Why are CNC lathes more expensive than a CNC Mill

I have a Sieg KX1 milling machine and have been considering a new little CNC lathe to compliment the Sieg. But what I can't understand is why the CNC lathes are more expensive than the CNC milling machines!

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After all, the lathe has one less axis to equip with a motor and ball screw and controllers etc. And a lathe is relatively simple to make with a bed and head stock, it may not even need a tail stock, and a manual tool change would be okay with me.

In the UK I have a limited choice of new machines, Wabeco CNC are over priced, so Axminster Tools and machinery are probably the place to go to, but their small machines start at £9,799 rising to £16,659 also a bit too much for what they are! Their Mills start at £6,675 (KX1 in a metal box) to £14,998.

I've been following Roger Webb on Youtube with his excellent Mini Lathe CNC conversion so maybe this is the way to go.

So as the thread title asks &#; does any one know? why do CNC lathes cost more than CNC milling machines? Can we compare like for like?

Ian

If you&#;re looking for a lathe, then you&#;re probably already acquainted with the basics of what a lathe is, what it does, and the various uses it has for professionals and hobbyists alike. But if you don&#;t know much about lathes, rest easy! We&#;ll start with a basic history of the lathe, give some general information on what a lathe does, then move on to provide more guidelines on how to pick a lathe for a given project. 

Lathes, in their earliest form, were a two-man, manually operated machine. Of course, that early form was over three millennia ago in ancient Egypt, so things were understandably a bit more old-school.

Even the early lathes possessed the key feature of all lathes, from then till now; unlike other machine tools, in a lathe, the item being cut or shaped (the &#;workpiece&#;) is the thing that turns, not the cutting instrument. A lathe is the reverse of a drill; rather than a spinning cutting bit biting into a surrounding piece of wood or metal, a spinning piece of metal is shaped by a stationary cutting head.

Thanks to a lathe&#;s design, shaping a workpiece on a lathe is known as &#;turning&#; a piece. Nearly any kind of material can be worked on a lathe, though metal and wood are the most common ones. 

The development of the lathe

Lathes started as fairly primitive tools, but took a giant leap forward during the Industrial Revolution. Steam engines provided more powerful lathes; electricity would develop lathes even further. In the s, servomotors added elements of control to the turning process, and today&#;s lathes are fully integrated with Computer Numerical Control (CNC), allowing them to be fully automated.

Along the way, craftsmen explored what could be done with a lathe. Lathes allow material to be removed to create rounded shapes; everything from metal shafts to wooden chair legs can be shaped out of irregular pieces using a lathe. Today, you&#;ll find lathes everywhere from fine woodworking shops to cutting-edge factory floors, serving different purposes but using the same principle; a spinning workpiece with a stationary cutting head.

Purpose of your new lathe

If you&#;re considering buying a lathe, you first need to picture the primary project or projects you&#;ll be using the lathe for. With the project in mind, here are some questions to ask which will guide your choice of a lathe.

• Are you cutting primarily wood pieces, or is this a metal-cutting lathe? 
• WIll it be in a personal workshop, or a modern tool-and-die shop?
• Do you need full automation, or is a simple machine better?

These factors influence the complexity of the lathe you&#;ll need. A fully CNC-equipped lathe able to handle industrial-sized pieces along four axis, with multiple heads for turning, drilling and cutting, is vastly different from a simple, two-axis lathe for turning furniture.

Components

When it comes to the parts you&#;ll be putting into the lathe, there are more factors. Basic components of a lathe consist, generally, of the following:

• Headstock with spindle
• Chuck (to hold the workpiece)
• Lathe bed
• Carriage and cross-slide
• Tool turret
• Tailstock

The specifications you&#;ll need for those components is determined by the general intended purpose for your lathe, and the dimensions of the pieces you&#;ll be working on. 

Headstock with spindle &#; Found on the left-hand side of the lathe, the headstock holds the spindle in place, usually with bearings. Usually with a motor and pulley, the headstock also provides the power to rotate the spindle and part, The size of the spindle varies, typically from ½ inch to 1 ½ inches in diameter.

The size of the spindle determines how big of a workpiece you can turn on your lathe. A one-inch spindle may be enough for smaller work, but for a spindle that&#;s sturdy enough to accommodate larger pieces without flexing, you&#;ll often need at least an inch-and-a-quarter spindle.

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Other headstock and spindle considerations to be aware of: does the headstock allow outboarding? While pieces are intended to be mounted between the headstock and tailstock, over the bed of the lathe, outboarding allows the workpiece to be mounted away from the body of the piece.

