CNC Machining Glossary

An axis is a direction a CNC machine can move. Most machines have 3 axes: left-right (X), front-back (Y), and up-down (Z). Advanced machines add 4th and 5th axes for rotation.

Anodizing is a process that adds a hard coating to aluminum parts. It protects against scratches and corrosion. You can also add color during anodizing.

An arbor is a shaft that holds a cutting tool in the machine. It connects the tool to the spindle so it can spin and cut.

An ATC swaps cutting tools during a job without stopping the machine. This lets the machine use many tools in one setup, which saves time.

Backlash is the tiny gap between gears or screws in a machine. When gears change direction, this gap causes a small error. Less backlash means more accurate parts.

A ball end mill has a rounded tip shaped like a ball. It cuts smooth, curved surfaces and 3D shapes. It is common in mold making.

To bore means to enlarge a hole that already exists. Boring makes holes very round and accurate. The result is also called a bore.

A burr is a tiny, sharp edge left on a part after cutting. Burrs must be removed so parts fit together safely. Removing them is called deburring.

Brinell hardness measures how hard a metal is. A steel ball is pressed into the surface. The dent size tells you the hardness number. Higher numbers mean harder metal.

CAD stands for Computer-Aided Design. Engineers use CAD software to draw 3D models of parts on a computer. The model tells the machine what to make.

CAM stands for Computer-Aided Manufacturing. CAM software turns a CAD model into instructions the machine can follow. It plans the tool paths and cutting speeds.

A chamfer is a small angled cut on the edge of a part. It removes sharp corners. Chamfers make parts safer to handle and easier to assemble.

A chuck is a clamp that holds the workpiece or tool in place. On a lathe, the chuck grips the spinning part. Chucks can have 3 or 4 jaws.

Climb milling means the cutter spins in the same direction as the feed. It makes a cleaner cut and puts less stress on the tool. Most CNC mills use climb milling.

CNC stands for Computer Numerical Control. It means a computer tells the machine exactly where to move and how fast to cut. CNC machines make parts with very high accuracy.

A collet is a sleeve that squeezes tight around a tool to hold it. It grips the tool evenly on all sides. Collets provide very accurate tool holding.

Coolant is the liquid sprayed on the tool and part during cutting. It keeps things cool, washes away chips, and helps the tool last longer.

A countersink is a cone-shaped hole at the top of a drilled hole. It lets a flat-head screw sit flush with the surface.

A counterbore is a flat-bottomed hole cut into a larger hole. It lets a bolt head sit below the surface. The bottom is flat, unlike a countersink.

Cutting speed is how fast the tool edge moves past the material. It is measured in surface feet per minute (SFM). The right speed depends on the material and tool type.

A datum is a reference point or surface on a part. All measurements start from the datum. It helps the machinist set up the part the same way every time.

Deburring means removing the small, sharp edges left after cutting metal. It makes parts smooth and safe. You can deburr by hand, with a tool, or with a tumbler.

Depth of cut is how deep the tool goes into the material in one pass. A deeper cut removes more material but puts more force on the tool.

DFM stands for Design for Manufacturability. It means designing parts so they are easy and affordable to make. Good DFM avoids features that are hard to machine.

A drill press is a machine that drills straight holes. It has a spinning drill bit that moves up and down. Drill presses make more accurate holes than hand drills.

A dwell is a short pause during machining. The tool stays in place and keeps spinning. This can improve surface finish at the bottom of a hole.

Dry machining means cutting without coolant or lubricant. Some materials and tools work well dry. It saves money and reduces cleanup.

An edge finder is a tool that locates the exact edge of a workpiece. The machinist uses it to set the zero point before cutting starts.

An end mill is a cutting tool used in milling machines. It has sharp edges called flutes that cut on the sides and bottom. End mills come in many shapes and sizes.

EDM stands for Electrical Discharge Machining. It uses tiny electric sparks to remove metal. EDM can cut very hard materials and make shapes that regular tools cannot.

Face milling cuts a flat surface across the top of a workpiece. A wide cutter shaves off material evenly. It is one of the most common milling operations.

Feed rate is how fast the cutting tool moves through the material. It is measured in inches per minute (IPM) or millimeters per minute. The right feed rate depends on the tool and material.

A fillet is a rounded inside corner on a part. End mills naturally leave fillets because the tool tip is round. Fillets also make parts stronger at corners.

A fixture is a custom holder that keeps a part locked in place during machining. Good fixtures let you machine many parts the same way, fast and accurate.

A flute is a groove cut into a milling tool. Flutes create the sharp cutting edges. More flutes give a smoother finish. Fewer flutes clear chips faster.

