The trainees who have completed the course are supposed to have a good command of the techniques of making pinned joints. To achieve this, the following is required:
Objectives of training
- The trainees will have a ready knowledge of the purpose and the types of pinned joints and the stresses in pinned joints.
- The trainees will master the various techniques of making joints by use of fitting cylindrical or taper pins.
- The trainees are in a position to select the right type of pin for a particular joint.
- They select the right type of tool and aids and use them in the proper way. They keep strictly to all safety regulations.
To meet these objectives, the instructor or teacher should emphasize the following points of content:
Subject matters of training
· Purpose and types of pins and pinned joints
· Stresses in pinned joints
· Types of tools and auxiliary accessories, fields of their application
· The technological steps of fitting cylindrical and taper pins, grooved pins and dowel pins
· Undoing pinned joints
· Labour safety regulations
· Preparing the component parts for assembly
· Assembling the component parts and inserting the pins
· Checking the component parts prior to and after assembly
· Undoing pinned joints
All instructions, demonstrations and exercises should be prepared thoroughly and meticulously.
2.1. Planning the Practical Vocational Training in the Techniques of Making Pinned Joints
Draw up a time schedule and set an approximate number of hours in which you expect to complete the instruction on the various techniques of making pinned joints. Plan an appropriate number of hours for the theory instruction on each subject, the practical demonstration, the instruction in the preparation of a particular job, especially the exercises, the proper execution of the exercises, for repetitions and checks.
When planning your time schedule, remember the level of know-how of your trainees, the conditions of training, the jobs which your trainees will take on in future and the degree of difficulty of the respective training stage.
The emphasis at each stage of training is always on the impartment of high craftsmanship and teaching of mechanical skills with the help of practice-related exercises which should be given the biggest chunk of time in your schedule.
2.2. Preparing Labour Safety Instructions
A short labour safety instruction should precede every practical exercise, where the main points of the safe handling of all tools, auxiliaries, etc. are explained to avoid injuries. The directions which are binding on the safe handling of drills, countersinks and reamers should be repeated as they apply to the techniques of pinning. The following focal points should be repeated several times:
- Make sure that all tools are clean, sharp and undamaged.
- Use hammers, drifts, punches, etc. which are in good condition.
- Make sure that the workpiece is clamped securely and safely. Never apply excessive force. This may damage the workpieces.
- Put all measuring and testing means aside at their proper places. Use pads, supports, etc. where provided, to protect them against impact, shock and corrosion.
- Drive in pins only when the component parts are securely clamped and cannot slip.
- It is regarded as good workmanship to keep one's workplace tidy and always to put down individual components together with their matching parts.
Have a notebook or file at hand where you keep minutes of these instructions. All trainees shall certify with their signature that they were instructed accordingly.
2.3. Preparing the Teaching Aids
- Each trainee should have a copy of the Trainees' Handbook of Lessons-Pinned Joints.
- Prepare surveys and tables which you can write at the blackboard prior to theory struction periods.
- Make available a sufficient number of pins, pinned joints, as well as samples or functional assemblies with pinned joints for demonstration.
2.4. Preparing the Working Materials
- Each trainee should have a copy of the Instruction Examples... -Pinned Joints for theoretical reading.
- Make sure that a sufficient number of tools, measuring and testing means and auxiliary accessories are available as specified in the Instruction Examples.... -Pinned Joints.
- Check that there is a sufficient supply of tools, measuring and testing means and auxiliary accessories for the practical exercises at hand.
- The following is recommended as a basic stock:
· Marking gauges, steel scribers, centre punches
· Locksmith's hammers, light metal hammers, drifts, punches
· Vernier callipers, plug limit gauges, try squares
· Drills, cylindrical and taper reamers, countersinks, triangular scrapers
· Cutting fluid, machine grease, tap wrenches
· Vices with protected jaws, specific clamping devices
- A bench-type or column-type drilling machine and the required work-holding devices are needed for preliminary operations (drilling, boring, countersinking).
- Check the safe and reliable operation of these machines before your trainees use them.
The following paragraphs make suggestions for the theory instructions, demonstrations of the techniques of making pinned joints as well as for checking and assessing the trainees' knewly acquired know-how.
3.1. Introductory Instruction
The trainees should be instructed on the basics of the subject. For this, use a room where they can sit down and take notes. The trainees should be asked to enter the answers to the questions in the Trainees' Handbook. The trainees are supposed to have a good command of the techniques of boring, drilling and reaming before they are instructed on the techniques of making pinned joints. The essentials of these techniques should be repealed occasionally.
The contents of the Trainees' Handbook follow the system of the introductory demonstration and instructions. The focal points in that Handbook can be discussed in the order given there.
Purpose and types of pins and pinned joints
To start with, explain to your trainees the advantages of joining parts with pins. Use visual aids to demonstrate the mechanical details and functions of the different kinds of pinned joints. This way, jour trainees will understand the difference of pinned joints used. Discuss with them the various kinds of joints and their applications. Explain the designations of all pins to enable them to identify the nominal diameter of a pin in order to select the right size of drill for making a hole. Where no pins or pinned joints are available, use the Figures in the Trainees' Handbook to make your trainees familiar with them.
