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After having completed the vocational training, the trainees shall master the techniques for manufacturing feather key joints.
For this purpose, the following aims must be reached:
Aims
- The trainees have thorough knowledge of the purpose and kinds of and stress on feather key joints.- They master the various techniques used for manufacturing fitting key and sliding key joints.
- They are able to choose the suitable fastening devices according to the function of the respective feather key joint.
- The trainees are able to choose the right tools and auxiliary means and to use them according to the regulations on health and labour safety and fire protection.
In order to achieve these aims, the following contents must be imparted by the instructor:
Contents
Knowledge
- Purpose of feather key joints, kinds of feather key and profile shafts as well as kinds of feather key joints- Stress on feather key joints
- Kinds and fields of application of tools, devices and auxiliary means
- Technological processes for manufacturing feather key joints and profile shaft joints
- Detachment of feather key joints
- Labour safety
Abilities
- Preparation of the parts for assembly
- Assembling the parts and putting the feather keys in
- Checking the parts before, during and after assembly
- Detachment of feather key joints
In order to ensure that the instructions, exercises and demonstrations go off smoothly, the instructions must be carefully prepared.
This includes the following measures.
2.1. Planning of the Training in Techniques for Manufacturing Feather Key Joints
Starting from the total number of teaching hours, the individual sections of this lesson should be planned separately.
Time planning is recommended for the following sections:
- Introduction into the techniques in the form of an instruction.
- Required demonstrations.
- Task-related instruction in preparation of the exercises.
- Carrying out of the exercises.
- Recapitulation and tests.
With the planing of the time, following factors should also be considered:
- The level of education of the trainees;
- The conditions of training;
- The future field of working of the trainees;
- The difficulties the respective section may offer.
The focal point of each section of training is the acquisition of skills by practical exercises, which, therefore, must be given the major portion of time.
2.2. Preparation of the Instruction on Labour Safety
Before the beginning of the exercises, a brief instruction is held on the appropriate use of the working means and on accident-free working.
The same hints are applicable which have to be observed with filling, scraping, drilling, reaming, milling and shaping. Special attention has to be paid to the following points:
- Use only clean, undamaged and sharp tools.- Clamp the tools firmly and safely - but so that they are not damaged.
- Measuring and testing tools must be kept carefully and protected against damage due to shock and corrosion.
- The workshop place has to be kept in order, individually manufactured elements of a component are kept only together with their counterpart.
The trainees confirm the instruction on the above points by their signatures in a book especially started for this purpose.
2.3. Preparation of the Teaching Aids
- The “Trainees' Handbook of Lessons - Feather Key Joints” is distributed according to the number of trainees.- Surveys and especially meaningful illustrations from the “Trainees' Handbook of Lessons” may be prepared as blockboard drawings before the lessons.
- Various feather keys, different feather key joints as well as models or serviceable components may be used as illustrative material, as far as they are available.
2.4. Preparation of the Working Means
- As a theoretical basis of the exercises that have to be done, the “Instruction Examples for Practical Vocational Training - Feather Key Joints” are distributed among the trainees.
- The materials which are required for the exercises must be prepared and placed at the disposal in sufficient quantity according to the enumeration in the “Instruction Examples for Practical Vocational Training”.- The workshop has to be inspected as to the complete supply of tools, devices, measuring and testing tools and auxiliary equipment corresponding to the planned exercises.
- Recommended basic equipment:
· Steel scriber, centre punch
· Locksmith's hammer, light metal hammer, non-ferrous metal drift pins
· Finishing files, triangular scrapers
· Vernier caliper, dial gauge and stand, external limit gauges, plug limit gauges
· Drills, countersinking cutters, thread taps, reamers, tap wrenches
· Screw drivers, adjustable pliers, pliers for shaft snap rings in various sizes
· Cutting oil, machine grease, soluble oil emulsion
· Vice with protective jaws, special clamping mens
· Hand screw press, pullers.
- For the necessary preparatory work - drilling and countersinking - a bench-type or upright drilling machine with the corresponding clamping means is required.- The serviceability of this machine is to be tested before the beginning of the exercises and taking into consideration the regulations on health and safety at work.
The following sections contain suggestions for the structuring of the instructions, the demonstrations of the techniques as well as of the exercises and tests.
3.1. The Introductory Instruction
If possible, the introductory instruction should be held with the trainees in a classroom. During the instruction pay attention that the trainees write down supplements or answers of questions in the “Trainees' Handbook of Lessons”.
An essential presupposition for manufacturing the various kinds of feather key joints is also the knowledge and mastering of the techniques of manual working and machining of material. This knowledge should be reactivated when the opportunity arises. The instruction can be held according to the focal points indicated in the “Trainees' Handbook of Lessons”.
