both functions (holding the work and guiding a tool) is called a jig. An example of a jig is for a specific operation but does not guide the cutting tool. It provides FOOL PROOF: The design of jigs and fixtures should be such that it would not. Design Tool & Die Use in Industries JJJIG, FIXTURES AND TOOLING This book, in the "Complete Illustrated Guide" format covers jigs and fixtures. Jig and Fixture Design. General Rule-of-Thumb regarding tolerances, the tolerance for the fixture should be roughly 40% . Manual Forces.
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Jig and Fixture Design Manual - Erik K. Hendriksen_ - Ebook download as PDF File .pdf), Text File .txt) or read book online. vfvff f. Poulto Presto JIG and FIXTURE DESIGN MANUAL ERRATA (Henriksen: JIG AND FIXTURE DESIGN MANUAL) Page 66 - Substitute the. is a treatise on the principlesof jig and fixture design which contains . case of drill and boring jigs provided with guide bushings in the same plane, is met with in.
Right Click and Open in a New Window. As mentioned briefly in an article on Welding Jigs and Fixtures, published in section 2 of our Practical Welding Letter Issue for April , PWL , design and fabrication of such tools have a great importance on quality and cost of welding production. In section 3 , PWL , we publish a note of a kind reader on a successful minor change they brought on one of their jigs, as an example of thoughtful improvement. Due to the importance of the subject, readers may find interest in researching sources capable of providing ideas or manufactured items suitable to take part successfully in their production programs. It could be kept handy for reference when required, to get Resources that may be needed in special cases. Welding Problem?
Gandhi and B. Google Scholar 2. Google Scholar 3. Nee, S. Prombanpong and A. Google Scholar 4. Google Scholar 5. Google Scholar 6. Google Scholar 7. Google Scholar 8. Imhof and W. Google Scholar 9. Ingrand and J. Google Scholar Markus, Z. Markusz, J. Farkas and J. Miller and R. Ferreira, B. Kochar, C.
Liu and V. Nnaji, S. Alladin and P. Nnaji and P. Applications outside of this area will be shown by a few characteristic examples. Design and Economy Jigs and fixtures are special tools in the sense that each tool is, generally, designed and built specifically for making one part only and for only one operation on that part.
There are noteworthy exceptions to this general rule. Quite often, drill jigs are built to allow a sequence of operations to be performed at one location, such as drilling followed by tapping or reaming, or drilling to increasingly larger diameters, or drilling followed by countersinking or boring, etc.
Less frequently, a fixture may be designed with interchangeable or adjustable inserts, such that it can be used for several parts of slightly modified shape or dimension. This concept leads logically to the "universal fixture," although "universal" may be an exaggeration.
A universal fixture is constructed from building. After its use is completed, it is disassembled and then reassembled to a new and different configuration. Universal fixtures and jigs of this and other Table Classification of Manual Work Fixtures Ch. They may be less rigid than fixtures of one-piece design but they may,. This is generally not the case, however, with ordinary jigs and fixtures of special design.
Disassembly and reuse of components is ordinarily not economically feasible; thus, when the production is completed, the tooling costs must have been written off, hopefully, with a saving and a profit. Due to the specialized nature of these tools, their designs are as. There are undoubtedly not two identical fixtures in the whole world. The design of these tools is, therefore, a task that challenges the designer's creative imagination and draws heavily upon his experience and ingenuity.
Nevertheless, fixture design is not a task reserved only for geniuses. It is governed by rules, and these rules can be learned, mastered, and practiced by average persons. As evidenced by the structure of this book, that vast variety of possible configurations of fixtures can be subdivided into groups of.
The design process is systematized to an even higher degree. It is governed by a logical, step-by-step procedure that is time tested and leads to a useful end result. It is a cookbook recipe. As such, it supports the beginner, it guides the experienced practitioner, and it may even be of assistance to the expert. Even one. Any mechanical design is incomplete without a documentation of its structural integrity.
The penalty for underdimen-sioning is breakage or warpage of the fixture and is clearly observable. The penalty for over dimensioning of a fixture is "only" excessive weight. The deciding factor. Every design activity must never lose sight of the fact that the purpose of a fixture is economy.
