Hand Tools and Joinery
Machines cut parts. Hand tools turn parts into an object. Almost every build in this class ends with measuring, drilling, clamping, gluing, and driving screws — and a build that was cut precisely can still come out crooked if it's assembled carelessly.
Measuring
Calipers are the tool that makes your CAD match reality. Almost every fit problem in this class starts with a dimension somebody guessed.
- Use calipers for anything that has to fit something else — material thickness, a bolt shaft, the inside of a cabinet, a printed part you're matching.
- Measure the same thing twice in two places. Plywood is not uniform, and a sheet can be 11.4 mm at one corner and 11.9 mm at another. When the two readings differ, decide which one your design should be built around — the tighter or the looser — rather than splitting the difference. If it's off by more than about 1 mm, use different stock.
- Write the measurement down when you take it. A number you remember is a number you'll get wrong.
- Use a tape measure for long spans, and read it against the same edge every time — the hook on the end slides on purpose.
Drilling
- Clamp the work. A part that spins when the bit catches is how hands get hurt. This applies to a hand drill, not just the drill press.
- Match the bit to the job. A hole for a screw shaft to pass through is bigger than a hole for a screw to bite into. Two different holes, two different bits.
- Back up the exit side with a scrap board to keep the far face from blowing out.
- Bare hands near the drill press. No gloves, no loose sleeves — see PPE.
Clamping and glue
- Dry-fit the whole assembly before any glue touches it. Glue-up is a timed event and it's the worst moment to discover a part is backwards.
- Clamp squarely, and check with a square rather than by eye. A cabinet glued out of square stays out of square.
- Glue is stronger than the wood on a long-grain joint and weak on an end- grain butt joint — which is why the joints below exist.
- Wipe squeeze-out while it's wet. Dried glue won't take finish and is miserable to sand off.
Which glue. Two different jobs:
- Titebond (yellow wood glue) for wood to wood. This is the default for everything in this class that's plywood on plywood. Clamp it, give it time, and wipe squeeze-out with a damp rag while it's still wet.
- Gorilla Glue (the polyurethane kind) for gluing unlike materials to each other — a printed part onto a wood panel, say, where wood glue has nothing to grab. It needs a trace of moisture to cure and it foams and expands while it does, so use less than feels right, clamp it, and expect to trim foam off afterward. Wear gloves; it does not come off skin.
Gorilla also sells a yellow wood glue that behaves like Titebond rather than like the polyurethane. Read the bottle, not the brand.
The joints we use
Unit 2 deliberately varies the joint type across teams, so you'll see several of these in the room at once.
| Joint | How it works | Good for | Watch out for |
|---|---|---|---|
| Butt joint | Two square edges meeting, held by screws or glue | Fast, low-load assemblies | Weakest option; end-grain glue barely holds |
| Rabbet | A step cut along one edge, the other part sits in it | Box corners, back panels | Needs accurate depth or the corner shifts |
| Dado | A slot across one part, the other slides in | Shelves in a case | Slot must match measured thickness, not nominal |
| Finger / box joint | Interlocking square fingers | Strong CNC-cut box corners | Inside corners need relief — see Designing for the CNC |
| Dovetail | Angled interlocking fingers that resist pulling apart | Drawers, anything under tension | Least forgiving of dimension errors |
| Mortise and tenon | A peg on one part into a socket in the other | Frames, legs, structural joints | Requires careful layout on both parts |
Every one of these depends on the slot matching the tab. Get the number from Tolerance and Fit and from a test cut, not from the nominal thickness printed on the sheet.
Fastening printed parts to wood
This comes up constantly once your project mixes 3D-printed parts with CNC-cut structure.
- Screws straight into plastic work for light loads, but the threads chew out after a few removals. Fine for something assembled once.
- Glue works when the joint never has to come apart — polyurethane glue for plastic onto wood, per the glue section above.
- Bolt through, nut behind is the simplest strong option when you can reach both sides — model a hex pocket to capture the nut and it becomes a one-wrench job.
- Design the fastener in from the start. A hole added after the fact usually lands somewhere structurally unfortunate. If your project requires real fasteners, they belong in the CAD model.