Purpose of feather key joints, kinds of feather keys and profile shafts as well as kinds of feather key joints
In the form of a lecture the trainees are explained what is understood by feather key joints, what tasks the feather key joints have to fulfill and what are the advantages and disadvantages of feather key joints.
It is recommendable to explain different kinds of feather key joints on the basis of the available illustrative material; in this context, also the differentes in the use of the various feather keys can be demonstrated.
The various feather keys should be shown and their special fields of use be explained.
After this, it should be pointed to the manufacture of the joints by profile shafts. It should be emphasized that these joints follow the principle of feather key joints, although no additional connecting elements are used.
The trainees should understand that this kind of joints is especially used for highly stressed machine parts.
Stress on the feather key joints
This is best explained with the help of a blackboard drawing according to Figure 9 from the “Trainees' Handbook of Lessons”. The trainees should understand that the positively connected joint is only stressed when the rotating movement starts and that the power transmission is only enabled by the exact fit of feather key and keyway. By the blackboard drawing the trainees are explained the acting forces and the shearing stresses to be derived thereform.
Tools, devices and auxiliary means
Starting from the knowledge in the fields of manual working and machining of material, these working means are presented in connection with their fields of use.
This focal point should be developed in the form of a talk with the trainees, the instructor testing the level of knowledge of the trainees by systematic questions.
The following working means must be mentioned:
- Shank cutters and side milling cutters
- Internal broaches and keyway cutting tools
- Files and scrapers
- Presses and screwing fixtures
- Hammers and non-ferrous metal drift pins
- Pliers and screw drivers
- Pullers (extractors)
Technological processes for manufacturing feather key joints and profile shaft joints
Since the steps of work with the manufacture of the various kinds oft feather key joints differ only slightly, it is recommendable to describe in detail the manufacture of one commenly used fitting key joint. In the “Trainees' Handbook of Lessons”, this sequence of operations is described in great detail by 8 partial steps. This should be follow by a supplementary explanation of the sliding key and profile shaft joints. For the considation of already imparted knowledge it is important that the trainees realize the relation of cause and effect. This can be achieved by constantly drawing their attention to the consequences which an omitted or wrong step of work may have for the serviceability of the feather key joint. In doing so, the instructor may point to the development of qualities such as accuracy, conscientiousness and perseverance in working.
Detachment of feather key joints
The detachment of feather key joints must be explained to the trainees by two essential steps. One thing is to explain how shaft and hub can be separated.
Starting from their knowledge, the trainees should answer the question how very tight interference fits between shaft and hub can be detached. The methods suggested by the trainees my be discussed, then the correct suggestions are confirmed and/or supplemented by the instructor. In conclusion, the individual steps for removing the keys out of the keyways of the shafts are explained.
Hints on health and safety at work
While repeating the instructions on health and safety at work from the fields of manual working and machining of material, special points are emphasized which are especially applicable in the present field. These focal points are to be found in the “Trainees' Handbook of Lessons”.
3.2. Exercises
On principle, the necessary instructions on labour safety must be given before beginning the exercises. Then, the workshop places are allocated to the trainees and the technical equipment of the workshop is checked as to its serviceability. It is recommendable to begin every exercise by a demonstration by the instructor in connection with explanations related to the respective instruction example. In doing so, the trainees are motivated to carry out the exercise in a good quality. In this context, the focal points for assessment are mentioned and it is pointed to problems to be expected with the respective workpieces for exercise.
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The instructor must have manufactured the workpiece which is the subject of the exercise himself before! |
The exercises can be done in succession in the order of the instruction examples offered.
According to the “Instruction Examples for Practical Vocational Training - Feather Key Joints” - 4 exercises in different techniques can be carried out. The material “Instruction Examples for Practical Vocational Training” gives a list of the required initial material, working tools, measuring and testing tools and auxiliary means as well as the sequence of operations for doing the exercises and a clear working drawing. Thus, the trainees are provided with all required information for implementing the exercises systematically. The initial materials must be prefabricated by machines before beginning the exercises. It is necessary that the shafts and hubs are available true to size in accordance with the dimensions indicated in the working drawing, otherwise the individual operations belonging to the exercise cannot be observed correctly. If no feather keys from standardized assortments are available, these must be manufactured too. The corresponding dimensions are to be found in the working drawing.
In order to give a survey by what exercises the imparted knowledge shall be put into practice, the individual instruction examples are briefly described below.
Instruction examples
Instruction example 34.1. Fitting key joints I
A hub is to be connected with a shaft by a round-end flat key as a fitting key. The axial displacement of the hub is prevented by two shaft snap rings.
