A plunge router is a woodworking machine that spins a cutting bit at high speed while allowing the bit to move straight down into the workpiece. This makes it useful for grooves, mortises, pockets, inlays, hinge recesses, and stopped cuts that do not begin at an edge. Understanding the parts of the router helps a student use it accurately and safely.
The key idea is controlled motion, with rotation cutting the wood and the plunge mechanism setting how deep the cut goes.
Key Facts
- Cutting speed at the bit edge depends on diameter and rotation rate: v = πdN, where d is bit diameter and N is rotations per second.
- Plunge depth is set by the depth stop rod and turret stop before the cut begins.
- A shallow pass is safer and cleaner than one deep pass because it reduces motor load, heat, and bit deflection.
- Feed direction matters: for most edge routing, feed the router against the bit rotation to maintain control.
- Power relates to torque and angular speed: P = τω, where P is power, τ is torque, and ω is angular velocity.
- Always unplug the router before changing bits, adjusting the collet, or setting the depth stop.
Vocabulary
- Plunge router
- A router with a spring-loaded base that lets the spinning bit move vertically into and out of the workpiece.
- Collet
- The clamping part that grips the shank of the router bit and holds it centered on the motor shaft.
- Depth stop rod
- An adjustable rod that limits how far the router can plunge downward during a cut.
- Turret stop
- A stepped rotating stop that allows several preset plunge depths for making cuts in multiple passes.
- Feed rate
- The speed at which the router is moved through the wood during cutting.
Common Mistakes to Avoid
- Taking the full depth in one pass is wrong because it can burn the wood, overload the motor, break the bit, or pull the tool off line.
- Leaving the bit loosely clamped in the collet is wrong because the bit can slip, vibrate, or eject during high speed rotation.
- Feeding the router in the wrong direction is wrong because the bit can climb along the workpiece and reduce control.
- Plunging before the base is flat on the workpiece is wrong because the bit can enter at an angle and damage both the cut and the tool.
Practice Questions
- 1 A router bit has a diameter of 12 mm and spins at 20,000 rpm. What is the approximate cutting speed at the outer edge of the bit in meters per second?
- 2 A mortise must be cut 18 mm deep. If each pass removes 6 mm, how many plunge passes are needed, and what depth should the stop be set to for each pass?
- 3 A student wants to cut a clean stopped groove in the middle of a board. Explain why a plunge router is better suited than a fixed-base router for starting this cut safely and accurately.