Milling machines are among the most commonly used machine tools in modern manufacturing. You’ll find them in everything from major assembly lines to small tool-and-die shops, and just about anywhere in between. Just about every industry uses milling machines, from mini-mills in high-end scientific labs to the automotive industry.
Milling machines are popular with many manufacturers and engineers, as they help to produce parts that are more complex than the average 3D printer can handle. In this guide, we will give you some background on milling machines including what they are used for, how they work, and what features to look out for when purchasing one. You’ll have everything you need to know to purchase your own milling machine with confidence.
What is Milling Machine?
A milling machine is a device that rotates a circular tool that has a number of cutting edges symmetrically arranged about its axis and the workpiece is commonly held in a vise or similar device clamped to a table that can move in three perpendicular directions.
Milling Machines are used for machining solid materials, including metal, plastic, and wood, and are commonly used to machine irregular and flat surfaces. The cutter is designed to rotate during the operation as opposed to a lathe, where the part itself rotates during the cutting operation.
Milling machines are powered machine tools that are designed to mill or carve material. Mills use a variety of cutting tools, including rotating blades, drills, and even abrasives.
The best mills feature high-quality cast iron construction, variable speed engines, power feeds, and cutting tools that move along the x- and y-axis. Milling machines are used in a variety of roles from woodworking to metalworking.
Milling machines commonly have self-contained electric drive motors, coolant systems, digital readouts, variable spindle speeds, and power-operated table feeds. They can also be used to drill, bore, cut gears, and produce slots and pockets.
A milling machine is designed to hold material securely in a vise or otherwise secured to the bed of the mill. The cutting tool itself typically has either horizontal or vertical movement, which in turn gives its name to the two basic kinds of milling machines; horizontal and vertical milling machines.
Vertical mills use a rotating cutting tool that most closely resembles a drilling machine or drill press. The drill chuck is mounted on a gantry above the bed of the mill and is lowered into the workpiece.
The cutting tool is generally a single-pointed milling cutter. Depending on the specifications of the particular mill, milling machines have a tool head speed of anywhere from 500 to 50,000 RPM.
A horizontal milling machine functions similarly to a vertical mill with the exception that it uses a rotating table instead of a gantry and its main cutter is generally three- or four-pointed. The cutting speed for these mills also varies according to specifications but can be as fast as 20,000 RPM.
What kind of milling machine do you need?
There are a number of combo machine tools that combine elements of a milling machine with other common tools. Mini mills certainly aren’t the only variation on the milling machine theme.
Mill drills closely resemble drill presses or simplified vertical mills. Specialized grinding machines or grinders take some elements from the horizontal mill and combine them with a step-down process to slowly remove material from a workpiece, creating a flat surface.
When it comes to “proper” milling machines, there are still a number of choices. Knee mills are smaller milling machines, often designed as benchtop mills, that is equally at home in the home workshop or industrial machine shop.
CNC milling machines are the top-end option, providing a high precision solution to parts manufacturers.
Parts of Milling Machine
Main Parts of the Milling Machine:
- Column and Base.
- Saddle and Swivel Table.
- Power Feed mechanism.
- Over Arm / Overhanging Arm.
- Arbor Support.
Let’s go through each one of them:
1. Column and Base
The column is another foundation part of the milling machine. It is a mountain vertically on the base. It supports the knee, table, etc. Work as housing for all the other driving members. It is a hollow member consisting of driving gear and sometimes a motor for the axle and table. The column has an oil repository and pumps to lubricate the axles.
The knee is the first moving part of the milling machine. The saddle and table support casting. The gearing device is included within the knee. The knee is fastened to the pillar by Dowell’s methods.
It is maintained and improved by a vertical positioning screw, also recognized as an elevating screw. Elevating screw is used to adjust the knee up and down by moving the lever up or down with the help of a hand or power feed.
3. Saddle and Swivel Table
The saddle is at the knee and supports the table. The saddle slides on the horizontal dovetail on the knee and the dovetail is parallel to the axis of the axis. A swivel table is attached to the saddle which rotates horizontally in both directions.
