In manufacturing

Manufacturing

Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

, an undercut is a special type of recessed surface. In turning

Turning

Turning is the process whereby a single point cutting tool is parallel to the surface. It can be done manually, in a traditional form of lathe, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of...

 it refers to a recess in a diameter. In machining

Machining

Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...

 it refers to a recess in a corner. In molding

Molding (process)

Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 it refers to a feature that cannot be molded using only a single pull mold. In printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

 construction it refers to the portion of the wafer that is etched

Etching (microfabrication)

Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete....

 away under the photoresist

Photoresist

A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....

.

Turning

On turned parts an undercut is also known as a neck. They are often used at the end of the threaded portion of a shaft or screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

 to provide clearance for the cutting tool. For proper usage the undercut should be at least 1.5 threads long and the diameter should be at least 0.015 in (0.381 mm) smaller than the minor diameter of the thread. They are also often used on shafts that have diameter changes so that a mating part can seat against the shoulder. If an undercut is not provided there is always a small radius left behind even if a sharp corner is intended. These types of undercuts are called out on technical drawing

Technical drawing

Technical drawing, also known as drafting or draughting, is the act and discipline of composing plans that visually communicate how something functions or has to be constructed.Drafting is the language of industry....

s by stating the width and either the depth or the diameter of the bottom of the neck.

Molding

Undercuts on molded parts are features that prevent the part from being directly ejected from the injection molding machine

Injection molding machine

An Injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit....

. They are categorized into internal and external undercuts, where external undercuts are on the exterior of the part and interior undercuts are on the inside of the part. Undercuts can still be molded, but require a side action or side pull. This is an extra part of the mold that moves separately from the two halves. These can add 15 to 30% to the cost of the mold and also increase the cost of the molded part.

If the size of the undercut is small enough and the material is flexible enough a side action is not always required. In these cases the undercut is stripped or snapped out of the mold. When this is done usually a stripping plate or ring is used instead of stripper pins so that the part is not damaged. This technique can be used on internal and external undercuts.

Machining

In machining the corners may be undercut to remove the radius that is usually left by the milling cutter

Milling cutter

Milling cutters are cutting tools typically used in milling machines or machining centres . They remove material by their movement within the machine or directly from the cutter's shape .-Features of a milling cutter:Milling cutters come in several shapes and many sizes...

. Examples of this use are linear bearings for square shafts (i.e. racks

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...

) and machined hexalobular sockets.

Etching

Undercuts from etching are somewhat different than the undercuts explained above, because it is a side effect, not an intentional feature. Undercuts from etching can occur from two common causes. The first is over etching, which means the etchant was applied too long. The second is due to an isotropic etchant, which means the etchant etches in all directions equally. To overcome this problem an anisotropic etchant is used.