Stresses in pinned joints
Make frequent use of the blackboard to explain the stresses in pinned joints. Your trainees must understand that a positive connection in a properly pinned joint can only be achieved if the preworked bore holes are of the right size and match the diameter of the pin. Use a drawing on the blackboard to discuss, in addition to friction, the shearing stress in pinned joints, which can be so strong that the pins shear off.
Tools and auxiliary accessories
Introduce the tools and auxiliary accessories, and their applications. Your trainees will have some knowledge from their instructions on the manual techniques of material working. Discuss these points again with your trainees. Ask them questions to find out what they remember. Repeat the details of the following tools:
- Drills, countersinks, reamers
- Locksmith's hammers, light metal hammers
- Non-ferrous metal punches, drifts
- Clamping devices, supports, pads.
Technological process of making pinned joints
Pinned joints, generally, are made by using two different technological methods. It is recommended to explain and illustrate the differences in these methods. Joints which use cylindrical pins or taper pins typically involve the operation of reaming. Ask your trainees as many questions as you think are needed to make sure that they remember the details of this technique. Refer to the Trainees' Handbook, where the technique is described and the formulae are given for calculating bore hole and countersink dimensions. Use practical exercises to illustrate your explanations. Ask several trainees to demonstrate the calculations at the blackboard. Be very particular about pointing out the details of fitting taper pins. Emphasize the importance of using taper pins of the right length.
Joints which use grooved pins or dowel pins need not be reamed. The technological operations for these joints can be explained with reference to the points using cylindrical or taper pins.
Undoing pinned joints
There are essential differences in undoing pinned joints, depending on whether the hole is a through hole or a blind hole. Discuss these differences with your trainees. The loosening and dismantling of pinned joints is a most requisite procedure. However, the fact must be stressed and explained several times that seized pins and pins in blind holes must be removed with a drill. This is in most striking contrast to what the trainees were told about the specifics of pinned joints. It is a major point to make them understand that some way out of a given situation must always be found, even if it involves destroying the pin. It is more important not to damage the component parts of the joints. The trainees should be told that this is a rule, and follow it.
Safety at work
The main points of safe boring, drilling, countersinking and reaming should be discussed once more. These main points can be taken from the Trainees' Handbook of Lessons.
Instruct your trainees to observe all safety regulations. This should be done before the practical exercises are begun. Then show every trainee his place of work and check that the machines and other pieces of equipment in the workshop are in good condition.
Begin each exercise by explaining the theoretical background and follow it with the practical performance of the exercise. Tell your trainees to go about their work with a sense of good craftsmanship.
Also tell them where to expect difficulties. The practical exercises can be done in the sequence in which they are given in the Instruction Examples..... Using the Instruction Examples .... - Pinned Joints your trainees can do four exercises in different techniques. The Instruction Examples.... contain a list of materials for each exercise, tools, measuring and testing means, auxiliary accessories, the details of the technological operations and a workshop drawing.
The trainees will find there the information they need to execute the exercises properly and thoroughly. The instructor is advised to make the trainees aware of weak spots, where there may be difficulties and enable them to correctly assess the results of their work.
The instructor will do good to previously do the exercises himself. To make the instructor more aware of the points which his trainees are to achieve in their practical training, we will describe now the instruction examples for practical vocational training.
Instruction Examples 32.1.: Making a Pinned Joint for Fastening
Two square bars are to be joined successively by using a grooved cylindrical pin, a taper pin and a cylindrical pin. Check each pin for tight fit. Undo the joint. Then fasten a suitable piece of sheet metal to the square bar by means of a grooved drive stud (round head) and a grooved drive stud (countersunk).
Instruction Example 32.2.: Making a Support Plate
Grooved pins are inserted according to half length reserve taper grooved dowel pins into specific locations on a 10 mm steel plate. Another piece of plate is to be located on the first, which serves as a support. The shape and the size of the second plate can be varied by the instructor.
Instruction Example 32.3.: Making a Swivel Joint
A simple swivel joint is to be made from flat steel pieces and pins. One and is made pivotable by a cylindrical pin with a loose force fit. A fixed joint is produced at the other end using a grooved cylindrical pin. The joint is to be secured against torsion by a grooved taper pin.
Instruction Example 32.4.: Making a Container with Lid
A container is to be made from 8 mm plate metal. The plates are held together by grooved taper pins. The lid is removably connected to the body by close-tolerance grooved pins.
All trainees can do the exercises together if sufficient numbers of component parts are available. This will give every trainee a chance of doing all exercises himself. Allow the trainees as much time as they need to complete the exercises. If not enough component parts, tools, etc. are available, the trainees can work in groups. Each group should practise the use of a particular type of pin. Other exercises can be done instead of those suggested above. In that case the instructor should make sure that the techniques taught in this course can be practised extensively.
Major points as to practical training
It is advisable for the instructor to select certain aspects which he will give his particular attention when supervising and evaluating the trainees' exercises. Here are a few suggestions:
- Do the trainees prepare their workplaces with sufficient care and circumspection?