4. Power Feed mechanism
The power feed mechanism is in the knee. The power feed mechanism is used to control longitudinal, transverse, and vertical feeds. For the desired rate of feed on the machine, the feed selection lever is positioned to point at the feed selection plates.
For any column milling machine and universal knee, feed is obtained by turning on the speed selection handle until the rate of feed selection is shown on the dial.
In almost every milling machine, there is a quick-moving lever, which is applied when a temporary boost in longitudinal, transverse, or vertical feed speed is required. This lever is applied when the operator is arranging or positioning the work.
The table is a rectangular casting that is present at the top of the saddle. The table is used to hold a task or for task holding devices. There are several T-slots to hold the work and hold the equipment. It can be performed by hand or by power.
To move the table by hand, turn and rotate the longitudinal arm crank. For gait, it feeds the control lever by force, attached, and longitudinal direction.
It is placed between the table and the knee and acts as an intermediate part between them. This column can move transversely on the face. It slides on guideways that are located at the knee that are perpendicular to the face of the column. Its main function is to move the workpiece in a horizontal direction. It is also made of cast iron.
7. Over Arm/Overhanging Arm
It is an overhang on the surface of the column and the other end supports the arbor. It can be a single casting and slide that is at the top of the column in a dowel manner. It is located above the column on a horizontal milling machine. It is made of cast iron.
8. Arbor Support
The arbor support is cast with a bearing that supports the outer end of the arbor. It also helps align the outer end of the arbor with the axle. Arbor support prevents the springing of the outer end of the arbor in a cutting operation.
Typically, two types of arbor support are used in milling machines. The first one has a small diameter bearing hole with a maximum diameter of 1 inch. The second has a large diameter hole of up to 23/4 inches.
Rams serve as the overhanding arm in a vertical milling machine. One end of the ram is placed on top of the pillar and the milling head is attached to the other. One end of the arm is attached to the pillar and the other end is attached to the milling head.
Setup For Milling Operation
The success of any milling operation depends, before setting up a job, be sure that the to a great extent, upon judgment in setting up the job, workpiece, the table, the taper in the spindle, selecting the proper milling cutter, and holding the cutter by the best means under the circumstances.
Some fundamental practices have been proved by experience to be necessary for and the arbor or cutter shank are all clean and good results on all jobs. Some of these practices are mentioned below:
- Before setting up a job, be sure that the workpiece, table, the taper in the spindle, and the arbor or cutter shank are free from chips, nicks, or burrs.
- Do not select a milling cutter of larger diameter than is necessary.
- Check the machine to see if it is in good running order and properly lubricated, and that it moves freely, but not too freely in all directions.
- Consider direction of rotation. Many cutters can be reversed on the arbor, so be sure you know whether the spindle is to rotate clockwise or counterclockwise.
- Feed the workpiece in a direction opposite the rotation of the milling cutter (conventional milling).
- Do not change feeds or speeds while the milling machine is in operation.
- When using clamps to secure a workpiece, be sure that they are tight and that the piece is held so it will not spring or vibrate under cut.
- Use a recommended cutting oil liberally.
- Use good judgment and common sense in planning every job, and profit from previous mistakes.
- Set up every job as close to the milling machine spindle as circumstances will permit.
Different Milling Machine Operations
A milling machine is a machine tool that cuts metal as the workpiece is fed against a rotating multipoint cutter. The milling cutter rotates at a very high speed because of the multiple cutting edges, it cuts the metal at a very fast rate. This machine can also hold single or multiple cutters at the same time.
There are various milling machine operations used for different kinds of jobs.
1. Face Milling
This makes the flat surface at the face of the workpiece. Face milling is done on the surface of the workpiece which is placed perpendicular to the axis of the cutter. This operation is done performed by a face milling cutter mounted on a stub arbor.
Face milling is the simplest milling machine operation. This operation is performed by a face milling cutter rotated about an axis perpendicular to the work surfaces.
