Types of Drill Jigs and Fixtures | Machine Tools | Engineering

The following points highlight the ten main types of drill jigs. The types are: 1. Template Jig 2. Plate Jigs 3. Plate Fixtures 4. Angle-Plate Jigs and Fixtures 5. Channel Jigs 6. Vise-Jaw Jigs and Fixtures 7. Drilling Fixture 8. Universal Jigs 9. Plastic Jigs 10. Milling Fixture for Milling Rough Casting.

Type # 1. Template Jig:

Plate Drill Jig:

This is the most basic type and the simplest form of drill jig used when only a few parts are to be produced. Template jig can serve as layout guide for locating holes and contours. The drill jig may be clamped to the sheet, in which holes are to be drilled, by means of thumb screws. The plate jig may also be clamped directly to the top of the work by means of C-clamps.

Although template jigs lack the refinements of other types of jigs, they cost much less.

However, templates are not as fool-proof as other types of jigs. Operator has to be careful, otherwise parts could be inaccurately machined.

Types of Template Jigs:

i. Layout Template Jig (Refer Fig. 28.62):

It is used as a rapid reference tool for laying out several identical parts for locating holes, contours, and external part details. The thickness of template material should be sufficient to maintain the proper relationship between template elements.

ii. Flat-Plate Template Jig (Refer Fig. 28.63):

This is used to locate holes on flat surfaces. This template is normally located with pins referenced from the edge or from other holes. The minimum plate thickness is around one to two times the tool diameter.

iii. Circular-Plate Template Jig (Refer Fig. 28.64):

It is used for drilling holes on cylindrical work pieces by locating it on a cylindrical portion of the part.

iv. Nesting Template Jig (Refer Fig. 28.65):

Nesting template jigs usually employ a pin nest to locate work  piece of any form of shape.

Type # 2. Plate Jigs:

Plate jigs are basically modified or improved template jigs. In addition to locating function, it also incorporates a means of securing the part (clamping). The plate generally provides the mounting points for locating, supporting, and clamping the part as well as positioning the drill bushing. Thus the plate jigs locate parts with a high degree of accuracy and repeatability.

i. Plain Plate Jig (Refer Fig. 28.66):

The plain plate jig is the simplest and most basic form of jig. It uses a flat plate as its only structural member to which all the details are attached and referenced.

ii. Table Jig:

The table jig is basically a plain plate jig with legs. It is used for holding irregular or non-symmetrical work pieces. The limitations are with regard to the size of the part and the availability of clamping surfaces. The part is clamped between the jig and the clamping device. The tool thrust is, therefore, directed toward the clamps which must be designed suitably.

iii. Sandwich Jig:

The sandwich jig is like a plain plate jig, with a backup plate, thus permitting to hold very thin parts which would otherwise bend or distort under tool pressure. Sandwich jig can also be used as a combination jig with one side being used to locate the part for drilling and the opposite side for reaming or tapping the part.

iv. Leaf Jig:

The leaf jig (Refer Fig. 28.67) is actually a modification of the sandwich jig. While the sandwich jig uses pins to locate the two members and screws to hold them together, this jig uses a hinge lead with a cam-type latch for the purpose. The part is loaded on the lower section where the locators are normally positioned. The leaf, which carries the bushings, is then lowered and latched.

Type # 3. Plate Fixtures:

It is made from a single base plate on which a variety of details are mounted for locating, supporting, and clamping a part. There is almost on limit to the variety of work which can be performed with plate fixtures.

Type # 4. Angle-Plate Jigs and Fixtures:

These are primarily used to machine parts which cannot be easily machined using plate-type tolling.

The main structural member of an angle tool is an angel which may be structural section or cast-bracket or built up section.

i. Angle Plate Drill Jigs:

These may be made of cast iron or of steel plate. The part is located on one face by a central stud or locating pin and the necessary stops. In the design of angle- plate tool body the vertical member should be either made of same size or smaller than the horizontal member in order to maintain the required rigidity of the tool and to ensure accuracy in the part. If vertical part can’t be made as indicated above then it must be supported by placing gussets or supports between two members.

For drilling holes, bushes are provided on the angle plate. (Refer Fig. 28.68) Plain angle- plate tools are constructed at a 90 degree angle to the machine table and used to machine part details at angles perpendicular to the machine table.

Modified angle plate tools are constructed to suit any angle from parallel to perpendicular to the machine table. Angle plates are also used for designing indexing jigs where it is necessary to drill holes at angular orientation.

ii. Leaf Drill Jigs:

It consists of a grey cast iron body with hardened and ground jig feet inserted in the base. Four hardened and ground rest pins are inserted in the jig body and the job rests on these. A clamp bolt is designed so that it can be pinned into the body of the jig, and a star hand-wheel is used to clamp the leaf of the jig so as to hold the work securely.