- Do they select the appropriate types and sizes of tools for the exercise they want to do?
- Will they do the job in the correct sequence of operations?
- Do they grease the pins before inserting them?
- Are the trainees able to meet the quality requirements?
· Do the pins fit the holes exactly and tightly?
· Are the heads of the pins flush with the surface of the work-piece (except pins for holding)?
· Do the pins serve the intended purpose in a joint?
- Are the trainees able to assess their own work correctly?
- Have all labour safety regulations been observed?
3.3. Recapitulation and Checks
A list of questions has been compiled for this paragraph. They are intended to check the trainees' know-how. A question is followed by the correct answer in brackets. The letter Q indicates that the question has already been asked in the Trainees' Handbook.....
1. What are pinned joints?
Q (Pinned joints are disconnectable joints, whereby two or more individual parts are held together by pins. Several different types of such connections are known.)
2. Name the main types of pins.
Q (Cylindrical pins, taper pins, grooved pins, dowel pins)
3. How are pinned joints specified?
Q (Pinned joints are specified as to the function of the pin in the joint.)
4. What types of pinned joints are produced?
Q (Pinned joints for fastening, driving, holding, swivelling, fitting, securing and shearing.)
5. What is typical of a pinned joint for fastening?
Q (Pinned joints for fastening hold together two or more component parts without frictional connection.)
6. What is typical of pinned joints for holding?
(One component part is held at another component part by a pin.)
7. What is typical of a pinned joint for swivelling?
(The component parts of the joint are movably or swivably connected with one another.)
8. What is typical of a pinned joint for fitting?
Q (The component parts of this joint are fixed in a definite position relative to one another.)
9. What is typical of a pinned joint for securing?
(The component parts of this joint are protected against becoming loose accidentally under dynamic loads.)
10. What is typical of a pinned joint for shearing?
(Pinned joints of this type secure their component parts, which are connected directly with each other, from overloads. The pin will break when the load becomes too heavy.)
11. Identify stresses which the pin in a joint is exposed to.
Q (Frictional forces between the walls of the bore hole and the surface of the pin, external forces that act on a component part of the joint, shearing stresses by the parts of the joint.)
12. Name important tools and accessories for making pinned joints.
Q (Locksmith's hammers, light metal hammers, non-ferrous metal punches and drifts, drills, countersinks, reamers, clamping devices and supports.)
13. What is the sequence of operations when making a joint by using a cylindrical pin?
(Setting up and clamping the component parts, drilling, countersinking, reaming, checking, cleaning the hole, pinning.)
14. What holes will you drill for a cylinder pin having a diameter of 26 mm?
Q (Rough-drill a 24 mm diameter hole and countersink it to 25.8 mm diameter.)
15. How will you produce bore hole for taper pins?
Q (Use a drill of the nominal diameter of the taper pin. Large holes are made stepwise.)
16. What is the taper per unit length of taper pins and what does it mean?
(A taper per unit length of 1:50 means that the diameter is reduced by 1 mm for every 50 mm of length)
17. What type of countersink will you use to deburr a bore hole?
Q (Use a 90-degree included angle countersink.)
18. What should be taken into consideration when reaming a taper pin joint?
Q (When reaming a hole for a taper pin joint, test the fit of the pin before you drive it in.)
19. What condition must be satisfied with respect to the length of a taper pin?
Q (The length of the taper pin must be 2 mm shorter than the thickness of all parts of the proposed joint.)
20. How will you shorten the length of a taper pin?
Q (Saw off the thicker end of the pin with the hacksaw and file a new head.)
21. How do you insert a pin?
(Drive the pin in with an aluminium hammer or a locksmith's hammer and a non-ferrous metal punch. Proceed from the end at which you applied the reamer.)
22. How should a pin fit its hole?
Q (The upper edge of the pin must be flush with the edge of the bore. More specifically, both ends of a cylindrical pin must be flush with the edge of the bore. Taper pins, on the other hand, have their thicker end flush, the thin end is 2 mm inside the hole.)
23. What are the differences in the technological operations when producing a joint by using a grooved pin or a cylindrical or a taper pin?
Q (The bore hole for the grooved pin is made in accordance with the nominal diameter of the pin. Bores for cylindrical pins must be reamed, those for grooved pins need not be reamed.)
24. How can you remove a pin from a through hole?
Q (Apply several blows on a drift of a nominal diameter somewhat thinner than that of the pin. Apply the drift to that end of the pin which is opposite to the driving-in end.)
25. How can you remove a drive stud?
(Apply a flat chisel sideways between the head of the grooved pin and the surface of the component part and slightly lift the drive stud by a few blows with a hammer. Remove it with a pair of longs.)
26. How can you remove seized pins?
(They have to be removed with a drill.)
Use visual aids to reinforce the trainees' understanding of your instructions. Such aids can be pins, pinned joints or components or assemblies of machines with pinned joints. Instructors are advised to use sample joints made by the trainees during their practical exercises and demonstrate good and bad joints.