Each design assignment will have a variety of solutions with different degrees of operational economy. They have been selected to represent two characteristic types of fixtures. In addition. The two principal types are shown schematically in Fig. Each of the two sketches shows a part. Typical Examples Before entering upon the detailed discussion of fixture design. The principal difference between the two types lies in the means for obtaining dimensional control.
In the milling fixture Fig. The reason for the need of such guidance is the well-known fact that a drill is a relatively highly flexible tool.
In the drill jig Fig. The fixture shown in Fig. The surface to be machined is the end surface of the short leg of the angle. The total length of the fixture is approximately 18 inches mm. It is a very normal size fixture and can be accommodated on any milling machine except the very small ones. It would. The size and weight of the part to be cut presents no problem.
The fixture body J is a rather solidly designed casting. Once the fixture is positioned on the table it does not have to be moved again and is bolted down. This rest is brought into contact after the actual locating is completed. The extreme left end of the bracket is supported at one point only by means of a sliding rest 5 operated by the plunger 6 and knob 7. The face of the flange was already machined in a previous operation and permits.
A typical milling fixture designed with extensive.
The fixture is aligned to the T-slots in the table by keys 13 and also has. Two straight strap clamps 11 and It should be noted that no spanner or wrench is needed and that a large number of the parts are commercially available.
The main characteristic feature of this fixture is the systematical use of quick-action devices for the application of the supports and the clamping. The lugs are C-shaped for easy insertion of the bolts so that the fixture does not have to be lifted once it has been placed on the table. Planning The complete planning. The Initial Design Concept The design concept is.
As the process goes. They are listed here in their natural sequence. It is not the purpose of this book to. As a general rule. In the design of a drill jig it makes a difference whether the holes are to be drilled before or after machining of the surfaces. Whether the surfaces are rough cast or forged or previously machined makes a radical difference in locating and clamping the part. It is an absolute necessity to have the sequence finalized prior to fixture design.
The requirement is obvious. There exists a set of general rules for selecting the sequence of operations. They are simple and logical. A fundamental rule is that the cutting tool must have ready access to the surface or surfaces to be machined. Rough machining is done before finish machining. These rules are: To allow for natural stress relief. This last rule has.
If the rough part offers good clamping surfaces for the "most severe" operation. In such instances. There may. This is accomplished by choosing the direction of the feed so that the cutter enters the material from an already machined surface.
This rule is quite general and can be applied to parts with combinations of machined outside surfaces and holes or slots. Another equally important consideration is the avoidance of broken edges in castings and burrs on ductile parts. If holes were drilled and slots were milled first. The rule can be stated in its generality as follows: Surface machining comes before depth machining. Examples of such lists are given in Tables through Four areas of information must be taken into account.
At this and other design phases. Such lists may appear trivial.
Table Material Class 1. Material Type 2. Material Properties 3. Part Configuration. Special Components of Part Configuration 5. Machining 1. Table is self2. From the material properties he can select the grade of tool material to be used and form a first opinion on the size and type of fixture required.
Stake Tab-bend Assemble with a sea O-ring gasket flow-sealer Other 3. Fixtures for other non-cutting operations 4. As the specific operation. Equipment for Manual Work Opera tion g 2. Foundry equipment sand preparation equipment molding machines core making machines. Surface coating equipment plating tanks painting booths drying and baking ovens. Joining Equipment 3. One more aspect should certainly be considered.
Table brings the designer closer to many details. Table has been prepared. Each bit of information within this accumulation has some bearing one way or another on some point within the developing fixture concept. As the result of this development process the preliminary fixture design emerges. To assist in pinpointing the individual subjects within the whole and sometimes quite complicated fixture structure. Speed considerations 1.
Miscellaneous 4. Safety of work 2. Operator considerations 3. General Considerations in Fixture Design 1. Loading and unloading of part 1. Support of part 4. Positioning cutting tool relative to loaded fixture 5.
Chips 7. Coolant supply and return 7. A graphical presentation of. It may be found desirable to look for alternate solutions before the final decision is made. Methods for such economic considerations will be discussed further in Chapter This examination involves a very large number of details.
It has been found useful to establish a check list for items of this type. The items are listed in their logical sequence. It also permits the reader to make such additions as his special conditions may require.
Those mentioned first are those which are most likely to be overlooked during the initial planning stages. A check list is the book in a nutshell and has two uses: Some items are listed in more than one place.
