Surface feet per minute (SFPM or SFM) is the combination of a

physical quantity A physical quantity is a physical property of a material or system that can be quantified by measurement. A physical quantity can be expressed as a ''value'', which is the algebraic multiplication of a ' Numerical value ' and a ' Unit '. For examp ...

(''surface speed'') and an

imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texa ...

and American customary unit (''feet per minute'' or ''FPM''). It is defined as the number of linear feet that a location on a rotating component travels in one minute. Its most common use is in the measurement of cutting speed (surface speed) in

machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

. It is a

unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (alb ...

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...

that describes how fast the cutting edge of the

cutting tool In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...

travels. It correlates directly to the

machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...

of the workpiece material and the

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

of the cutting tool material. It relates to

spindle Spindle may refer to: Textiles and manufacturing * Spindle (textiles), a straight spike to spin fibers into yarn * Spindle (tool), a rotating axis of a machine tool Biology * Common spindle and other species of shrubs and trees in genus ''Euony ...

speed via variables such as cutter diameter (for rotating cutters) or workpiece diameter (for

lathe A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to c ...

work). SFM is a combination of ''diameter'' and the ''velocity'' (

RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

) of the material measured in feet-per-minute as the

of a

milling machine Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying direction on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of d ...

. 1 SFM equals 0.00508 m/s (meter per second, the SI unit of speed). The faster the spindle turns, and/or the larger the diameter, the higher the SFM. The goal is to tool a job to run the SFM as high as possible to increase hourly part production. However some materials will run better at specific SFMs. When the SFM is known for a specific material (''ex 303 annealed stainless steel = 120 SFM for high speed steel tooling''), a formula can be used to determine spindle speed for live tools or spindle speeds for turning materials. In a milling machine, the ''tool'' diameter is used instead of the ''stock'' diameter in the following formulas when the tool is revolving and the stock is stationary. Spindle speed can be calculated using the following equation: :

\text = \frac \approx \frac

Brown & Sharpe; ''Brown & Sharpe Automatic Screw Machine Handbook'', Publisher B&S SFM can be calculated using the following equation: :

SFM = \text \times \pi \times \frac \times \text \approx \text \times 0.2618 \operatorname

References

{{Reflist

External links

Surface Feet per Minute
Machining Units of velocity Metalworking terminology Velocity

See also

References

External links