CAD for fabrication

• Build a parameterized part around functional datums and process-aware dimensions.
• Prepare a fabrication and inspection plan that preserves critical interfaces.

• engineering-workflow
• tolerances-fits

CAD is a compact statement of design intent, not merely a picture. A useful model says which dimensions control function and which geometry should update together. If a screen frame changes width, centered mounting holes should remain centered because they reference a midplane or explicit parameter, not a chain of arbitrary offsets. Stable intent makes revisions predictable.

Begin with datums: surfaces, axes, or planes from which important dimensions are measured. Constrain sketches until their remaining freedom is intentional. Name parameters such as shaft_diameter, wall, and hole_spacing, then derive repeated geometry from them. Avoid long tolerance chains. If feature C must align with feature A, dimension C from A rather than through unrelated feature B. For fabrication, minimum wall, tool diameter, kerf, layer direction, support access, bend radius, and fastener installation space are as real as the nominal shape.

The selected process changes the design. A milled internal corner inherits cutter radius; a laser-cut slot receives kerf and has nearly vertical walls; a fused-filament print may bridge short gaps but produces anisotropic layers and often undersized horizontal holes. Add sacrificial tabs, fillets, chamfers, or inspection faces only when they serve a named need. The build decision is to preserve a camera's optical-axis location while allowing noncritical enclosure edges wider tolerance, rather than applying expensive precision everywhere.

A common failure is exporting a visually correct mesh with wrong units or inadequate tessellation. Another is “fixing” a manufactured part by editing several unrelated dimensions instead of updating the governing parameter. Before fabrication, inspect overall size, wall thickness, clearances, orientation, and units. After fabrication, compare actual critical dimensions with their acceptance limits. A beautiful render cannot show hidden tool access, support scars, weak layer orientation, or whether a connector can be inserted.

Problem

A laser-cut linkage needs 100.0 ± 0.2 mm center distance. Two holes are each located from opposite outer edges of a 130.0 ± 0.4 mm plate by 15.0 ± 0.2 mm. Find worst-case center-distance tolerance and improve the dimension scheme.

Steps

1. The chained center distance is plate width minus both edge offsets: 130.0 - 15.0 - 15.0 = 100.0 mm.
2. Worst-case variation adds absolute limits: ±(0.4 + 0.2 + 0.2) = ±0.8 mm.
3. Dimension one hole as datum and the second directly at 100.0 ± 0.2 mm; let noncritical edge margins absorb plate-width variation.

Result

The original chain permits 99.2–100.8 mm, while direct functional dimensioning controls the required 99.8–100.2 mm spacing.

Sanity check

Nominal geometry is unchanged; only the tolerance path changes, which is exactly the point of design intent.

A milled rectangular pocket must accept a perfectly sharp-cornered insert. What issue should be addressed in the CAD design?

A. The cutter leaves internal corner radii B. The pocket automatically shrinks equally everywhere C. CAD removes all process limits D. More decimal places create sharp corners

Your answer: ______________________________

Reasoning:

Goal

Create and inspect a process-aware mounting plate revision.

Equipment

• Any parametric CAD tool
• Printer or paper template
• Calipers or ruler
• Sample fastener and connector

Procedure

1. Define named parameters for plate width, hole spacing, fastener clearance, and connector keep-out.
2. Sketch from a central datum, fully constrain functional features, and predict which dimensions change when width is increased 10 mm.
3. Print a 1:1 paper template or fabricate a low-cost coupon; verify scale and test physical access with unpowered components.
4. Deliberate fault: export once with an intentionally wrong unit assumption; diagnose it using one known overall dimension before fabrication.

What to observe

• Expected: parameter changes preserve hole alignment and keep-out relationships while noncritical edges move.
• Measure: actual template scale and accessible clearances; a paper check validates layout, not strength or final process accuracy.

Transfer challenge

Revise a sensor bracket for a second board width using parameters, and identify which interface dimensions must not move.

Cautions

• Keep electronics unpowered during physical fit checks and do not fabricate until export units are verified.

Learner: ____________________ Date: ____________________

Evidence artifact or file: ____________________________________________

Notes: