What is a Milling Machine?
A mill is an advanced machining tool that helps you with even the most rigorous of applications.
The scope of work you can carry out with a milling machine is vast. At one end of the spectrum, you can rip grooves through steel while at the other extreme, you can create or modify tiny components in a fashion no other tool permits. While the heavier mills capable of real grunt work can weigh several tons, you can also get much smaller milling machines fit for the home hobbyist without a wealth of machining experience to fall back on.
In a nut, milling is a cutting process. It harnesses a milling cutter in order to remove material. This is a rotary cutting tool that commonly has multiple cutting points. The cutter moves perpendicular to the axis unlike drilling where the tool moves along the rotation axis. When the cutter hits the workpiece, its edges – called teeth or flutes – rapidly cut then exit the material. This shaves off chips with each pass. These chips are called swarf. The number of teeth and the speed of the cuts are tweaked according to the material and application.
The original milling machines evolved into CNC (computer numerical control mills) but these highly advanced machines are not generally used in the home and fall outside the remit of today’s article.
Setting aside the CNC mills, we’ll look now at the main types of mill used in the home workshop before we move on to our milling machine reviews…
We will look at the broad categories of horizontal milling machines and vertical milling machines. This distinction is based on whether the spindle axis runs side to side or up and down. Although tilting and swiveling can permit some degree of cross-functionality, there are some tasks that are much easier on one style of machine.
We’ll give you a little more detail now on the strengths and weaknesses of each type of milling machine…
HORIZONTAL MILLING MACHINE
A horizontal mill has the spindle mounted so it’s parallel to the plane of your table.
Some horizontal milling machines have an integrated rotary table so you can mill at different angles for greater flexibility.
The over arm on these machines braces the arbor on both sides. The outstanding rigidity this provides means you can make much heavier cuts than a vertical milling machine allows and you’ll enjoy a super-swift removal rate. The strength is so great you can stack a number of cutters in the arbor. This means you can tackle much more ambitious projects in an extremely efficient, time-saving fashion.
Horizontal milling machines comes into their own for cutting slots and grooves. You use side mills and face mills for these cutting tasks. For surfacing, get yourself a plain mill. You can also get specialty cutters although these are pretty expensive. You’ll be able to cut gears on one of these hard-hitting mills.
When it comes to the spindles, a simplex mill has just one while a duplex mill has a pair of spindles.
The significant flipside of horizontal mills is the difficulty you’ll encounter if you need to make parts with cuts in all axes.
VERTICAL MILLING MACHINE
A much more adaptable approach to milling is a vertical milling machine. Although they demand a little more time invested, there’s very little a vertical mill can’t do
The spindle axis on these machines runs vertically. The spindle holds the cutters in place and they rotate along the spindle’s axis. You can perform plunge cuts and perform drilling work by extending the spindle or manipulating the table.
Now we’ve wrapped up our milling machine reviews, we’ll give you some guidance on getting the right mill for your needs after an exploration of who needs this kind of machine in the first place…
Who Needs Milling Machines?
If you want to make or modify small parts using a range of materials, the best milling machine is indispensable.
Unlike many power tools and machinery, it’s certainly not something to buy just in case. It’s a specialist machine capable of performing extremely exacting work to a very high standard. For this reason, milling machines are not cheap so it pays to think long and hard before stumbling in.
3D printers are becoming less expensive and more able but, when it comes to creating small components, there’s still nothing to touch a milling machine.
Here are just a few of the jobs you can carry out with the best milling machine:
- Machine flat surfaces
- Make irregular surfaces
- Cut gears
- Create slots
- Cut grooves
Whether it’s a manually controlled machine for a home hobbyist or a CNC machine for heavy industrial work, milling machines stand in a class of their own so we’ll move on now to some basics you should take into account if you’re on the lookout for one of these wonderful versatile machines.
The most important thing straight off the bat is to think very carefully about what you intend to do with your milling machine. This will determine the category of mill you should choose.
Price always plays a part in any buying decision. With milling machines, the discrepancy is vast. You can pay a few hundred dollars or tens of thousands of dollars depending on what kind of functionality you’re looking out for. Clearly, the average home user is not looking for a CNC beast weighing several tons so we’ve limited our reviews to machines more likely to find a home in a small workshop.
Unfortunately, with milling machines there are not a large number of accurate and meaningful reviews. Nevertheless, try to do as much research as you can including a look at the manufacturer’s own website so you can gather as much information as possible.
Visit forums and check out user reviews so you can get some frank feedback from people who have purchased the mill you have in mind. Pay close attention to the disadvantages rather than focusing only on what they do well.
Beyond that, take the time to look through our concise buying guide so you know exactly what to look out for when you’re buying a mill…
What To Consider When Buying a Milling Machine
It’s always a toss-up when you buy any product at all whether to spend heavily on a reputable brand or try to shave off a few dollars and place your trust in a lesser-known manufacturer.
In principle, any manufacturer could make a perfectly sound milling machine. These machines have been around for a long time and there’s nothing to stop any brand from turning out a great example.
In practice, though, most cheap mills will make use of cheaper materials. The motors are likely to be insufficiently powerful. Machining might not be up to scratch leaving you with a mill incapable of delivering the precise tolerances you need.
Overall, we would strongly recommend rolling with a brand you can trust, one that has some heritage when it comes to making milling machines. If you are going with an unknown quantity, make sure you do your due diligence to avoid ending up with a lemon.
