Planer (metalworking)
A planer is a type of metalworking machine tool
Machine tool
A machine tool is a machine, typically powered other than by human muscle , used to make manufactured parts in various ways that include cutting or certain other kinds of deformation...

 that uses linear relative motion between the workpiece and a single-point cutting tool
Tool bit
The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or...

 to machine a linear toolpath. Its cut is analogous to that of a lathe
A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...

, except that it is (archetypally) linear instead of helical
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

. (Adding axes of motion can yield helical toolpaths; see "Helical planing" below.) A planer is analogous to a shaper
A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is linear instead of helical...

, but larger, and with the entire workpiece moving on a table beneath the cutter, instead of the cutter riding a ram that moves above a stationary workpiece. The table is moved back and forth on the bed beneath the cutting head either by mechanical means, such as a rack and pinion
Rack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...

 drive or a leadscrew
A leadscrew , also known as a power screw or translation screw, is a screw designed to translate turning motion into linear motion...

, or by a hydraulic cylinder
Hydraulic cylinder
A Hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in engineering vehicles.- Operation :...


Linear planing

The most common applications of planers and shapers are linear-toolpath ones, such as:
  • Generating accurate flat surfaces. (While not as precise as grinding, a planer can remove a tremendous amount of material in one pass with high accuracy.)
  • Cutting slots (such as keyways).
  • It is even possible to obviate wire EDM
    Electrical discharge machining
    Electric discharge machining , sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion, is a manufacturing process whereby a desired shape is obtained using electrical discharges...

     work in some cases. Starting from a drilled or cored hole, a planer with a boring-bar type tool can cut internal features that don't lend themselves to milling or boring (such as irregularly shaped holes with tight corners).

Helical planing

Although the archetypal toolpath of a planer is linear, helical toolpaths can be accomplished via features that correlate the tool's linear advancement to simultaneous workpiece rotation (for example, an indexing head
Indexing head
An indexing head, also known as a dividing head or spiral head, is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions...

 with linkage to the main motion of the planer). To use today's terminology, one can give the machine other axes in addition to the main axis. The helical planing idea shares close analogy with both helical milling
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

 and single-point screw cutting. Although this capability existed from almost the very beginning of planers (circa 1820), the machining of helical features (other than screw threads themselves) remained a hand-filing
File (tool)
A file is a metalworking and woodworking tool used to cut fine amounts of material from a workpiece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one...

 affair in most machine shops until the 1860s, and such hand-filing did not become rare until another several decades had passed.

Prevalence of current use

Planers and shapers are now obsolescent, because other machine tools (such as milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

s, broaching machines, and grinding machine
Grinding machine
A grinding machine, often shortened to grinder, is a machine tool used for grinding, which is a type of machining using an abrasive wheel as the cutting tool...

s) have eclipsed them as the tools of choice for doing such work. However, they have not yet disappeared from the metalworking world. Planers are used by smaller tool and die shops within larger production facilities to maintain and repair large stamping dies and plastic injection molds. Additional uses include any other task where an abnormally large (usually in the range of 4'×8' or more) block of metal must be squared when a (quite massive) horizontal grinder or floor mill is unavailable, too expensive, or otherwise impractical in a given situation. As usual in the selection of machine tools, an old machine that is in hand, still works, and is long since paid-for has substantial cost advantage over a newer machine that would need to be purchased. This principle easily explains why "old-fashioned" techniques often have a long period of gradual obsolescence in industrial contexts, rather than a sharp drop-off of prevalence such as is seen in mass-consumer technology fashions.

Configurations and sizes

There are two types of planers for metal: double-housing and open-side. The double-housing variety has vertical supports on both sides of its long bed; the open-side variety has a vertical support on only one side, allowing the workpiece to extend beyond the bed. Metal planers can vary in size from a table size of 30"×72" to 20'×62', and in weight from around 20,000 lbs to over 1,000,000 lbs.


Early planing ideas are known to have been underway in France in the 1750s. In the late 1810s, a variety of pioneers in various British shops (including James Fox
James Fox (engineer)
James Fox,fl 1780-1830, machine tool maker, was originally a butler in the service of the Rev. Thomas Gisborne, of Foxhall Lodge, Staffordshire. He had a strong interest in handicraft and his employer not only encouraged him, but enabled him to set up in business on his own account.The growth and...

, George Rennie
George Rennie (engineer)
George Rennie was an engineer born in London, England. He was the son of the Scottish engineer John Rennie and the brother of Sir John Rennie.-Early life:...

, Matthew Murray
Matthew Murray
Matthew Murray was an English steam engine and machine tool manufacturer, who designed and built the first commercially viable steam locomotive, the twin cylinder Salamanca in 1812...

, Joseph Clement
Joseph Clement
Joseph Clement was a British engineer and industrialist, chiefly remembered as the maker of Charles Babbage's first Difference engine, between 1824 and 1833.-Early life:...

, and Richard Roberts
Richard Roberts (engineer)
Richard Roberts was a British engineer whose development of high-precision machine tools contributed to the birth of production engineering and mass production.-Early life:...

) developed the planer into what we today would call a machine tool. The exact details have been contentious and will probably never be known, because the development work being done in various shops was undocumented for various reasons (partially because of proprietary secrecy, and also simply because no one was taking down records for posterity). Roe (1916) provides a short chapter that tells the story as thoroughly as he was able to discover it.

External links

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