Check List for Fixture Design No list can cover all conditions in every company and plant. It is not supposed to be memorized. Execution of Shop Drawings Pha Fig. Outline of the fixture planning process. The Part Drawing 1. Check List 1. It should be applied systematically. Z The Shop 2. It is advisable to check whether it is located properly for the present purpose.
The Machine Tool.
Inspect the condition of the table. Also check T-slots relative to holes or slots in the fixture clamping lugs. Check dimensions of machine tool table.
Check overall dimensions and the space within which the fixture is to be installed the tooling area. The fixture must be fully supported and must not overhang the edge or end of the table.
For rotating fixtures such as on lathe spindles. Make sure that the machine is strong and rigid enough to carry the weight of the fixture and absorb shocks and vibrations from the operation. The machine must be capable of performing the required table traverses and other motions with the fixture. With fixture in place. Make sure that breakage of tool. In such cases.
On multiple-spindle machines. Beware of screw heads. The jig. When one jig is used on a multiplespindle machine and moved from spindle to spindle.
Cutters 4. The operator or setup man must be able to check the correct setting by visual observation. Make sure that the cutter cannot be damaged by contacting the fixture. Preferably it should not be necessary for the operator to have his hands close to the cutter. Check for other interferences when. A case in point is drilling with multiplespindle drill heads and with the drills on different levels.
The fixture should be designed for minimum length of cutter travel. A whipping tendency can be eliminated by providing a bushing at a high level.
The location of this bushing must be high enough to allow the jig to be unloaded and reloaded while the drill is running. In the case of drill jigs. If the jig is heavy. A light jig will be moved to correct position by the elasticity of the drill. A slender drill may enter the drill bushing even if the jig is slightly off position.
Mark fixture accordingly. Cutter Setting other than by drill bushings 5. Carefully select setting block material hardened steel. They should always be kept in stock. Very soft part material. The Part 6.
Hard and abrasive part material may require carbide faced locating and supporting elements.
Very thin-walled. Clamps may be provided with leather. Clamps may be hand-operated with knurled head screws to prevent application of excessive torque.
In case of serious locating problems. Look for mismatched castings. Look for flash on forgings. In drill jigs of simple type. Locating the Part Rough Parts 7. Criteria for evaluation of such items are static stability and compatibility with.
They should be hardened. If a fourth or more point is needed for stability. The basic condition is that their tolerances must be fine enough for the accuracy required in the following operations. Locating pins for eounterbores.
If locating from two drilled holes. Make them of unequal length foi easy catch. In the case of a light operation.
Provide clearance at the base of all locating pins. It may be light. Clamping 9. The cutting forces should act to hold the part in position. Supporting and clamping points should be selected as-wide apart as possible. The part should be supported directly below the clamping points with solid metal inbetween. There are a few special cases where it is correct to.
Do not rely on friction to resist the cutting force. Note again that these cases are few and special. This must be prevented by providing adequate support points.
The cutting forces should not act to upset. Check force and stress analysis to make sure that the fixture and the clamps. The cutting and clamping forces should not act to distort the part or the fixture. For milling fixtures. Make sure that clamps cannot be loosened accidentally by centrifugal forces. All forces from clamping must be retained inside the structure of the fixture.
They must not generate strain in the machine tool structure even if excessive clamping force is applied. Hydraulic clamp. Mechanized clamp. Check all provisions that facilitate the clamping operation.
Have at clamps accessible from one side operator's side of fixture. Use compression springs under straps to hold them up when the bolt is unscrewed. Use stops to prevent ro-. Avoid loose pieces. On large and heavy clamping straps.. Use toggle clamps for quick action. One hand clamps while the other hand engages the feed lever. Look for two-hand operations. Allow plenty of room for the operator's hands.
Check clearance relative to the fixture walls. Locating points should be clearly visible. Heavy parts should be located end for end. Loading and Unloading Provide sufficient clearance for the part in alt positions during loading and unloading.
Make them as short and as small as possible. Use the diamond-shaped cross section. Make ends of pins pointed and rounded for easy catch. With two locating pins.
