|Chiping - Course: Technique for Manual Working of Materials. Methodical Guide for Instructors|
The following paragraphs comprise proposals on conducting trainee instructions, demonstrations of working techniques, exercises and tests..
Two course variants are recommended:
Variant no. 1
This variant should be chosen for trainees with generally good achievements and receptiveness.
1.1. Introductory instruction for the whole subject, with demonstrations based on the "Trainees' Handbook of Lessons".
1.2. Exercises in chiselling based on the "Instruction Examples 10.1. - 10.5." with subsequent evaluation.
1.3. Final test of theory knowledge based on the "Examples for recapitulation and tests".
Variant no. 2
This variant should be chosen for trainees with little previous knowledge or poor achievements.
2.1. Introductory instruction with demonstrations based on the "Trainees" Handbook of Lessons"
2.2. Exercises in cutting-off chipping based on the "Instruction examples nos. 10.1. - 10.3." with subsequent evaluation.
2.3. Additional instruction in the working technique of chipping chiselling.
2.4. Exercises in cutting-off and chipping chiselling based on the "Instruction examples 10.4. and 10.5." with subsequent evaluation.
2.5. Final test on theory knowledge based on the "Example for recapitulation and tests"
Practical skills should be checked immediately after handing over the finished workpieces. Theory knowledge can be checked constantly; however, it is recommended to have a final test written (item 1.3. to 2.5.) after the exercises.
3.1. Introductory instruction
If possible, this instruction should be conducted in a classroom.
Make sure that the trainees put down necessary and supplementary notes or answers to questions in their "Trainees' Handbook of Lessons".
The instruction can be given based on the main points contained in the "Trainees" Handbook of Lessons".
Purpose of chipping:
The trainees have to learn that cutting-off and chipping by chiselling are energy and time-consuming activities. The instructor has to give examples of such cases where it will not be possible to employ machining techniques and where, therefore, chipping is required.
Based on the transparencies nos. 10.1, and 10.2, the instructor can describe the positions and actions of chisels.
Tools, accessories and protective means for chipping:
The following original tools should be shown and the instructor has to explain when to use them:
- flat chisel (chipping chisel)
- round chisel
- cape chisel
- shear chisel
- grooving chisel
- mortise chisel
- punching tool
If it is not possible to show all the chisels as original tools, transparency no. 10.3. can be used as a teaching aid. The respective illustrations are also contained in the "Trainees' Handbook of Lessons"
When explaining the kinds of chisels the instructor has to mention how chisels are ground.
This includes a description of the relation between the wedge angle of the tool edge and the material properties:
30° - 50°
hard (tool steel)
60° - 70°
Other tools and accessories to be mentioned are:
- locksmith's hammer
- supports (steel plates and blocks, anvil)
The instructor has to stress that surface plates must never be used as a support, because the chisel edge would destroy the surfaces of the plates. The following means of protection should be mentioned:
- protective gratings and screens
- safety goggles and impact protection
Action and working techniques of chipping:
This subject can be clearly explained by using transparencies nos. 10.1. and 10.2. as teaching aids. The instructor has to deal in detail with handling the chisel when chipping and cutting-off. This instruction can be supported by the hints contained in the "Trainees' Handbook of Lessons" and the respective illustrations, as well as by using transparencies nos. 10.4. and 10.5. as teaching aids.
If possible, the instructor has to give a demonstration of chipping and cutting-off chiselling on small-size steel parts. When speaking about cutting-off chiselling of curved contours the instructor has to refer to the preparation of this work by scribing a bore line. He has also to refer to the necessary formulae, and a calculation should be done using the available widths of a double-point punch.
D = diameter of drill
y = width of double-point punch
x = distance of bore line from scribed line
D = y - 0.2 mm
If it has not been possible to include demonstrations in the instructions, this should be done right now prior to the exercises.
Subsequently, the trainees can begin with their first exercises based on the "Instruction examples for practical vocational training".
However, it is necessary to prepare every individual exercise by a brief "job-related instruction" in the course of which the trainees are shown a finished workpiece in order to demonstrate the objectives and purpose of the exercise.
The instructor roust have made such a workpiece himself in order to be familiar with all the problems which might arise from producing such a workpiece.
Thus, the main points of evaluating the achievements can be clearly defined, and the instructor can inform about difficult areas in the exercise. During these instructions the sequences of operations and the working drawings should be placed on the desks so that the trainees can put down additional notes therein.
All the trainees can perform these exercises simultaneously, provided that the necessary tools etc. are available. In this case the trainees can carry out all the individual exercises by themselves. Each trainee should be given as much time as required.
If there are not enough tools available, the instructor has to form groups of trainees. It is recommended to divide these groups on the basis of applying the various kinds of chisels:
group no. 1 - working with flat chisels only
group no. 2 - working with flat, cape and grooving chisels.
If there are still trainees who cannot take part in these exercises, they should perform additional exercises to consolidate working techniques acquired earlier.
3.3. Examples for recapitulation and tests
This section comprises questions which are to consolidate and test the previously acquired knowledge and skills. Each question is provided with the respective answer. Questions which are also contained in the "Trainees' Handbook of Lessons" are marked with the letter "A".
1. What is the purpose of chipping?
(Cutting-off or chipping of material.)
2. When do we employ the chipping technique?
"A" (If it is not possible to employ mechanical techniques or if these are too costly.)
3. What is the material chisels are made of?
"A" (Unalloyed tool steel with hardened cutting edge.)
4. What are the criteria for selecting chisels?
"A" (The criteria are: kind of work and hardness of material-of the workpiece.)
5. What kinds of chisels do we know?
(flat, round, cape, shear, grooving, mortise and punching chisels (tools).)
6. What is the purpose of using flat chisels?
"A" (Flat chisels are the most common tools for cutting-off and chipping chiselling)
7. What is the purpose of using cape chisels?
"A" (They are used for cutting out horizontal grooves and for cutting-off the webs in bore lines.)
8. What is the recommended wedge angle of cutting edges for working on medium-hard steel?
9. Which additional tools and accessories do we need for chipping?
"A" (Hand hammer, supports, vice.)
10. What is the basic principle for selecting the hammer?
"A" (The hammer must have double the weight of the chisel.)
11. Which property must supports have?
"A" (They roust not be hardened so that they can absorb the impact of blows.)
12. Why roust surface plates never be used as supports?
"A" (The penetrating chisel edge would leave notches and uneven spots on the plates so that they could no longer be used for their proper purpose.)
13. What do you have to take into account when chiselling a workpiece in a vice?
(You roust hammer against the fixed jaw of the vice and use a firm counter-support.)
14. Which protective means are used to prevent accidents?
(Protective gratings or screens, goggles and impact protection.)
15. What is the task of protective screens and safety goggles?
"A" (To protect people from being hit by flying chips and fragments of workpieces.)
16. What is the action of chiselling?
(The impact of the hammer on the chisel head is transferred to the cutting edge, which can perform its chipping work now.)
17. What is the position of the chisel in a chipping operation?
"A" (The chisel inclination towards the surface of the workpiece is about 30°.)
18. How are metal sheets chiselled which are clamped in a vice?
(The chisel must be in an inclined position - with an angle of inclination of 45°.)
19. What is the position of the chisel in a cutting-off operation?
"A" (Perpendicular to the surface of the workpiece.)
20. How can we chisel off curved contours from thicker workpiece?
"A" (Scribing and punching of a bore line with a double-point punch; drilling; chiselling off the webs with mortise chisel.)