Assignment # 01

CH # 02: DRILL JIG

TOOL DESIGN

NAME: USMAN AHMED

Roll # 08MR-20

ASSIGNMENT # 01 -----------------------------------------------------------------------------------------------------1) What is a drill jig? A drill jig is a device for ensuring that a hole to be drilled, tapped, or reamed in a work piece will be machined in the proper place. Thus instead of laying out the position of each hole on each work piece with the aid of square, straightedge, scribed and center punch, the operator uses a jig guide the drill into the proper place. In most cases, the work piece is held by the jig, and the jig is arranged so that the work piece can be quickly inserted and as quickly removed after the machining operation is performed. Jigs make it possible to drill, ream, and tap hoes at much greater speeds and with greater accuracy than the holes are produced by conventional hand method.

2) What are the functions of jigs and fixtures? The functions of the jigs and fixtures are as follows, Functions of jigs: - Jigs are used for while drilling, boring, reaming and tapping holes. The skilled workers are not required for these operations, when jigs used. It should locate, clamp and support the work piece, and it should also guide the cutting tool in proper direction. Functions of Fixtures: - Fixture is a production tool, it should be used for milling, planning, shaping, grinding and turning etc. It should hold a work piece during machining operations. A fixture is always fastened to a machine or bench in a fixed position.

3) What is the main difference between jigs and fixtures? The term jig is should use only for the devices employed while drilling, reaming, or tapping holes. It is not fastened to the machine on which it is used and may be moved around on the table of the drilling machine to bring each bushing directly under the drill. Jigs physically limit and control the path of the cutting tool. If the operation includes machining operations like milling, planning, shaping, turning etc., the term fixture should be used. A fixture holds the work piece during machining operation but does not contain special arrangements for guiding the cutting tool, as drill jigs do. A fixture is also fixed to the machine.

4) Why is it poor practice to locate drill bushing in the leaf of a leaf-type drill jig? The disadvantage of the chips may accumulate inside and cause trouble unless provisions are made for them. Also if drill bushings are fitted in the leaf, play in the hinges may affect drilling accuracy. For this reason it is the best practice to locate drill bushing in fixed portion of the jig whenever possible. Often this is not possible, and bushing must be located in the leaf or hinge plate. When this is done, the hinge must be precision-made to ensure alignment and the joints should be constructed of the heat-

treated pins and bushing to prevent excessive wear. The only chance for error is the location of holes relative to the part outline, which may or may not be critical. It is considered poor design to clamp the part with the hinged plate. The hinged plate should close against a fixed stop. When the hinged plate must serve as part of clamping device. In this case hinged plate serves as a support when reaming.

5) What is the advantage of tumble jigs? When a box jig contains bushing on two or more sides for the purpose of the drilling on different sides of the part, it is referred to as a tumble jig. Such a jig has sets of jigs on opposite sides of the work faces. After one face is drilled, the next side may be drilled by simply flopping the jig to expose this side to the drill spindle. The advantage of tumble jigs is that greater accuracy can be obtained and less part handling is necessary.

6) Why should complicated clamping devices be avoided? Complicated clamping devices should be avoided. Many unusual devices are expensive to build and may be a source of trouble. Clamping devices should have a minimum number of loose o moving parts. It requires a great deal of maintenance which may offset the saving of faster operation. A simple clamp with a minimum amount of parts will serve in most cases, so it is better to use standard commercial clamping units whenever possible.

7) Why should the use of loose parts on drill jigs be avoided? Loose parts such as handles, pins, wrenches, gages etc., are another source of trouble in the production shop. They will be lost in spite of all precaution taken by production personal. Whenever possible, a handle of a clamping device should be an integral part of the device. If this is not possible, the handle should be fastened to the jig by a small chain or cable. If the loose part is such that it cannot be fastened to the jig body, it should be marked with proper identification, and some provision for storage should be provided on the body of the jig.

8) Why is chip formation with standard two flute twist drill unlike that of the other metal cutting tool? As a two flute drill passes through a piece of metal is displaced by two pars of the drill point, the drill lips and the chisel of edge of the drill. The cutting process of the drill lips is essentially the same as that of a lathe cutting tool, but at the chisel edge the process is quite different. Here the formation of the metal is much more serves as the chisel edge tends to penetrate the metal and extrudes it outward until it is picked up by the drill lips. The nature of the cutting action at the chisel edge is the reason twist drills require such large axial thrust forces. These drilling forces can be reduced by proper drill grinding, thinning the drill web and grinding special drill points such as crankshaft points, spiral points and prismatic points. After the metal is displaced by the chisel edge and the cutting lips of the drill, it must be ejected from the hole. The drill flutes act as an auger to remove the chips and since there is little room in the flutes, it is desirable to have the chips broken up into small pieces. Long coils tend to pack in the flutes and retard the flow of coolant to the cutting edges. The result is excessive heat and premature drill dulling.

9) What is the advantage of a cast constructed jig body? Cast construction provides a neater jig since the metal may be distributed to better advantages. It may also be easier to cast odd shaped than it is to machine them.

10) What are the three ways chips are removes from drill jigs? Chips are generally removed from jigs in three ways. Coolant will help to flush away chips as they are formed, they may be removed manually with a brush or hook or they may be removed with compressed air. Coolant paths should be provided to aid chip removal by coolant. If chips are to be removed manually with a brush, corners and obstruction should be eliminated to allow the operator to brush out chips with a minimum amount of effort. When compressed air is used, guards should be provided to prevent scattering chips throughout the working area.

USMAN AHMED Roll # 08MR-20