steel drill bushings

A drill bushing, also referred to as a jig bushing, may be a tool utilized in metalworking jigs to guide cutting tools, most ordinarily drill bits. Other tools that are commonly utilized in a drill bushing include counterbores, countersinks, and reamers. they're designed to guide, position, and support the cutter .


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.


Types

Drill bushings can generally be 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 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 which will easily get replaced . Press-fit wearing bushings are utilized in short run applications or in applications where the tolerance on a hole location is so tight that it cannot facilitate the utilization of a liner bushing.


Renewable bushings

Renewable bushings are installed in liner bushings. this sort of bushing is employed in large production runs where a bushing will wear out over time or when multiple renewable bushings are utilized in one liner to supply various sized holes. There are two sorts of renewable bushings: fixed and slip.


Fixed renewable bushings are utilized in applications where the liner is supposed to be used until it wears out. Slip renewable bushings are designed to be interchangeable with a given sized liner in order that two different sized slip renewable bushings are often utilized in one liner bushing. This facilitates the power to try to to multiple machining operations that need different inner diameter (ID) bushings, like drilling and reaming. they typically have knurled heads in order that they are often 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 various sorts of locking systems for renewable bushings. One system may be a dog, which may be a collar that's pressed over the top of the bushing and features a long tail. The tail could also be bent at the top so it can lock round the fringe of the jig plate or it's going to be left straight if it can butt up against another object. an alternative choice to stay the renewable bushing from rotating is to pin it, either by putting a pin within the renewable bushing and a hole within the liner or the other way around . A more complicated version uses a hole within the bushing collar and a pin with a head; the top on the pin holds the sting of the collar down, except for removal the bushing are often rotated in order that the opening lines up with the pin.


Specification

Customary bushings are specified using the subsequent 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 that relates to a multiple of a 1⁄64th of an in. (0.40 mm); the length is an integer that relates to a multiple of a 1⁄16th of an in. . The lengths of press-fit bushings are standardized to typical jig plate thicknesses: 5⁄16, 3⁄8, 1⁄2, 3⁄4, 1 , 1 3⁄8, and 1 3⁄4 inch (7.94 mm, 9.53 mm, 12.7 mm, 19.05 mm, 25.4 mm, 34.93 mm and 44.45 mm). The letter "U" is employed after the OD number to designate that extra stock should be left on the OD for grinding to size. the sort may be a letter pertaining to the following:

S - Slip renewable

F - Fixed renewable

L - Headless liner

HL - Head liner

P - Headless press-fit

H - Head press-fit


Custom bushings

A common problem encountered is when two or more holes are too close for independent standard bushings. during this case one large renewable bushing are often made with two (or more) holes within the proper location (the first example within the image). Another possibility is to form a custom bushing with an eccentric hole then notches on the surface of the top are wont to locate the right position of the bushing for every location (the middle example within the image). Another common need for a custom bushing is when the opening needed is perpendicular jig plate; during this case a bracket bushing is employed . it's a hardened piece of right angle steel that screws to the jig plate and is found with dowel pins.