Machining, Joinery and Assembly
This domain tests joinery selection, machining tolerance and the assembly sequence - the point where good parts either become a square, tight cabinet or a pile of scrap. Questions ask which joint suits a load or a location, how much material to leave for machining, and what went wrong at glue-up.
Choosing and cutting joints
- Mortise and tenon for structural frames; a haunched tenon resists twisting in a door stile.
- Dovetails for drawer boxes and carcass corners in fine work; dowels and biscuits for alignment and moderate strength.
- Dado, rabbet and groove for shelving and panel capture; cope-and-stick for raised-panel door frames.
- Loose tenons and pocket screws are fast and repeatable, but respect the load path and grain direction.
Machining practice
- Mill stock oversize and dress to final dimension; leave 1 to 2 mm for cleanup when a second operation will true the face.
- Cut test joints on scrap from the same setup - a 0.2 mm change in cutter height changes the fit.
- Check machine square, not just the part: a table saw that is out of square produces consistent, repeatable error.
Assembly and clamping
- Dry fit everything, including hardware clearances, before glue.
- Glue spread should be thin and even on both faces; too little starves the joint, too much gets squeezed out and starves it anyway.
- PVA open time is around 5 to 10 minutes; clamp time about 30 to 60 minutes; full cure around 24 hours.
- Clamp pressure should be firm and even - enough to close the joint with a thin bead of squeeze-out, not enough to crush end grain.
- Check diagonals after clamping, before the glue sets.
Worked example
A face frame comes out of clamps 4 mm out of square across the diagonals. Reasoning: first check the carcass and the clamping bars - uneven clamp pressure pulls a frame into a parallelogram. Second, verify the parts were cut square and the same length. Third, check whether the assembly sat on an uneven bench. The fix is to clamp across the long diagonal to correct, confirm both diagonals are within about 1 mm, then re-check with a square on the inside corner before the glue cures. Trimming after cure would just hide the cause.
Traps that cost marks
- Over-clamping and starving the glue line.
- Gluing a solid panel into a frame with no room for movement.
- Skipping the dry fit, then discovering a drawer will not clear a hinge.
- Machining to final size in one pass without checking against a test cut.