The operation is carried in plain milling, and the cutter is mounted on a stub arbor to design a flat surface. The depth of the cut is adjusted by rotating the cross-feed screw of the table.
2. Side Milling
In this process, the flat vertical surfaces produce at the side of a workpiece. This process is done with a side milling cutter.
Side milling is the operation of producing a flat vertical surface on the side of a workpiece by using a side milling cutter. The depth of cut is set by rotating the vertical feed screw of the table.
3. Plain Milling
For the milling of flat surfaces, the axis of the cutter is kept parallel to the surface being milled. It is also known as surface milling or slab milling. The plain milling cutter is used for plain milling.
Plain milling is the most common type of milling machine operation. Plain milling is performed to produce a plain, flat, horizontal surface parallel to the axis of rotation of a plain milling cutter.
The operation is also known as slab milling. To perform the operation, the work and the cutter are secured properly on the machine. The depth of cut is set by rotating the vertical feed screw of the table. And the machine is started after selecting the right speed and feed.
4. Straddle Milling
In this process, the two-side milling cutter is used to machine two opposite sides of a workpiece. Straddle milling is the operation of producing a flat vertical surface on both sides of a workpiece by using two side milling cutters mounted on the same arbor.
Distance between the two cutters is adjusted by using suitable spacing collars. Straddle milling is commonly used to design a square or hexagonal surfaces.
5. Angular Milling
It is used to mill flat surfaces which are neither parallel nor perpendicular to the axis of the milling cutter. It is also known as angle milling. The single-angle milling cutter is used to perform this operation.
Angular milling is the operation of producing an angular surface on a workpiece other than at right angles of the axis of the milling machine spindle. An angular groove may be single or double angle and may be of varying included angle according to the type and contour of the angular cutter used. One simple example of angular milling is the production of V-blocks.
6. Gang Milling
In this machining process, two or more milling cutters are used together to perform different milling operations simultaneously. The cutters are mounted on the arbor in the gang milling.
Gang milling is the operation of machining several surfaces of a workpiece simultaneously by feeding the table against a number of cutters having the same or different diameters mounted on the arbor of the machine.
The method saves much machining time and is widely used in repetitive work. The cutting speed of a gang of cutters is calculated from the cutter of the largest diameter.
7. Form Milling
This operation is used for machining special contour composed of curves, straight lines, or entirely of curves at the single cut. The convex, concave, and corner rounding milling cutters are used in this operation.
Form milling is the operation of producing irregular contours by using form cutters. The irregular shape may be convex, concave, or of any other shape. After machining, the formed surface is inspected by a template gauge. The cutting rate for form milling is 20% to 30% less than that of plain milling.
8. Profile Milling
It is used to cut a profile on the workpiece.
Profile milling is the operation of reproduction an outline of a template or complex shape of a master dies on a workpiece. Different cutters are used for profile milling. An end mill is one of the widely used milling cutters in profile milling work.
9. End Milling
This process is used to produce a flat surface that can be horizontal, vertical, and at any angle taking the worktable as a reference. The end milling cutters are used in this process.
The end milling is the operation of producing a flat surface that may be vertical, horizontal, or at an angle in reference to the table surface. The cutter used is an end mill. The end milling cutters are also used for the production of slots, grooves, or keyways. A vertical milling machine is more suitable for end milling operation.
10. Saw Milling
The sawmilling is used to produce narrow grooves or slots on the workpiece.
Saw-milling is the operation of producing narrow slots or grooves on a workpiece by using a saw-milling cutter. The saw-milling was also performed for a complete parting-off operation. The cutter and the workpiece are set in a manner so that the cutter is directly placed over one of the T-slots of the table.
11. Milling Key Ways, Grooves and Slots
This operation is used to produce keyways, grooves, and slots on the workpiece.
The operation of producing keyways, grooves, and slots of varying shapes and sizes can be performed in a milling machine. It is done by using a plain milling cutter, a metal slitting saw, an end mill, or a side milling cutter.