A wedge pin with 45 degrees angle at the bottom of leaf clamps works up against the four locating pins in the rear and left portions of the jig. It may be noted that clamping pressure on the work is not applied directly by the leaf spring. The open design of such a jig permits rapid and easy removal of chips and good visibility of work piece.

Type # 5. Channel Jigs:

Channel and box jigs are the detailed types of jigs in common use. These are designed to machine part details on more than one surface without repositioning the work in the tool. These are costly but save a lot of machining time and parts handling time. After loading of part, it is seldom removed until all machining is complete.

The channel jig having its main structural member as channel, is the simplest and most basic form of closed jig, and capable of machining on three surfaces.

Channel jigs provide better stability and support for thin parts in comparison to open jigs. Generally, the work is mounted against the top and one side of the jig while it is clamped from the other side. (Refer Fig. 28.70).

i. Box Drill Jig:

It is normally made in the form of box or framework around a part. It is generally used when it is required to drill holes in two or more sides of a piece. Each side of the jig is brought up under the drill spindle by tumbling a jig.

As this type of jig has to be tumbled to present desired work face to drill spindle it is also known as tumble jig. Feet are provided opposite to each bush plate in box. One side of the box is open for inserting the work and accommodating clamping system.

Box jig also offers good support to frail work piece and excellent tolerance control. When very large holes or very small holes are to be drilled in the same job, it is considered good practice two design two jigs, as small drills will not run efficiently in a drill press that would have capacity to drill bigger holes. While drilling smaller holes in separate jigs, the bigger holes already drilled can be used for location purposes.

ii. Trunion Drill Jigs:

These are heavy box jigs which are moved on trunions to bring the bush face at the top. The jig proper carries trunions at its ends which rotate in east bearing brackets, mounted on a long channel iron. Arrangements are provided to lock it in such a way that the face in which the hole is to be drilled is absolutely horizontal.

iii. Shaft Drill Jigs:

When the production requirements are low then a simple form of drill jig can be employed to drill holes in round shafts. It consists of a solid block in which a hole is drilled throughout of size bigger than the shaft to be drilled.

A stop is provided at the back so that the shaft will be in definite location and on the front a counter sink is provided to facilitate easy insertion of work. A cap screw is provided at top which clamps the job and a drill bushing is inserted in the top portion of the jig. It is also possible to locate the shaft in a V-block in place of a box with circular hole.

iv. Indexing Jigs:

These are used to drill a series of holes in a circle on the face of a work piece. It brings the hole portion under the drill each time it is indexed. Universal index heads used on milling machines are the most accurate in indexing devices but are not suited for mass production as these are likely to lose accuracy under the drilling and milling forces involved. Further these are costly also. The indexing device used for jigs and fixtures should be both rapid in action and positive in location.

Most of the indexing devices are designed on the following principle. The various locating holes, very accurately positioned, are drilled and reamed on an indexing plate or on a cylindrical body. The job is mounted firmly with these and means are provided to rotate the index plate (cylindrical body) along with the job.

A fixed member carries a pivoted spring loaded lever which is lifted for indexing purposes and will seat into the next locating hole only when the job has been indexed to the right position.

An accurate spring loaded indexing device is shown in Fig. 28.72 in which an indexing pin is loaded with a compression spring. The indexing pin is engaged in a slotted plate ; the slots in the plate having one face radial to the centre and second face inclined at 30° to the first face. The working surfaces are hardened and ground. Spring pressure of the order of 30 to 40 kg/cm² is employed for positive action.

Type # 6. Vise-Jaw Jigs and Fixtures:

The Machine Vise:

Vise-jaw jigs and fixtures are the simplest, most basic form, efficient, adaptable, versatile and economical work-holding devices. Machine vise is the basic component used with these jigs and fixtures. Several variations of the machine vise are available to increase the usefulness of this tool.

The usefulness is further increased by use of a special set of jaws for each part. These vise-jaw jigs and fixtures can be used to serve as special work holder for any number of different parts. However use of such vise- jaw jigs and fixtures is limited to parts that can be held into the vise.

The principles for locating the work piece in a vise- jaw tool are same as for other types of jigs and fixtures. The most common method of location work pieces is with pins or blocks; the location being done either by its outside edges or by holes in the part. The parts must always be located against the fixed jaw in order to maintain good repeatability and to prevent any misalignment resulting from the movement of the movable jaw.

The parts which do not have holes or machined edges can sometimes be positioned by using nest-type locators which may be made either by the machining (for symmetrical parts not having intricate details) or by casting methods (for unsymmetrical parts having intricate details). Machined nests are normally used for symmetrical parts which do not have any intricate details. However, their use is restricted to tools used in very long production runs because of their high cost.