Combine movable jacks. Knurled handles. Place all operational devices on operator's side of the fixture. Allow for burrs from previous operations. Fixtures may be built with duplicate space for parts so that one space is unloaded and reloaded. Many operations. The finished part is ejected by inserting the new part.
Drill Bushings Wherever possible. If the press fit fails. All straight bushings should be checked for this eventuality and if such displacement can be harmful. Cut end of bushings with a plane cut. Accurate work requires bushings to be carried near the surface of the part. Slip bushings may be omitted by using a stepped drill for drilling and counter-boring in one operation.
Check to see that liner bushings aie hardened. Let the large diameter enter the bushing before cutting starts. A hinged bushing plate can also replace slip bushings. Flanges should be large and fluted preferable to knurled for easy gripping.
Slip bushings should be marked "drill" or "ream. They should be effectively locked in place. The drill jig should be marked with drill size adjacent to bushings. Small jigs may be provided. The choice depends on size and weight of the jig. In other cases. Drill Jigs Space the feet so that all cutting forces act inside the feet. Index pins must move in and out easily. This motion may be facilitated by providing rockers cradle fashion.
Fixtures in General Provide brackets or other means for mounting them. Precision locating from previously bored holes may require expanding plugs to eliminate effect of diameter tolerances.
Fixture may be designed with adjustment devices to compensate for machine tool misalignment. Boring fixtures may advantageously use hall-bearing mounted pilot bushings for small-diameter boring bars running at high speed. Establish the chip type that is produced when machining the part. The Chips Avoid forming corners and pockets that can collect chips. Provide openings. Pilot ends on tools should have grooves or flutes for chips.
V-blocks and other locators with reentrant surfaces should have clearance for chips and burrs. Lift surfaces of locators and supports above possible chip accumulations. Cutting fluid may be directed so as to assist in chip removal.
Keep such surfaces small in area and provide for cleaning. If necessary. Protect movable parts such as plungers. Keep area of feet small narrow. Chips on table may jeopardize position if they get under fixture feet.
Protect rotating machine parts from entangling long chips. Be reluctant to use compressed air. Nonintegral feet should have press fit or be fastened by screws from the top. Cutting Fluid Provide necessary holes for this purpose.
Safety Take a last and critical look at the'dimensions of the cutter. Inspection of Pan Provide visibility of measured surfaces and measuring instruments. Beware of the following two cases: This calls for close cooperation both in the design of the fixture and of the inspection device. This applies not only to drill bushings. Be certain that replacements can be.
Make sure of access to the "inner end" of parts with a press fit. Do not forget tool identification number. Provide breathing holes on bores for.
Do not forget countersinks where desirable. Support surfaces. Avoid blind holes. Avoid square and polygonal holes for plungers and similar moving parts.
Sufficient mass to absorb shock and vibration. Provision for alignment of precision press-fitted precision parts. Dowel pins. The process of fixture design differs drastically from the design process usually applied to a machine part. The loads are then applied. Steps in the Fixture Design Process. The conventional method of machine design consists.
In the practical design process. The sequence is locating. In fixture design. A "small" particle a point. It can move in any direction. Locating and Degrees of Freedom Locating the part is. The six degrees of freedom can be made up by. If these three motion components are arrested. A "body" consisting of several. These three points prevent motion in the vertical direction and also prevent rotation.
Locate the bottom surface on three points not in a straight line see Fig. As a simple and fully realistic example. In other words.
The block can stiU slide in two directions in the plane defined by the! This prevents motion in the crosswise direction and also rotation around the vertical axes. Now add see Fig. It has one degree of freedom left. Locating Principles. The addition of a fourth point at the bottom surface see Fig. Using the Clamping Elements. Application of three points on the bottom surface. To apply six individual locating points.
Application of four points on the bottom surface. In actual fixture design. The principle of locating a part by single locating points. For example. The hold-down forces referred to above were imaginary forces. In actual design. The number of clamping elements used are not necessarily equal to the number of locating points. One important rule at this point is that a clamping force must be applied as directly as possible.
In case the block in Fig. This is. Tang, J. Zhang, R. Dong and M. Gandhi, B. Thompson and D. CrossRef Google Scholar Woodward and D. Wright, E. Kurokawa and M. Thompson and M. Review,39 9 , pp. Lee and L. Markus, Z. Markusz, J. Farkas and J. Miller and R. Englert and P.