Joint Clearance

Joint clearance is the intentional or actual gap between mating parts at a joint, used to permit assembly, compensate for tool and material variation, and control fit quality in CNC joinery, millwork, and mechanical assemblies. In CNC woodworking, clearance is built into the CAD/CAM model or toolpath so parts mate without crushing fibers or binding; tight fits often require slight per-side increases depending on machine, bit, and material.

On the shop floor, joint clearance is set by combining CAD offsets, CAM tool compensation, tool diameter, cutter deflection, hold-down conditions, and stock variability so finished parts assemble predictably after machining. For CNC sheet goods and millwork, clearance is tuned through test cuts because plywood thickness, veneer compression, adhesive squeeze-out, and humidity can make a nominal fit too tight even when the CAM is dimensionally correct. In profile and pocket work, clearance is tied to cutter access: dogbone or T-bone reliefs are added where the router bit cannot cut an inside corner fully, allowing the mating tab to seat without corner interference. In precision mechanical fit contexts, joint clearance is managed as a tolerance range rather than a single number; a clearance fit always leaves a gap and allows free movement, with recommended values depending on diameter, material, and function.

• ⚠️Nominal fit ignores real wood movement: Parts cut to the drawing still bind after machining because plywood thickness varies, solid wood moves with moisture, and glue swells the joint line, so clearance must be experimentally derived.
• ⚠️Tool radius not relieved in corners: Inside corners of slots and tab pockets retain an uncut fillet from the end mill, so a square mating part bottoms out and feels too tight even when slot width is correct.
• ⚠️Clearance added in the wrong place: If it lives only in CAD and is not matched in CAM stock-to-leave, roughing passes remove too much or too little material, causing loose joints, split edges, or gaps.