For unsymmetrical parts cast nests are used. These are made from plastic, or epoxy resins, or low-melt alloy metals.

Type # 7. Drilling Fixture:

Fig. 28.73 shows a drilling fixture for drilling holes on periphery of the work piece shown by dotted lines in Fig. 28.73. It may be noted that the work piece has a previously machined bore. Help is taken to locate the work piece against this by providing a hardened and ground male spigot in the fixture.

The spider clamp plate is swung up the clamp plate, lowered and the work piece is inserted. It is thus clamped against the spigot shoulder with the spider clamp plate by actuating the cam operated plunger by operating the handle. It may be noted that this method of clamping does not cause any distortion of the work piece.

The twist drill is positioned relative to the work by means of hardened and ground drill bushes which act as guides for the drill. Adequate gap is provided between the bush and work piece so as to avoid it being swarf trap. In order that swarf could easily fall clear through the jig body and slider clamp, adequate clearance is provided.

Jig is made of light construction with high rigidity so that it can be handled easily. It has no sharp corners to hurt operator. The base of jig is so designed that its feet can’t fall into the drilling machine table tee slots. In order that work piece may be placed in the desired position only, fool proof pins can be provided.

Type # 8. Universal Jigs:

Universal jigs are those jigs which are either adjustable, or adaptable to more than one drilling job. Usually the main body and operating mechanism remain same and only top plate (bushing plate) and adapter are changed. In universal jigs the top plate is secured to two vertical posts which can be raised and lowered through a lever arm.

The piece to be drilled is secured on an adapter under the top plate which always remains horizontal and provides clamping pressure. Generally a locking device connected with the lever arm is also provided. The use of universal jigs has the advantages of speed of operation; inter-changeability; and saving in tool cost, design cost and time-study cost.

Type # 9. Plastic Jigs:

Plastic materials are now being used to expedite the production of drill jigs, particularly in aircraft industry. Heavy plastic dies are used for sheet-metal stretching operations and they replace zinc-alloy dies. As these are light in weight, these can be handled more conveniently. If a plastic jig breaks accidently, it can be replaced with little loss of time and with negligible cost. The plastic materials can be ground as tools become obsolete and used over and over again.

The desirable characteristics of plastic materials required to be used for die construction are:

i. It should be easily reclaimable,

ii. It should be possible to machine the plastic jigs with wood working tools,

iii. It should have sufficient impact strength to withstand ordinary shop handling,

iv. It should not become brittle at low temperatures or after aging,

v. It should be resistant to oil metal chips.

The most commonly used plastics for jigs are thermoplastic phenol-acetone resin and acid-setting phenol formaldehyde.

Type # 10. Milling Fixture for Milling Rough Casting:

Fig. 28.76 shows a milling fixture used for milling top surface of cast work piece having no precise locating surface. The work piece is made to rest on four hardened and ground pins having domed tops to provide point contact for uneven cast surface.

Four pins are selected for stability purposes and pins are adjustable type with locking arrangement. Since whole of the top surface has to be machined, cleaning arrangement has to be below the top surface of the work piece.

A serrated fixed jaw is provided on left hand side and a side bridge clamp on right hand side with its serrated edge pulling the work piece firmly down on to the pegs and against the opposite jaw. This arrangement also resists the feed force of milling operation and prevents and possibility of the work piece being pushed out of the fixture due to component of cutting forces in up cut milling.

The fixture is made of heavy, rigid construction to withstand milling cutting forces. Fixture is made of cast iron which also damps the vibration present during the milling operation.

Due to high milling cutting forces, robust clamps with tightening by nut instead of cam arrangement are used. Arrangements for bolting the fixture to the machine table are provided.

Type # 11. Turning Fixture:

Fig. 28.77 shows a turning fixture for the work piece shown in dotted lines in Fig. 28.77. A hole has to be drilled square to the flat face of the fork of work piece. The work piece is located in a horseshoe slot for ease of loading and is also located flat against the location spigot as shown in Fig. 28.77. Latch clamp is used to clamp the work piece through a previously machined slot.

For unclamping the nut is untightened and stud (pivoted at bottom) is pulled down thus permitting quick release. The clamp is so arranged that it will fit through the slot only if the work piece is correctly aligned. The fixture is positioned on the lathe by means of a location spigot at the back of the fixture body which fits the recess is the spindle flange on the lathe.

The location features of the fixture are so arranged that the drill and reamer will be correctly positioned relative to the work piece when they are fitted in the lathe. Complete fixture is balanced by balance weights. Usually a cover, which completely covers the fixture, is provided, for safety reasons.