Punch (tool)

For punches used in punch presses, see Punching.

A punch is a hard metal rod with a shaped tip at one end and a blunt butt end at the other, which is usually struck by a hammer. Punches are used to drive objects, such as nails, or to form an impression of the tip on a workpiece. Decorative punches may also be used to create a pattern or even form an image.

Nail or pin

pin punch

A nail punch, also called a nail set, is used to drive the head of a nail flush with or below a surface. A pin punch is a similar tool used to drive pins for affixing a fixture to a rotating shaft. Nail and pin punches have a body by which the punch is held, with a flat ended cylindrical section whose diameter suits the object to be driven.

Center

A center punch

A center punch is used to mark the center of a point. It is usually used to mark the center of a hole when drilling holes. A drill bit has the tendency to "wander" if it does not start in a recess. A center punch forms a large enough dimple to "guide" the tip of the drill bit.^[1] When drilling larger holes, and the web of the drill is wider than the indentation produced by a center punch, the drilling of a pilot hole is usually needed.

An automatic center punch operates without the need for a hammer.

Prick

A prick punch

A prick punch is similar to a center punch but used for marking out. It has a sharper angled tip to produce a narrower and deeper point. The mark can then be enlarged with a center punch for drilling.^[1]

Transfer

transfer punch

A transfer punch is a punch (usually in an index set) of a specific outer diameter that is non-tapered and extends the entire length of the punch (except for the tip). It is used to tightly fit the tolerances of an existing hole and, when struck, precisely transfer the center of that hole to another surface. It can be used, for example, to duplicate the hole patterns in a part, or precisely set locations for threaded holes (created by drilling and tapping) to bolt an object to a surface.

Doming

Doming punches

A doming punch is used in conjunction with a doming block to make spheres or hemispheres out of sheets of metal. The punch is generally made of tool steel, but can be made of wood. They come in a number of different sizes, the punch size determining what size the finished product will be.

Drift

drift punch

Main article: Drift pin

A drift "punch" is misleadingly named; it is not used as a punch in the traditional sense of the term. A drift punch, or drift pin, is used as an aid in aligning bolt or rivet holes prior to inserting a fastener. A drift punch is constructed as a tapered rod, with the hammer acting on the large end of the taper. The tapered end of a drift punch is placed into the semi-aligned bolt holes of two separate components, and then driven into the hole. As it is driven in, the taper forces the two components into alignment, allowing for easy insertion of the fastener. Unlike most punches, force is never (and should never be) applied to the tip, or end of a drift pin.

Decorative

Punches with a decorative motif have been used to create patterns or images on metals and various other materials, notably leather. In goldsmithing, bookbinding and armour-making the technique is called pointillé. In printmaking punches were used to create most of the image in the plates for printing metalcuts.

Letter

Letter stamps

Also known as letter stamps or number stamps. These are used to emboss the impression of a letter or number into a workpiece. They are most common in the reverse image, this allows the end result to be immediately readable, however they may be made as a positive image. This is essential in the case of die or mold making and ensures that the finished product will be readable, as a die is a negative image.

Tablet press

These punches are a part of tablet press. Unlike most punches, tablet press punches have a concave ending in the shape of the desired tablet. There are the lower and the upper punches to compress the powder in between.

See also

• Punchcutting

References

1. ^ ^{a b} Fournier, Ron; Fournier, Sue (1989), Sheet metal handbook, HPBooks, pp. 21–22, ISBN 9780895867575, http://books.google.com/books?id=ViUmhImu630C&pg=PA21