A fly cutter uses a single cutting edge on a spinning arm. It shaves wide, flat surfaces very smooth. Fly cutters are great for making mirror-like finishes.

G-code is the language CNC machines understand. Each line tells the machine to move, cut, or change speed. CAM software writes most G-code automatically.

Gang tooling lines up many tools on one holder. The machine slides to each tool instead of swapping. This speeds up turning jobs with many operations.

GD&T stands for Geometric Dimensioning and Tolerancing. It uses special symbols on drawings to say how flat, round, or straight a feature must be. It goes beyond basic measurements.

A gantry is a bridge-shaped frame that holds the spindle. The spindle rides along the gantry to reach different areas of the workpiece. Gantry machines handle very large parts.

Grinding uses a spinning wheel with tiny abrasive grains to remove small amounts of material. It makes surfaces very smooth and parts very precise.

Hardness measures how well a material resists dents and scratches. Harder metals are tougher to machine but last longer. Common scales include Brinell, Rockwell, and Vickers.

Heat treatment heats and cools metal to change its properties. It can make metal harder, softer, or more flexible. This is often done after machining.

The helix angle is the spiral angle of the flutes on an end mill. A higher angle gives a smoother cut. Most standard end mills have a 30-degree helix.

High-speed machining (HSM) runs the spindle and feed faster than normal. It takes lighter cuts at higher speeds. HSM reduces cycle time and can improve surface finish.

Honing uses fine abrasive stones to smooth the inside of a cylinder. It creates a precise, round bore with a very fine surface finish.

Indexing means rotating a workpiece to a set angle. The machine locks it in place, then cuts. This lets you machine features at exact positions around the part.

An insert is a replaceable cutting tip that bolts onto a tool holder. When the edge gets dull, you swap just the insert. This costs less than replacing the whole tool.

Interpolation is how a CNC machine moves between two points. Linear interpolation moves in a straight line. Circular interpolation moves in an arc. The machine blends many small moves into smooth shapes.

Jaws are the gripping fingers inside a chuck. They open and close to hold the workpiece. Hard jaws grip round stock. Soft jaws can be shaped to hold odd parts.

A jig is a device that holds a part and guides the cutting tool. It tells the tool exactly where to cut. Jigs help make many identical parts quickly.

Kerf is the width of material removed by a cutting tool. A saw blade or laser has a kerf. You must account for kerf width when planning cuts.

Knurling presses a diamond or straight-line pattern into a round surface. The textured grip makes parts easier to turn by hand. It is done on a lathe.

A lathe spins the workpiece while a fixed tool cuts it. It makes round parts like shafts, pins, and bushings. CNC lathes are controlled by computer.

Live tooling adds spinning tools to a lathe. This lets the lathe drill holes and mill flats without moving the part to another machine. It saves time and improves accuracy.

Lot size is the number of parts made in one production run. A small lot might be 10 parts. A large lot could be 5,000 or more. Bigger lots usually cost less per part.

M-codes control machine functions like turning the spindle on, starting coolant, or changing tools. They work alongside G-codes to run the full machining program.

Machinability rates how easy a material is to cut. Aluminum has high machinability. Titanium has low machinability. Easier-to-cut metals cost less to machine.

A mandrel is a bar inserted into a hollow part to support it during machining. It keeps thin-walled tubes from bending or vibrating while the tool cuts.

A micrometer is a measuring tool that reads to 0.0001 inches. It clamps around a part to measure thickness or diameter. Machinists use micrometers to check part sizes.

Milling uses a spinning cutter to remove material from a fixed workpiece. It can make flat surfaces, slots, pockets, and complex 3D shapes. CNC milling is one of the most common machining processes.

NC stands for Numerical Control. It is the older version of CNC. NC machines read instructions from punch tape. CNC replaced NC by using computers instead of tape.

Nesting arranges parts on a sheet of material to waste as little as possible. Good nesting fits more parts from one sheet. This saves money on raw material.

An offset is a value that adjusts the tool or work position. Tool length offset tells the machine how long the tool is. Work offset sets where the part is on the table.

Overcut happens when the tool removes more material than planned. In EDM, overcut is the gap between the electrode and the workpiece. Machinists plan for it to keep parts accurate.

A pallet is a movable platform that holds a workpiece. The machine loads one pallet while the operator sets up the next. This keeps the machine running with less downtime.

Peck drilling drills a little, pulls out, then drills deeper. Each peck clears chips from the hole. This prevents the drill from breaking in deep holes.

