Clearance Fit

Clearance fit is a shaft-to-hole fit where the hole diameter is always larger than the shaft diameter, guaranteeing positive clearance across all tolerance combinations. This fit allows free movement, sliding, rotation, or easy assembly, and accommodates thermal expansion, contamination, and disassembly needs. It is the opposite of interference fit and is specified when motion or frequent assembly is required.

On a CNC mill or router, clearance fit is selected by choosing a hole/bore tolerance that remains larger than the mating feature after accounting for tool deflection, cutter wear, material movement, and process variation. In practice, this fit is used for slip joints, guide pins, shafts, bearing carriers, fastener clearance holes, and removable fixtures where parts must slide or pass through without force. In millwork and edgebanding, clearance is deliberately added to compensate for panel thickness variation, adhesive film thickness, seasonal wood movement, and machining tolerance stack-up—because parts cut to nominal size often fail to assemble cleanly without extra gap. The fit is not merely a gap but a controlled allowance: the minimum hole and maximum shaft still assemble, while the maximum hole and minimum shaft do not become so loose that alignment, vibration, or cosmetic reveal quality suffers. Common clearance-fit families include close clearance, locational clearance, sliding, close running, free running, and loose running, spanning applications from precision alignment to dirt-tolerant pivots.

• ⚠️Tool wear closes the fit up: if the program is tuned to nominal dimensions and the cutter wears undersize or the bore finishes small, the intended clearance disappears and the part starts to bind, especially in long production runs or hard materials.
• ⚠️Ignoring process variation creates either drag or slop: if thermal expansion, chip load deflection, clamp distortion, MDF swell, or wood movement is not included in the allowance, the joint may be too tight to assemble or too loose to control position.
• ⚠️Assuming 'clearance hole' means any oversize hole: a hole that is merely larger than the fastener is not automatically a good fit; if the clearance is excessive, the fastener can shift under vibration, alignment can drift, and clamped assemblies can lose positional accuracy.