Drill bushing
Encyclopedia
A drill bushing, also known as a jig bushing, is a tool
used in metalworking
jig
s to guide cutting tool
s, most commonly drill bit
s. Other tools that are commonly used in a drill bushing include counterbore
s, countersink
s, and reamer
s. They are designed to guide, position, and support the cutting tool.
In the USA, Customary sized bushings are standardized via ASME B94.33 and metric
bushings are standardized via ASME B94.33.1. There are over 50,000 standard configurations of customary sized bushings.
Fixed renewable bushings are used in applications where the liner is meant to be used until it wears out. Slip renewable bushings are designed to be interchangeable
with a given sized liner so that two different sized slip renewable bushings can be used in one liner bushing. This facilitates the ability to do multiple machining
operations that require different inner diameter (ID) bushings, such as drilling and reaming. They usually have knurled heads so they can be easily removed.
Renewable bushings must be secured in their liner bushing, otherwise the tool can cause it to spin, which rapidly wears out the liner, or chips can force the bushing out of the liner. There are many different types of locking systems for renewable bushings. One system is a dog, which is a collar that is pressed over the head of the bushing and has a long tail. The tail may be bent at the end so it can lock around the edge of the jig plate or it may be left straight if it can butt up against another object. Another option to keep the renewable bushing from rotating is to pin it, either by putting a pin in the renewable bushing and a hole in the liner or vice versa. A more complicated version uses a hole in the bushing collar and a pin with a head; the head on the pin holds the edge of the collar down, but for removal the bushing can be rotated so that the hole lines up with the pin.
Where the ID is specified as a decimal, drill letter size, drill number size, or fraction; the OD is an integer
that relates to a multiple of a th of an inch; the length is an integer that relates to a multiple of a th of an inch. The lengths of press-fit bushings are standardized to typical jig plate thicknesses: , , , , 1, 1 , and 1 inch. The letter "U" is used after the OD number to designate the that extra stock should be left on the OD for grinding
to size. The type is a letter referring to the following:
The following two tables give the tolerances for the ID and OD.
hole and then notches on the outside of the head are used to locate the proper position of the bushing for each location (the middle example in the image). Another common need for a custom bushing is when the hole needed is perpendicular jig plate; in this case a bracket bushing is used. It is a hardened piece of right angle steel that bolts to the jig plate and is located with dowel pins.
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...
used in metalworking
Metalworking
Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewelry. It therefore includes a correspondingly wide range of skills,...
jig
Jig (tool)
In metalworking and woodworking, a jig is a type of tool used to control the location and/or motion of another tool. A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. A jig is often confused with a fixture; a fixture holds the...
s to guide cutting tool
Cutting tool
In the context of machining, a cutting tool is any tool that is used to remove material from the workpiece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, plaining and similar operations, and remove...
s, most commonly drill bit
Drill bit
Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....
s. Other tools that are commonly used in a drill bushing include counterbore
Counterbore
A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole, or the tool used to create that feature. A spot face is a very shallow counterbore...
s, countersink
Countersink
A countersink is a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common usage is to allow the head of a countersunk bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material...
s, and reamer
Reamer
A reamer is a metalworking tool used to create an accurate sized hole. The process is called reaming. They may be used as a hand tool or in a machine tool, such as a milling machine or drill press.-Construction:...
s. They are designed to guide, position, and support the cutting tool.
In the USA, Customary sized bushings are standardized via ASME B94.33 and metric
Metric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...
bushings are standardized via ASME B94.33.1. There are over 50,000 standard configurations of customary sized bushings.
Types
Drill bushings can generally classified as: press fit bushings or renewable bushings. Other classification methods include by head type, by use, and by liner type (or lack thereof).Press-fit bushings
Press fit bushings are available in two types with liners or without (wearing bushings). Liner bushings, sometimes called master bushings, are permanently installed into the jig and accept liners that can easily be replaced. Press-fit wearing bushings are used in short run applications or in applications where the tolerance on a hole location is so tight that it cannot facilitate the use of a liner bushing.Renewable bushings
Renewable bushings are installed in liner bushings. This type of bushing is used in large production runs where a bushing will wear out over time or when multiple renewable bushings are used in one liner to provide various sized holes. There are two types of renewable bushings: fixed and slip.Fixed renewable bushings are used in applications where the liner is meant to be used until it wears out. Slip renewable bushings are designed to be interchangeable
Interchangeable parts
Interchangeable parts are parts that are, for practical purposes, identical. They are made to specifications that ensure that they are so nearly identical that they will fit into any device of the same type. One such part can freely replace another, without any custom fitting...
with a given sized liner so that two different sized slip renewable bushings can be used in one liner bushing. This facilitates the ability to do multiple 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...
operations that require different inner diameter (ID) bushings, such as drilling and reaming. They usually have knurled heads so they can be easily removed.
Renewable bushings must be secured in their liner bushing, otherwise the tool can cause it to spin, which rapidly wears out the liner, or chips can force the bushing out of the liner. There are many different types of locking systems for renewable bushings. One system is a dog, which is a collar that is pressed over the head of the bushing and has a long tail. The tail may be bent at the end so it can lock around the edge of the jig plate or it may be left straight if it can butt up against another object. Another option to keep the renewable bushing from rotating is to pin it, either by putting a pin in the renewable bushing and a hole in the liner or vice versa. A more complicated version uses a hole in the bushing collar and a pin with a head; the head on the pin holds the edge of the collar down, but for removal the bushing can be rotated so that the hole lines up with the pin.
Specification
Customary bushings are specified using the following specification layout:- ID-Type-OD-Length
Where the ID is specified as a decimal, drill letter size, drill number size, or fraction; the OD is an integer
Integer
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...
that relates to a multiple of a th of an inch; the length is an integer that relates to a multiple of a th of an inch. The lengths of press-fit bushings are standardized to typical jig plate thicknesses: , , , , 1, 1 , and 1 inch. The letter "U" is used after the OD number to designate the that extra stock should be left on the OD for grinding
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
to size. The type is a letter referring to the following:
- S - Slip renewable
- F - Fixed renewable
- L - Headless liner
- HL - Head liner
- P - Headless press-fit
- H - Head press-fit
The following two tables give the tolerances for the ID and OD.
| Nominal ID [in] | Maximum [in] | Minimum [in] |
|---|---|---|
| 0–0.25, including | +0.0004 | +0.0001 |
| 0.25–0.75, incl. | +0.0005 | +0.0001 |
| 0.75–1.5, incl. | +0.0006 | +0.0002 |
| Greater than 1.5 | +0.0007 | +0.0003 |
| Nominal OD [in] | Maximum [in] | Minimum [in] |
|---|---|---|
| – | +0.005 | +0.010 |
| & | +0.010 | +0.015 |
| Greater than | +0.015 | +0.020 |
Custom bushings
A common problem encountered is when two or more holes are too close for independent standard bushings. In this case one large renewable bushing can be made with two (or more) holes in the proper location (the first example in the image). Another possibility is to make a custom bushing with an eccentricEccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
hole and then notches on the outside of the head are used to locate the proper position of the bushing for each location (the middle example in the image). Another common need for a custom bushing is when the hole needed is perpendicular jig plate; in this case a bracket bushing is used. It is a hardened piece of right angle steel that bolts to the jig plate and is located with dowel pins.