Milling Operations

There are many different operations that can be done on the mill and with the proper tooling and setup the possibilities are endless.

Coolant is often used when conducting milling operations. See the full Coolant page for info on coolant usage.

Climb Milling vs Conventional Milling

Climb vs conventional milling depends on which side of the endmill is doing the cutting. In climb milling, the cutter rotates against the feed direction, while in conventional milling, the cutter rotates with the feed direction.

Both are valid methods of material removal, however they each have advantages and disadvantages, therefore it is important to understand which is being done for troubleshooting reasons.

Climb Milling:

The tool enters the cut with a thick chip and gradually reduces chip thickness as it moves through the material.

Benefits: Better surface finish, less vibration, less tool wear, more control over the cutting process.

Considerations: Requires a rigid setup to prevent displacement and poses the potential for the cutter to pull into the workpiece if not properly controlled.

Conventional Milling:

The tool enters the cut with a thin chip and gradually increases chip thickness as it moves through the material.

Benefits: Easier to control on machines with backlash, can be beneficial for roughing operations.

Considerations: Can lead to more vibration and may result in a rougher surface finish. Can lead to more tool wear.

Face Milling

Face milling creates a flat surface perpendicular to the spindle axis—typically the top of a part.

How It Works:

A flat-bottomed cutter (often a large endmill or a shell mill) spins while the table feeds the part beneath it. The wide cutting area allows large surfaces to be machined quickly.

Tips:

• Use a wide cutter for even finish across the part
• Keep the Z-depth constant and use the X or Y axis to traverse
• Climb milling may give a better surface finish but requires a rigid setup

Common Use Cases:

• Squaring up stock
• Removing scale or high spots
• Creating reference surfaces

In this drawing, a_r refers to the depth of cut and a_s refers to tool engagement length.

Side Milling

Side milling is used to machine vertical faces along the edges of the part, or to clean up the sides after rough cutting.

How It Works:

The cutting tool (typically an endmill) removes material from the side of the workpiece as it passes by, using the periphery of the tool.

Tips:

• Always check tool stick-out: the tool should be long enough, but not excessive
• Use a slow, steady feed rate to reduce chatter
• Lock unused axes for a rigid cut
• Leave a small finishing pass for better surface quality

Common Use Cases:

• Squaring sides of a block
• Cleaning up saw-cut or rough edges
• Cutting shoulders or steps into a part

Drilling (on the Mill)

The mill can effectively be used as larger drill presses that provide more accurate measurements for hole location and depth. See the complete Drilling page for info on various types of drilling and drill bits.

How It Works:

A drill bit is held in a drill chuck or collet in the spindle. The quill is used to plunge the bit into the part.

Tips:

• Always center-drill first for accuracy
• Use the DRO to position holes precisely
• Start with slower spindle speeds for larger bits
• Clear chips often to avoid binding
• Peck drilling (lifting the drill periodically) helps chip evacuation

Common Use Cases:

• Accurate bolt patterns
• Pilot holes for tapping
• Starter holes for reaming or boring

Boring

Boring is the process of enlarging a hole with a single-point cutting tool to achieve a precise diameter, roundness, and surface finish. It’s typically used when a drilled hole is close to size but needs to be brought to an exact dimension—or when a hole needs to be aligned concentrically to other features.

Unlike drilling, which is limited by the bit size and can leave rough or oversized holes, boring gives the machinist fine control over diameter and finish.

Tools Used for Boring

• Boring Head - A precision-adjustable tool that mounts in the spindle. The head holds a small boring bar off-center and allows you to dial in cut diameter via a fine adjustment screw.
• Boring Bar - A small, rigid bar with a single cutting tip—often carbide or HSS—that removes material as it swings in a circular path inside the hole.
• Drill or Center Drill (Pre-Step) - Used to create a starter hole before boring. Typically, you’ll drill a hole slightly under the final size and then use the boring head to finish it.

When to Use Boring

• You need a hole with precise diameter, especially for bearings or dowel fits
• You want a better surface finish than a drill can produce
• You need to align a hole perfectly relative to other features (e.g. from a pre-bored setup)
• You’re correcting an out-of-round or misaligned hole
• You’re enlarging a casting hole or rough bore that’s uneven

Shape Cutting with Form Tools

Form cutting is the process of using a cutter with a pre-machined profile to impart that shape directly into the workpiece. Rather than generating a curve through toolpaths (like in 3D contouring), the cutter itself is shaped to create the desired geometry—like a rounded edge or fillet.

This is often used to:

• Add a radius to a part edge
• Cut chamfers
• Machine decorative or ergonomic features
• Match mating surfaces
• Prep a part for welding or assembly

Fly cutting

Fly cutting is a technique used to produce a very flat and smooth surface using a single-point cutting tool mounted in a fly cutter body. It’s ideal for creating flat reference surfaces on large parts, cleaning up castings, or squaring up stock that's too wide for standard endmills.

A fly cutter is a tool holder that spins a single cutting bit around the center of the spindle. The cutting edge sweeps across the workpiece, much like a lathe tool on a rotating part—but in reverse. Most fly cutters use a small HSS tool bit that can be ground to a specific shape or radius depending on the finish desired.

When to Use Fly cutting

• Flattening large surfaces wider than your largest endmill
• Improving surface finish on aluminum, brass, or mild steel
• Creating reference faces before precision machining
• Squaring up rough stock, especially if it came from a bandsaw or casting

It’s not a fast operation, but it delivers excellent flatness and surface quality—especially on manual mills.

Setup and Tips

• Mount securely: Insert the fly cutter in an R8 collet or endmill holder. Ensure it spins true with no visible wobble.
• Set tool height: Adjust the cutting bit so it’s exactly on the centerline of the spindle. Too high or low can cause uneven surfaces.
• Balance matters: The cutter sweeps a large arc, so imbalance can cause vibration. Keep the cutting edge close to the center and minimize tool stick-out.
• Use low RPMs: Fly cutters have large effective diameters, so keep spindle speed low—usually 300–600 RPM depending on size and material.

• Set the depth of cut shallow—around 0.005" to 0.010" per pass is typical.
• Use slow, steady feed. Too fast a feed or deep a cut will cause chatter or poor finish.
• Lock all unused axes, especially the quill and Y-axis.
• For best results, make multiple light passes rather than one aggressive cut.