While it might seem like a wise idea to get a tiny desktop mill, if you plan to work with metal this is unlikely to yield the results you are looking for. Working with metal, in particular, demands plenty of force and can be hard going. It’s senseless to make things more difficult by buying a milling machine that’s simply too small for the jobs you have in mind.
That said, if you plan to work primarily with wood on a smaller scale, it’s equally senseless to lash out on a colossal mill providing needless power and performance.
Although size matters, with milling machines it’s very much a case of getting equipment aligned with the projects you’ll most frequently undertake.
A good rule of thumb is to opt for a mill that’s as heavy, large and rigid as you can comfortably accommodate in your workshop that falls within your budget. Flexing of any sort is the enemy of precision when you’re milling so choose something that’s rigid enough for the materials you’ll be using and powerful enough not to become overworked.
Here, the size of the components you’ll be machining should inform your buying decision.
There are 4 main areas to consider related to capacity:
Table Size: You won’t be strictly limited to working with material the same size as the table. You can always support pieces that overhang in any direction. The problem, though, is accessing the controls comfortably if you are compromised in this way by material too bulky for the size of the table. Stability can also be adversely affected. Also, since you generally want to affix a vise to the table and clamp your material down, size of the table is a mitigating factor and one you should give due weight when you’re buying a milling machine
Maximum Distance from Table to Spindle: This is a factor on all milling machines where the table is fixed and the spindle moves up and down. The dimension here concerns the spindle when it’s at its highest point. This measurement corresponds to the highest workpiece you can safely place on your mill. Don’t forget the height of the collet and any tools you’ll be using when you’re mulling over this maximum distance
Table Travel (Cross and Longitudinal): The table of a milling machine can move backwards and forward (cross) and from side to side (longitudinal). The distances of travel relate to the maximum safe working area you can use without being forced to reposition your work
Quill Travel: This measurement is for the maximum depth of the holes and slots you’ll be able to cut
- Materials You Will Work With
Think about what materials you plan to machine as this will play an important role in the type of milling machine that makes the best fit.
Aluminum, Plastic, Brass and Composites: Vertical mills make a great fit for these materials. If you have no intention of machining steel, you could also opt for a mini mill-drill
Steel: Floor-standing vertical mills are essential if you plan to work with steel. A mill-drill will not be man enough for the job. As well as rigidity and a solid base, you’ll also need a milling machine with enough poke to power the cutters so they’ll cut through steel
- Speed and Power
Since milling can call for extreme forces, a powerful motor is a prerequisite.
Most mini-mills have motors of at least 1HP which is the minimum size you should shoot for. Double this if you are looking at floor-standing mills.
Micro-mills are a little different. You can drop down to a 1/8HP, 100-watt motor. This will generate more than enough power for a miniaturist tool.
Since you’ll machine different material at different rates, it’s crucial to choose a mill with variable speed. Most serviceable mills have 8-12 speeds while a few allow you to choose any speed within the minimum and maximum parameters.
The feed rate is the speed at which the cutter passes through the workpiece. This will influence the finish quality.
Smaller micro-mills and mill-drills usually have handles so you can manually feed the material.
Industrial milling machines often feature powered feed systems. While this is something also available in a few mills suitable for smaller shops, it’s a costly extra so think twice about whether you really need this functionality.
As well as a mill that’s solid and very rigid, the precision of the controls themselves play a part in overall accuracy.
Look for hand controls that permit coarse or fine movement. Depth stops and gauges are also important. An accurate scale with small increments also helps to achieve a superior finish. The saying that a bad workman always blames his tools is particularly apt with milling machines…
While these factors are integral to a decent finish, overall results are influenced heavily by your prowess as an operator. Take your time, learn your craft and you’ll be able to significantly affect accuracy through sheer milling skill.
- Construction of the Mill
Cast iron mills offer superb rigidity which is central to effective milling. Cast iron also goes some way toward dampening the vibration caused by cutting.
The best tables are generally made from precision-ground steel. Aluminum is sometimes used instead but it’s not as strong an option if money is no object.
Above most other power tools, scrutinize the build quality of the mill you have in mind if you want first-class machining and a mill that will last the distance.
Usage and Maintenance Tips
Using a milling machine is a subject so vast it merits a book of its own never mind a small section of an article. Because of the complexity of using these exceptional machines, a short summary will not do it justice.
We’ll focus instead here on safety and maintenance…
Using Your Milling Machine Safely
- Never make contact with the cutter
- Don’t tighten the arbor nuts using machine power
- Install the cutter last when you are setting up your work
- Move heavy attachments with the buddy system
- Always turn the mill off to make any adjustments
- Use splash guards if you’re using cutting oil
- Install and remove cutters using a cloth or rag to avoid cutting yourself
- Get rid of chips using a rake and brush
Maintaining Your Milling Machine
- Never remove the protective paper from cutters until you plan to use them
- Use the right cutting oil to safeguard against overheating
- Keep the cutter away from your vise, chuck and nuts
- Use the correct speed at all times to minimize the likelihood of overheating
- Clean and oil your cutters before storing them
- Make sure the cutters remain sharp at all times
If you give due consideration to these simple pointers, your milling machine will perform at its best and last for years without letting you down.
Neglect this advice and you could end up injured or experience an unexpected breakdown.