(Figure 1)
Instruction example 34.2. Fitting key joint II
A hub is to be connected with a stepped shaft by a Woodruff key as a fitting key. The axial displacement of the hub is prevented by one shaft snap ring.
(Figure 2)
Instruction example 34.3. Sliding key joint I
A hub is to be slidably mounted on a shaft using a straight-ended flat key, which is to be fixed in an ending key way of the shaft by locking screws.
(Figure 3)
Instruction example 34.4. Sliding key joint II
A hub is to be slidably mounted on a shaft using a round-ended flat key, which to be fixed in a closed keyway of the shaft.
(Figure 4)
After having fulfilled these tasks, the trainees detach the joints. All trainees can carry out the exercises at a time, if materials and tools can be provided in sufficient quantity. In this case, the trainees can do the exercises individually - each trainee shall take the time he needs.
If not enough working means are at the disposal, tasks and trainees are divided into groups. It is recommendable to proceed according to the field of use of the various feather keys. If the instruction examples offered are not used for any exercise, other pieces for the purpose of exercise may be chosen. In doing so, pay attention that all the techniques that had been discussed previously can be practised by these pieces for exercise.
Criteria in practical exercise
It is recommendable to fix criteria for assessing the exercises. These can be the following:
- Do the trainees prepare their workshop places carefully?
- Are the appropriate tools - size and form - chosen for the assembly?
- Do the trainees observe the correct order of the individual steps of work?
- Do the trainees slightly grease the parts before assembling them?
- Do the trainees fulfill the quality standards of work?
· Do the feather keys exactly fit in the keyways?
· Are shaft and hub exactly assembled corresponding to the given fits?
- Are the joints detached in the correct way?
- Are the trainees able to judge their own work correctly?
- Do the trainees observe the regulations on health and safety?
3.3. Examples for Recapitulation and Tests
For consolidating and testing the acquired knowledge and skills, this section contains questions which are also included in the “Trainees' Handbook of Lessons”.
1. What are feather key joints?
(Detachable joints where
parts that shall do rotating movements are positively connected.)
2. What are the special advantages of feather key
joints?
(Guarantee of true running of the parts, stability of the joints
even with higher rotary powers.)
3. What is the disadvantage of feather key joints?
(They
do not stand often changing shock-like stress.)
4. What kinds of feather keys are distinguished?
(Flat
keys and Woodruff keys)
5. What kinds of feather key joints are
distinguished?
(Fitting key joints, sliding key joints, profile shaft
joints.)
6. What kind of stress is a feather key in a joint exposed to
during the transmission of power?
(- Surface pressing between the side
faces and the machine parts;
- Shearing stress due to opposite forces
applied.)
7. What technique is used for making the keyways in the
shafts?
(Milling)
8. What techniques are used for making the keyways in the
hubs?
(Broaching or shaping.)
9. What techniques are used for reworking of feather
keys?
(Filing, scraping)
10. What are the criteria for checking the individual parts, if
a fitting key joints shall be made?
(Surface quality of shaft and bore
hole in the hub; length, width, depth and alignment of the keyway of the shaft
and of the hub, fit size of shaft and hub.)
11. How tight must be the fit of feather key in the keyway of
the shaft?
(The lateral surfaces of the key must perfectly fit to the
keyway of the shaft; there can be a slight interference fit.)
12. How can a hub be placed on the shaft, if there is an
interference fit between the two parts?
(The hub is shoved on the shaft in
hot condition.)
13. What are criteria for checking after a fitting key joint has
been made?
(Clearance between feather key back surface and keyway of the
hub, firm fit of hub and shaft, firm fit of the fitting key, fit of the hub in
the right place on the shaft, exact true running of the hub on the shaft.)
14. How can the axial displacement of the hubs on the shaft be
prevented?
(Shaft snap rings or retainer rings are mounted on the left and
on the right sides of the hubs.)
15. What enables the firm fit of the sliding key in the keyway
of the shaft?
(The sliding key is fixed by locking screws in the keyway of
the shaft.)
16. What kind of fit is required between shaft and hub with a
sliding key joint?
(Easily sliding clearance fit.)
17. How is a fitting key joint detached, if there is an
interference fit between shaft and hub?
(The parts are drawn apart by an
appropriate pulling device; if the fit is too tight, the hub must be heated for
a short time, then, the fitting key is lifted out with the help of adjustable
pliers.)
In order to facilitate the understanding on the part of the trainees, it is recommendable to use illustrative objects. These may be individual parts of components or machines, which include feather key joints. Also, work-pieces from exercises held before - according to the “Instruction Examples 1 to 4” - may be included in the instruction to show well made or inferior feather key joints.
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