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 the purpose of a milling machine?
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.
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.
The exact operations a milling machine can perform depend both on the structure of the mill (horizontal or vertical) and the tooling equipped to it. End milling requires a tool that closely resembles a drill bit; face milling uses one with a wider cutting end, more suitable for finishing surfaces. End mills and face mills aren’t entirely separate kinds of milling machines, but rather machines that have been equipped to perform certain operations.
Milling machines differ from metal lathes by the rotation of the tool rather than the part. And unlike lathes, where a workpiece is mounted between the headstock and tailstock but above the bed, most mills fasten the workpiece directly to the bed.
Rather than lathes, vertical mills in particular closely resemble wood routers in their function, but heavy-duty milling machines are more likely to be found in a metal machinist’s shop rather than a woodworker’s workshop.
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.
What to consider when purchasing a milling machine
So when it comes time to purchase a milling machine, what do you need to consider? There’s no one universal milling machine; every machine will likely be better at some operations than others. But before you make your choice, consider these three primary considerations:
Size matters. If you need a machine that can handle industrial-sized workpieces, you need an industrial-sized mill. You might want a reinforced milling head on a vertical mill, or you might decide to jump straight to a horizontal mill.
Mini milling machines are smaller than their full-size counterparts, but just how small do you need? Some mini mills are your typical benchtop mills; still capable of handling sizeable parts, but small enough to fit on top of a worktable in your shop.
On the other hand, some mills fall into the “micro milling machine” category; truly small mills for intricate or detailed work, for example on jewelry.
Remember also that there’s a stability trade-off with smaller mills. In general, the larger the mill, the more stable it is. Mills can be clamped to the top of a workbench or bolted directly to the floor; the latter is preferable if you need precise and heavy-duty cutting. Metal fabrication shops handling larger pieces of metal will want either full-size mills or larger benchtop models. While clamping your mini mill on top of a bench offers substantially more accessibility and ease of use, it comes at the expense of some stability.
It’s no surprise that most ads for milling machines start with a list of features. Milling machines need to be useable, and the more features your mill has, the more useable it will be.
What features should you look for? A shortlist should include:
- Digital readouts – while not entirely necessary, digital readouts make a mill much more user-friendly. They’ll also help the operator keep cuts accurate and precise.
- 3- or 4-axis movement – the more axes of movement, the greater the range of operations possible on that mill. X-axis, Y-axis, and Z-axis movement is the standard. Tools with more axes will likely be able to swivel the cutting tool around the part, engaging it from different angles. Or, in the case of mills with a rotary table, the workpiece itself can swivel, providing access without re-mounting the part.
- Cast-iron construction – cast iron isn’t just sturdy, it’s heavy. Weight, on a mini mill, is a good thing. It adds stability and improves precision.
- Spindle speed and horsepower specs – high-speed spindles and heavy-duty horsepower engines increase drilling capacity.
- Head tilt – many mills have geared heads capable of cutting at an angle, adding flexibility.
For the ultimate in precision cutting, you’ll want a CNC mill. Computer numerical programming allows an operator to program the exact series of operations for the mill to make, allowing extremely precise and accurate cuts.
However, adding CNC capabilities will make your new mill considerably more expensive. It will also add to the learning curve for your new mill. On the other hand, you’ll be able to create more precise cuts and smooth finishes with the aid of CNC programming, and the actual operation of the mill is simplified.
CNC mills can also be more easily integrated with design workflows. A hobbyist might design a custom part on a CAD program, export the vector file to his CNC mini mill, and create a custom program to fabricate his part.
However, in many applications, the task at hand does not require CNC capabilities. For these tasks, a manual mini mill will suffice and may be cheaper to purchase than a CNC machine. Manual mills are designed for use by only one person and have no computer-controlled movement of any kind. This makes them more affordable than their CNC counterparts, though they are also correspondingly less precise.
While it’s true many milling machines are costly >$10,000+, there are many affordable options to fit every budget.
So, how much does a good milling machine cost?
- For a hobbyist router, the price is roughly $2,500-$3,500 for a solid machine.
- CNC Routers start as low as $5,000 and rise to >$75,000.
- 3-Axis Mills are generally $45,000 and goes as high as $100,000
- Professional product mills and lathes are $250,000+ depending on size and features. These machines are found in enterprise shops and for machining complex, large parts.
Mini milling machines: versatile versions of industrial counterparts
Milling machines traditionally are found as part of heavy industry. Mini milling machines are simply smaller versions of their larger counterparts, suitable for use in small machine shops or home workshops. These are also known as benchtop milling machines, at home in a variety of situations.
Most mini milling machines are vertical mills, making them highly versatile. The addition of CNC – Computer Numerical Control – technology to mini milling machines means that modern mini mills can be used for a wide variety of applications. Variable speed control allows operators to adjust for cutting different materials, adding more versatility.
The world of mini milling machines is the same as larger versions, just smaller. The most common types of work done by these devices are sand casting patterns for metal foundries and selective machining such as drilling holes or making slots in a material. These models often feature an indexable table that moves up and down to allow access to the workpiece.
Tips when buying a milling machine
Now that you know what you need from the milling machine itself, what should you look for in a good milling machine manufacturer?
- Wide product range
- Look for companies catering to the machinist industry, selling high-quality lathes and mills of all shapes and sizes.
- Excellent customer support
- Customer support doesn’t just come after a sale; reach out to companies for advice, and look for the companies who are willing to guide you through the purchasing process, not just sell you a more expensive machine. Also, check the warranty policy for each machine and manufacturer.
- Detailed specialist knowledge
- The world of machine tools includes some specialist and hobbyist fields, such as micro mills, jewelry machine tools, or DIY. If applicable, look for a company that serves your niche.
- Quality construction
- From collet to shank, the best machine tool manufacturers use only the best parts. Look for a company that doesn’t skimp on quality components, and you’ll find one that produces high-end milling machines.
Our Choice: The Jr. Table Top Mill
A great example of a classic tabletop milling machine is the CNC Masters Jr. A quick look at the specifications for this tabletop mill shows everything you would expect to find – 3-axis movement, 2 HP motor, and a 28-3/4 x 8-1/4″ table area. The whole package weighs 700 lbs – light enough for a heavy-duty workbench, heavy enough to provide valuable stability.
While the CNC Masters Jr. won’t ever be mistaken for a micro mill, it’s a good example of a classic tabletop model, with a full range of features in a smaller package. It’s aimed squarely at small machine shops or home-based workshops for DIY-ers and hobbyists.
What do you need to know before you purchase a mini milling machine? Remember the following:
- What you will use the milling machine for
- Exact specifications/capabilities required
- Qualifications of the manufacturer
Follow those guidelines, do your research, and you’ll be well on your way to getting the most out of your new mini milling machine.