rear walls the left half’s outer half-thickness continues 8 mm past the seam; the right wall is recessed to match.
• Pins: two 3 mm holes through the laps take a length of filament or brass rod.
• The sled screws to four bosses, two per half — that is what makes the joined shell stiff; the tabs only locate it.
• The gasket ledge continues across the seam so it is not a dust path.
• half = "left" | "right" | "both" — "both" for a large-format printer.

The joint is verified every ./dev test: cad/tests/joint_intersection.scad renders the overlap of the two halves and scripts/check_cad_joint.py fails if it has any volume.

The eight printed parts

#	Part	File	Purpose	Qty
1	Bottom case, left	bottom_case.scad (half="left")	Shell, bosses, gasket ledge, vents, USB cutout, light-pipe aperture, foot recesses	1
2	Bottom case, right	bottom_case.scad (half="right")	as above	1
3	Pico mount bracket	pico_mount_bracket.scad	Cradle holding the Pico at a fixed height (Rev A only; Rev B mounts the Pico on the board)	1
4	FPC cable guide	fpc_cable_guide.scad (cable="keyboard"/"clickpad")	Enforces ≥ 5 mm bend radius on the FFC	2 + 1
5	Perfboard sled	perfboard_sled.scad	Tray with the common M2 hole pattern; holds Rev A stripboard or Rev B PCB; bridges the case seam	1
6	USB strain relief	usb_strain_relief.scad	Two-piece clamp (M2 bolts) gripping the cable jacket, screwed to the floor, so a pull loads the case, not the Pico’s connector	1 set
7	Tilt feet	tilt_feet.scad	Rear risers for a typing angle; front recesses take 10 mm rubber feet	2
8	ZIF support block	zif_support_block.scad (variant="keyboard"/"clickpad")	Backs up the FPC connectors against insertion force so they do not lift off the board	1 + 1
9	LED light pipe	led_light_pipe.scad	Carries the touchpad LED to the deck surface; printed in clear PETG or natural PLA	1

(Nine files, “eight parts” in the issues because the two case halves come from one source.)

All dimensions come from one shared file, cad/params.scad; values marked MEASURE are targets until the real X240 deck is measured (#44). No number may be duplicated across files. Render everything with ./dev build cad → out/cad/*.stl (OpenSCAD 2021.01 in Docker; PNG previews are not available headless — open the .scad in OpenSCAD to look).

Print settings

Part	Material	Layer	Walls	Infill	Supports	Notes
Case halves	PETG	0.20 mm	4	25 % gyroid	none, open side up	3–5 mm brim if corners lift
Sled, bracket, ZIF block	PETG	0.20 mm	3	30 %	none
Cable guide, strain relief	PETG	0.16 mm	3	40 %	none	small; print several
Tilt feet	PETG	0.20 mm	4	40 %	none	flat face down
Light pipe	clear PETG / natural PLA	0.12 mm	100 %	none	print standing	polish the tip

PETG over PLA for the case: higher heat deflection (a laptop deck in the sun) and less brittle at the dovetail. Estimated filament 120–180 g for the set.

Tolerances

Feature	Nominal	Printed allowance
M2 heat-set insert hole	3.2 mm	+0 — inserts want a snug hole
Dovetail	—	0.15 mm clearance per face; test with a 30 mm coupon before the full print
Alignment pins	3.0 mm	hole 3.2 mm
Sled to case bosses	M2	2.4 mm clearance holes in the sled
Gasket ledge	1.2 mm deep × 2.0 mm wide	foam tape is 1 mm; ledge leaves 0.2 mm compression
USB cutout	Micro-USB 8.5 × 3.5 / USB-C 9.5 × 4.0	+0.5 mm each way

Record actual measured-vs-designed values after the first dry-fit (issue #44); the table above becomes the tolerance report.

Assembly order for the printed route

1. Fit heat-set inserts into both halves and the sled.
2. Join the halves on the dovetail; push in the alignment pins.
3. Screw the sled across the seam — the case is now rigid.
4. Fit cable guides and ZIF support blocks to the sled.
5. Continue with integration.md.

No printer?

Commercial print services (Craftcloud, JLC3DP, Treatstock) will quote the split halves readily; a single 309 mm part is often refused or priced for an industrial machine. Expect $25–45 for the set in PETG. Or skip printing entirely: handmade.md.