The open slots can be cut by a plain milling cutter, a metal slitting saw, or a side milling cutter. The closed slots are produced by using endmills. A dovetail slot or T-slot is manufactured by using special types of cutters designed to give the required shape to the workpiece.
The second slot is cut at right angles to the first slot by feeding the work past the cutter. A woodruff key is designed by using a woodruff key slot cutter. Standard keyways are cut on the shaft by using side milling cutters or end mills. The cutter is set exactly at the centerline of the workpiece and then the cut is taken.
12. Gear Milling
This milling process is used to cut gears on the workpiece. The involute gear cutters are used in this operation.
The gear cutting operation is performed in a milling machine by using a form-relieved cutter. The cutter may be a cylindrical type or end mill type. The cutter profile fits exactly with the tooth space of the gear. Equally spaced gear teeth are cut on a gear blank by holding the work on a universal diving head and then indexing it.
13. Helical Milling
It is used to produce objects having a helical design like helical gears, twisted drills, etc. and it is performed on the periphery of a cylindrical workpiece.
Helical milling is the operation of producing helical flutes or grooves around the periphery of a cylindrical or conical workpiece. The operation is performed by rotating the table to the required helix angle. And then by rotating and feeding the workpiece against rotary cutting edges of a milling cutter.
Production of the helical milling cutter, helical gears, cutting helical grooves or flutes on a drill blank or a reamer.
14. Cam Milling
This milling operation is used to make cams. These cams are used to open and close the valves in the IC engines.
15. Thread Milling
The thread milling machine operations are used to produce threads by using a single or multiple thread milling cutter. Thread milling operation is performed in special thread milling machines to produce accurate threads in small or large quantities.
The operation requires three driving motions in the machine. One for the cutter, one for the work, and the third for the longitudinal movement of the cutter.
Safety Rules for Milling Machines
Milling machines require special safety precautions while being used:
- Do not make contact with the revolving cutter.
- Place a wooden pad or suitable cover over the table surface to protect it from possible damage.
- Use the buddy system when moving heavy attachments.
- Do not attempt to tighten arbor nuts using machine power.
- When installing or removing milling cutters, always hold them with a rag to prevent cutting your hands.
- While setting up work, install the cutter last to avoid being cut.
- Never adjust the workpiece or work mounting devices when the machine is operating.
- Chips should be removed from the workpiece with an appropriate rake and a brush.
- Shut the machine off before making any adjustments or measurements.
- When using cutting oil, prevent splashing by using appropriate splash guards. Cutting oil on the floor can cause a slippery condition that could result in operator injury
Advantages of Milling Machine
Following are the advantages of the Milling machine:
- The size and durable construction of the milling machine give tremendous support to handle large and heavier machines without damaging itself.
- It provides flexible computer control options for cutting purposes.
- It reduces the chances of human errors.
- It assures accurate cuts.
- Availability of customization.
- Use of multiple cutters.
- It can do multiple cuts simultaneously.
- Milling is perfect for producing individual pieces in small or large batches.
- It has the capability of producing complicated shapes, using multi-tooth and single point cutting tools.
- The operation costs can be controlled to a great extent if general-purpose cutters and equipment are used.
- Greater precision in the finishing of the work compared to other machines.
Disadvantages of Milling machine
There are several disadvantages to milling machines:
- The cost of the milling machine is high.
- As milling cutters cost high, the investment for procuring tools is more.
- The production cost will increase if we carry out the operations performed in a shaper or a drilling machine with a milling machine.
- The CNC milling machine and setup are more expensive than manual instruments.
- The workers who operate milling machines need proper training
- It takes a period of time for design and programming, not so cost-effective for small amounts of products.
Application of Milling machine
The applications of Milling Machine are as follows.
- The milling machine is used for making various types of gears.
- It is generally used to produce slots or grooves in workpieces.
- It can able to machine flat surfaces and irregular surfaces too.
- It is used in industries to produce complex shapes.
- It is used in Institutions or colleges to conduct lab tests on a milling machine.