This greatly increases the diameter of the pieces that can be turned. It&#;s not an ideal fix; there are good reasons why pieces are typically mounted over the bed of the lathe, where the tool turret is located and the tailstock helps to support the workpiece. Regardless, when you purchase a lathe, consider the size of the headstock and spindle, and the different positions the headstock allows. Some headstocks can actually be rotated, allowing outboarding more easily.

Chuck &#; The chuck is the specialized clamp to hold a cylinder. The chuck holds the workpiece, and most lathes can secure workpieces between 5 and 66 inches. Many chucks also have a through-hole, allowing long pieces to extend through the chuck and out behind the lathe. Use the same decision-making process with a chuck as with the headstock; what size do you need based on the pieces you&#;re likely to be working?

Note that there are extra options with chucks also; most chucks are jawed, which are the movable parts tightened or loosened to fit the workpiece. Typical jaw arrangement is three or four jaws on each chuck, but some chucks have many more. The jaws may be tightened together, or moved independently to help hold odd-shaped pieces.

Lathe bed &#; The bed of the lathe is a simpler decision. There are two basic options; the British flat bed, or the American-preferred v-bed. The two kinds are self-explanatory, and each of the designs have their proponents. For smaller lathes (and correspondingly smaller workpieces), it rarely makes much difference to the performance of the lathe.

On larger, more industrial-oriented lathes, beds can also be rounded, and slant-bed lathes are increasingly common on fully-automated CNC lathes in industrial applications.

Tailstock &#; On many new lathes, the tailstock is an optional feature. Its purpose is a simple one &#; it holds the far end of the workpiece. While a tailstock may not be necessary for smaller pieces, for larger parts a tailstock is crucial. Using a tailstock reduces flex in the workpiece; too much flex can give a finished piece an undesirable warp or curve. If you&#;re going to be handling larger pieces, purchasing a tailstock from the beginning is a smart choice.

Carriage, cross-slide, and turret &#; These are the &#;business parts&#; of the lathe. The carriage is a set of bars, often two or three, running the length of the lathe. The cross-slide rests on the carriage, and holds the turret. The turret, in turn, houses the different cutting and boring tools to be used on the part.

While this sounds complicated, just now that it is the carriage and cross-slide which determine the number of axis on which your lathe can move, whether that be two, three, or four. The size of the turret, and the number of heads which it can hold, is determined by the size of the piece you want to turn. Larger workpieces require larger cutting heads, which in turn require larger turrets.

Further considerations

Size &#; In the US, you&#;ll find lathes described as &#;8 in. by 24 in.&#; lathes. The latter number refers to the distance between centers (i.e., the headstock and tailstock), or the longest piece of material that lathe can handle. The first number, in the US, pertains to the maximum diameter a workpiece can have and still be above the lathe bed. This is also known as the &#;swing&#; of the lathe.

In the UK, the first number is expressed differently; as the measure between the center of the chuck, so in theory the center of any workpiece, and the closest point of the bed of the lathe. An 8 by 24 lathe in the US would therefore be a 4 by 24 lathe in the UK.

Most hobbyists and craftsmen working on smaller pieces will find that a 3&#; x 15&#; lathe is typically as small as one should go, while about double that size, 6&#; x 30&#;, forms the upper end of what a home lathe can be.

Weight &#; Be aware that like many pieces of machinery, lathes can be quite heavy. The sizing as given is not the dimension of the lathe itself, but rather of the workpiece which can be accommodated; the lathe will be significantly larger. A 3&#; x 15&#; lathe can easily weigh more than 30 kg; a lathe double that size would weigh far more, and require an engine lift or small crane to move into place.

Power &#; One of the last things you&#;ll need to consider when buying a new lathe is the motor. While some lathes operate at a single speed, many will have multiple speed settings. There is also the matter of torque to consider.

For cutting larger pieces, your lathe will need more than just high RPMs; it will need the power to keep a heavy workpiece turning and cutting smoothly. Advertisers may proudly proclaim maximum RPMs for their lathes; but minimum RPMs can be even more important for operations such as screwcutting. 

Axis &#; Lathes have at least two axis of movement: an X axis (forward/backward along the cross-slide), and Y (perpendicular to the X axis). However, a high-end CNC lathe may have as many as 7 axis, from X, Y, and Z (three-dimensional movement) to rotating axis. So, axis X may have additional axis of movement A, which is a rotational along the X axis.

This may sound confusing; suffice it to say, that the more axis of movement a lathe has, the more complicated, expensive, and industrial it is likely to be.

Buying a lathe is a bit of a complicated process, but you&#;ll be helped immensely if you keep the project in mind as you shop. What are you intending to use the lathe for? With that project as the determining factor, the necessary complexity of the lathe and any size or weight restrictions will become apparent. You&#;ll be able to make a much more informed decision if you keep the needs of your project foremost.

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