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Designing real parts07 / 31

Functional features

Named shapes you add to a part to make it work: mounting, stiffness, sealing, or grip. Reach for them by name and the geometry follows.

Boss

Cylindrical protrusion with a hole, usually for a screw or heat-set insert. The "where parts bolt together" feature.

Rib

A thin reinforcing fin running along a surface. Stops a flat plate from flexing without doubling the wall thickness.

Pocket

Rectangular cavity in a solid. Cable channels, captive nuts, lightening holes.

Lip / Flange

An edge that overhangs the wall below. The rim on a container, the mounting plate on a motor.

Gusset

Triangular brace between two perpendicular surfaces. Stiffens a wall without much material.

Standoff

Threaded pillar that holds something at a distance. Hex outside, M3 inside is most common.

Spacer

Unthreaded sleeve that sets distance between two parts. The screw passes straight through.

Knurl

Textured grip pattern on a cylindrical surface. Thumb screws and adjustment knobs use it so fingers don't slip.

Designing real parts08 / 31

Text and labels on parts

Five ways to put a name, number, or icon on a printed part. Pick by depth and whether you need a second colour.

Raised text (embossed)

Letters rise ~1mm above the surface. Cleanest to print and easiest to read. The default when one colour is fine.

Sunken text (engraved / debossed)

Letters cut ~1mm into the surface. Robust against wear and scuffing, the go-to for serial numbers and stamped marks.

Flush text (multi-material inlay)

Pocket refilled with a second filament at the exact same height. Needs an MMU or a manual colour swap. Reads like a printed sticker.

Through-text (stencil / cutout)

Letters cut all the way through the plate. Perfect for signage that lets light through. Closed loops like "O" or "A" need a bridge or they fall out.

Segmented inlay (two-part assembly)

Print a plate with a text-shaped pocket and the letters as a separate piece. Glue them in a contrasting colour. Single-extruder friendly.

Designing real parts08 / 31

Text and labels on parts

Five ways to put a name, number, or icon on a printed part. Pick by depth and whether you need a second colour.

Raised text (embossed)

Letters rise ~1mm above the surface. Cleanest to print and easiest to read. The default when one colour is fine.

Sunken text (engraved / debossed)

Letters cut ~1mm into the surface. Robust against wear and scuffing, the go-to for serial numbers and stamped marks.

Flush text (multi-material inlay)

Pocket refilled with a second filament at the exact same height. Needs an MMU or a manual colour swap. Reads like a printed sticker.

Through-text (stencil / cutout)

Letters cut all the way through the plate. Perfect for signage that lets light through. Closed loops like "O" or "A" need a bridge or they fall out.

Segmented inlay (two-part assembly)

Print a plate with a text-shaped pocket and the letters as a separate piece. Glue them in a contrasting colour. Single-extruder friendly.

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GrandpaCADEnglish

A pocket reference

The 3D‑Print
Phrasebook

Plain words for asking AI to build the parts you want, the right way on the first try.

Preface

Why a phrasebook?

Every craft has its words. Carpenters say rabbet; knitters say purl; mechanics say chamfer. When you use the right word, the listener stops guessing and starts building.

AI is the same. Ask for "a thingy with a hole" and you get a shrug in 3D. Ask for "an M3 counterbore on a 5 mm wall" and you get a part. This little book is the words.

It works for GrandpaCAD. It also works for any other AI tool that generates 3D models or CAD code, because the vocabulary is the same: a fillet is a fillet whether the underlying engine is JSCAD, OpenSCAD, Fusion, or a sculpting model.

Shapes & operations (pages 1–5)

The pure CAD building blocks. Primitives, transformations, booleans, and edge or face features: the moves every modeller strings together.

Designing real parts (pages 6–21)

Functional features, holes, fits, fasteners, joints, motion hardware, hot ends, electronics, gridfinity, and the filaments they print in. Hardware your design has to fit around.

Prompting & printing (pages 22–29)

How to describe a part so the model builds it: dimensions, references, multi-step builds, iteration. Then export and slicer vocabulary for getting it onto a bed.

Read it cover-to-cover or jump to the page you need. Either way, keep it within arm's reach.

For Grandpa Franc, who built me things.

Contents

What's inside

Chapter01 / 31

Chapter 1

Shapes & operations

The pure CAD primitives and operations. Stack them, combine them, and the rest of the design follows.

Shapes & operations02 / 31

Primitives

The starting shapes for almost any design. Name them and you skip a lot of guessing.

Cube / Box

A six-sided block. Width, depth, height in millimetres.

Sphere

A ball. Specify radius or diameter, not both.

Cylinder

A tube or rod. Say hollow if you mean a pipe.

Cone

Tapers from a circle to a point. Truncated if it ends in a smaller circle.

Torus

A donut. Give the ring radius and the tube radius.

Wedge

A triangular prism. Ramps, brackets, and gussets start here.

Pyramid

Tapers from a polygon to a point. Square base by default.

Polyhedron

A custom mesh from points and faces. Last resort when nothing else fits.

Shapes & operations03 / 31

Transformations

How to move, turn, and reshape something that already exists. These compose, so order matters.

Translate / Move

Move along X (left/right), Y (front/back), or Z (up/down).

Rotate

Spin around an axis. Degrees unless you say otherwise.

Scale

Resize uniformly or per axis. Per-axis turns a sphere into an ellipsoid.

Mirror

Reflect across a plane. Good for symmetric parts.

Linear array

Duplicate along a vector. Count and spacing, not "a few".

Circular array

Duplicate around an axis. Count and the full sweep angle.

Offset

Grow or shrink a shape outward by a fixed distance. Inflates or deflates a profile in place.

Align / Anchor

Snap one face, edge, or corner to another. Removes the math from "centre on top".

Shapes & operations04 / 31

Boolean operations

Combine simple shapes to make complex ones. Most CAD models are booleans all the way down.

Union

Fuse two shapes into one solid. Overlapping volume becomes a single body.

Difference

Subtract one shape from another. The way you make holes and cutouts.

Intersection

Keep only the overlapping volume. Useful for trimming to a bounding shape.

Hull

Wrap a tight skin around a set of shapes. Quick organic blends.

Shapes & operations05 / 31

Edge and face features

Detail operations. These are what make a part look intentional instead of blocky.

Chamfer

A flat cut on an edge, usually 45°. Eases insertion and breaks sharp corners.

Fillet

A rounded edge. Stronger than a sharp corner, friendlier to touch.

Shell

Hollow a solid, leaving walls of a given thickness.

Extrude

Pull a 2D profile into 3D. The fastest path from sketch to volume.

Revolve

Spin a 2D profile around an axis. Bottles, knobs, and vases come from here.

Loft

Blend between two or more profiles. Smoothly changes cross-section.

Sweep

Drag a profile along a path. Pipes, handles, and grooves.

Draft / Taper

Slant a face by a few degrees. Helps prints release from supports.

Chapter06 / 31

Chapter 2

Designing real parts

How shapes turn into something printable: features, mating geometry, and the hardware your design has to fit around.

Designing real parts07 / 31

Functional features

Named shapes you add to a part to make it work: mounting, stiffness, sealing, or grip. Reach for them by name and the geometry follows.

Boss

Cylindrical protrusion with a hole, usually for a screw or heat-set insert. The "where parts bolt together" feature.