SB CG1/Cutting tools

GCode programming


In the context of machining, a cutting tool or cutter is any tool that is used to remove material from the workpiece by means of shear deformation.

Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, planing and similar operations, and remove material by means of one cutting edge.

Milling and drilling tools are often multipoint tools. Grinding tools are also multipoint tools. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip.

Cutting tools must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the workpiece without the rest of the tool dragging on the workpiece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life, all of the above must be optimized, plus the speeds and feeds at which the tool is run.


End mill nose types.png
  • Flat nose mills are used for milling 2D contours and pockets.
  • Ball nose mills are used for 3D milling.
  • Bull nose end mills have a radius corner. They are used to create a fillet on the bottom of a wall. Because they are sturdier than an end mill they are also sometimes used for roughing operations.
  • Chamfer mills have an angled nose used to create a chamfer or to de-burr parts.


Face mill.png
  • A face mill has cutting inserts that are replaced when worn.
  • They are rigid, may have up to eight or more cutting edges, and can remove material quickly.
  • They are often used for the first machining operation to quickly create a flat finished face on the part.

Corner Radius Tool

Corner rounding tool.png
  • Corner radius (also called Corner Round) tools are used to place a fillet on the outside corner of a part.

Slot Mill / Slotting Saw

  • Slot mills include side milling cutters, slitting saws, and Woodruff keyset cutters.
  • Slitting saws and side milling cutters are installed on a special arbor.
  • Woodruff cutters are single piece tools used for creating slots and undercuts that can be held in a standard tool holder.

Center-Spot Drills

Center drill.png

Center (spotting) drills are short and very rigid drills used to create a conic on the face of the part. Because they come to a sharp point and resist bending, they locate the hole precisely. The conic helps prevent the subsequent drill from wobbling and ensure the drill is located precisely and drills straight down.

Countersink drills are used to create the conical face for a machine screw. Combined spotting-countersinks are used to create a screw clearance hole and countersink in one operation.

There are many different sizes and tip angles of center, countersink, and combined drills. Be sure the tip angle of the countersink matches the included angle of the machine screw, and that the drill diameter is greater than the screw head diameter.

Twist Drill

  • Twist drills are available in many diameters and lengths.
  • Usually made of high speed steel, carbide, or cobalt, they may also be coated with titanium nitride (TiN) for longer life.
  • The tip angle of most twist drills is 118 degrees.


  • Cutting taps form threads by shearing material away. Form taps (roll taps) form the thread by forming the metal to shape.
  • Form taps produce no chips and are used for soft materials including aluminum, copper, brass and plastics.
  • Bottoming taps are used to tap blind holes. Spiral point taps push the chip ahead and out the bottom of a through hole.
  • Taps require a hole drilled to the correct size to ensure the thread is formed properly


  • Use reamers to create holes of precise shape and excellent surface finish.
  • Reamed holes are usually accurate within .0005 mm diameter. For example, a reamer is used for holes used for ground pins and bushings.
  • Reamers require a specific size hole be drilled before use.
  • Cutting speeds and feeds are also important. Remove too little or too much material and the hole will not be the correct size.


  • A counterbore looks similar to a end mill with a pilot in the center. It is used to spot face holes, and the pilot ensures the spot face is centered on the hole.

Counterboring is not necessary when using a CNC machine. Rather, create a spot face using a pocket or circle mill tool path. This saves having to buy and stock counterbore tools and pilots, and the time required to load and set up the counterbore.