Plunge milling pushes the tool straight down into the material. It removes stock fast in deep pockets. The cutting force goes along the spindle, which is very stable.

A post processor converts CAM output into G-code that a specific machine can read. Each machine brand needs its own post processor. It is the last step before running the program.

Probing uses a touch probe to measure a part on the machine. The probe touches the surface and records the position. It sets offsets and checks dimensions without removing the part.

A quill is the sliding sleeve in a drill press or milling machine that holds the spindle. You move the quill up and down to feed the tool into the work.

Rake angle is the tilt of the cutting edge on a tool. A positive rake slices easily but the edge is weaker. A negative rake is stronger but needs more force to cut.

Rapid traverse is the fastest move a CNC machine can make. The tool moves quickly between cuts without touching the material. This saves time between operations.

A reamer is a tool that slightly enlarges a drilled hole to make it very round and smooth. It removes only a tiny amount of material for a precise fit.

Roughing is the first pass that removes most of the material fast. It does not need a smooth finish. A finishing pass comes after to make the surface smooth and accurate.

Runout measures how much a spinning tool or part wobbles. Less runout means the tool spins truer. High runout causes uneven cuts and shorter tool life.

RPM stands for Revolutions Per Minute. It tells how many times the spindle or workpiece spins each minute. The right RPM depends on the tool size and cutting speed.

SFM stands for Surface Feet per Minute. It measures how fast the tool edge moves past the material. SFM helps you pick the right RPM for each tool and material combination.

Shoulder milling cuts a flat wall and a flat floor at the same time. It creates a square step or ledge on the part. The tool cuts on both the side and the bottom.

Slotting cuts a narrow channel or groove into a part. The tool plunges into the material and moves along a line. Slots hold keys, guides, or other parts.

The spindle is the part of the machine that spins. On a mill, the spindle holds and spins the tool. On a lathe, the spindle holds and spins the workpiece.

Step-over is how far the tool moves sideways between each pass. A smaller step-over gives a smoother finish but takes more passes. It is usually set as a percentage of the tool width.

Surface finish describes how smooth a machined surface is. It is measured in micro-inches (Ra). A lower Ra number means a smoother surface. Finish depends on tool, speed, and step-over.

Swarf is the small chips and shavings of metal produced during cutting. Another name for swarf is chips. Coolant helps flush swarf away from the cut.

Tapping cuts threads inside a hole so a screw or bolt can thread in. A tap is the tool that does this. CNC machines can tap holes automatically with precise depth control.

Thread milling uses a milling cutter to carve threads in a helical path. It can make threads in different sizes with one tool. Thread milling works well for large or hard-to-tap holes.

Tolerance is the allowed amount of variation in a part's size. A tight tolerance like +/- 0.001 inches means the part must be very exact. Tighter tolerances cost more to achieve.

A tool path is the route the cutting tool follows to shape the part. CAM software generates the tool path from a 3D model. It includes where to cut, how deep, and how fast.

A trunnion is a tilting table on a CNC mill. It adds a 4th or 5th axis by rotating the part. This lets the machine reach more angles without re-fixturing.

Turning spins the workpiece while a fixed tool removes material. It makes round parts like shafts, tubes, and cones. Turning is done on a lathe.

An undercut is a feature where material is removed under a lip or ledge. Standard tools cannot always reach undercuts. Special tools or extra setups may be needed.

A vise clamps the workpiece to the machine table using two jaws. You tighten the handle to grip the part firmly. Vises are the most common workholding method in milling.

Vickers hardness tests push a diamond-shaped point into the surface. The dent size gives the hardness number. This test works on very thin or very hard materials.

Workholding is the overall method of holding a part during machining. Vises, chucks, fixtures, and clamps are all workholding devices. Good workholding keeps parts still and accurate.

A work offset tells the machine where the part sits on the table. It sets the zero point for that job. Multiple work offsets let you machine several parts in one setup.

A worm gear has a screw-shaped gear that meshes with a toothed wheel. It changes rotation direction and reduces speed. Worm gears are found in rotary tables and indexing heads.

The X-axis is the left-right direction on a CNC machine. On a mill, the table moves left and right along the X-axis. It is one of three main movement directions.

The Y-axis is the front-to-back direction on a CNC machine. On a mill, the table moves toward and away from the operator along the Y-axis.

The Z-axis is the up-and-down direction on a CNC machine. On a mill, the spindle moves up and down along the Z-axis to set cutting depth.

The zero point is where X, Y, and Z all equal zero on the machine. All tool movements are measured from this point. Setting the zero point correctly is one of the most important setup steps.