Punches

A punch is a tool for forcing a pin, bolt, or rivet in or out of a hole. Punches are used with ball-peen hammers to remove pins, align holes and mark locations of holes to be drilled. They are available in a wide range of sizes in both high-carbon and alloy steels. They are similar to nail sets in appearance, but do not have a cupped or hollowed end. It is one of the most popular types of hand tools used for variety of purposes. It is usually in the shape of a hard metal rod having a shaped tip at one end and a blunt butt end at the other which can be struck by a hammer. A punch as a tool exerts a significant amount of striking force on a very small portion.


Materials
All punches are made from high grade metal alloys like steel, carbon steel, alloy steel, aluminum steel, brass alloys etc . All punches are made to be struck and are, therefore, made of hardened steel. Each type of alloy is hardened and tempered for maximum durability and given different finishes like black oxidized or brown or golden oxidized to give a smooth metallic shine.

Types of punches
There are a wide variety of punches used in engineering and other purposes, but often the basic purpose of a punch is to form the tip on an object or a workpiece. The various types of punches are as follows:

• Prick punch: This type of punch is used make indentations in metals. The shape of the punch is that of a long, tapered punch which is beveled at the tip to form a point. It looks like a center punch but a smaller version. Prick punch is considered to be a light to medium duty tool and typically used to make location marks on an equipment or a work piece. It is primarily used for the purposes of layout. The indentation produced by a prick punch is smaller than a center punch. When layout is complete, the indentation made with the help of a prick punch can be enlarged using a center punch, which allows for drilling. A prick punch's tip when viewed on a profile, has sides at a 30-60 degree angle to one another.
  
  
• Center punch: This type of punch is used to help in drilling operations. They are similar to prick punches but they are bigger, heavier, thicker and suitable for heavy duty work. As such, they are made of specially selected steel, hardened and properly tempered. The points that are used to form indentations on metal surface are ground at a proper angle to give maximum service, and the tips are accurately centered. Center punches give drill bits a true start because if an indentation is not made by a center punch, there is every chance that a drill bit is liable to "walk" across the surface of the work instead of drilling a hole. A center punch's tip when viewed on a profile, has sides at a 90 degree angle to one another.
  
  
• Pin punch: A pin punch is slightly different from a center or prick punches. It is a driving hand tool, used to drive pins. These pins are used to fix a fixture to a rotating shaft. Pin punches have a hexagonal body, with a long, flat ended cylindrical section. They have uniformly narrow shanks which can reach all the way through alignment holes and other circular recesses. Pin punches are available in various sizes and diameters.
  
  
• Drift punch: A drift punch is used in aligning rivet holes/bolts/screws prior to inserting a fastener. It is in the shape of a tapered rod, with the hammer acting on the large end of the taper. The tapered end of a drift punch is put inside the semi-aligned bolt holes of two separate objects, and then driven into the hole. As it is driven inside, the tapered end forces the two components into alignment, which allows for insertion of the fastener easily. Heavy, tapered punches with blunt tips, drift punches help in driving alignment pins out of equipment. They come in a variety of sizes to match the diameters of pins.
  
  
• Hole punch: Their main purpose is to cut circular holes in gasket material, plastics, rubber and even soft metal. They have sharp-edged circular ends instead of pointed or blunt solid tips. The are available in sets consisting of a variety of different size punches for cutting various size holes.
  
  
• Transfer punch: It is of a specific outer diameter that is non-tapered and extends the entire length of the punch leaving aside the tip. A transfer punch's basic purpose is to tightly fit the tolerances of an existing hole and, when the punch is struck, it transfers the center of that hole to another surface. It can be used to copy the hole patterns in a part, or in set locations for threaded holes.
  
  
• Roll pin punch: Roll pin punches have long shafts and large striking heads with hardened points. They are machined specially for removing spring and roll pins. These type of punches are designed to apply consistent pressure to the end of a pin, which help to driving it straight through the hole. The ball centered on the punch tip helps in assuring proper contact, and it removes damage to the pin or hole wall. They are usually hot forged from alloy steel for maximum strength.