|Scraping of plane surfaces - Course: Technique for Manual Working of Materials. Methodical Guide for Instructors|
The sequence of exercises can follow the order of the 5 exercises mentioned in the Instruction Examples for Practical Vocational Training - Scraping of Plane Surfaces.
These Instruction Examples... also comprise a list of materials (initial material, hand tools, measuring and testing tools, accessories) and a sequence of operations as well as an illustrative working drawing.
Thus, the trainees avail of the necessary information to begin their exercise-related work.
Should the quality of the produced workplaces be considered insufficient, the trainee has to carry out comprehensive preliminary exercises. To do so, any waste parts will do. If the respective skill has been practised sufficiently, the envisaged workpiece can be produced.
The following hint should be taken into consideration:
Scraping can be practised on pre-worked parts. The production of component parts and their assembly can be done by other trainees earlier.
Should the proposed Instruction Examples... not be used in the exercises, then it is also possible to select other work-pieces.
In this case all the working techniques described earlier should be also practised when working these parts.
4.1. Instruction Examples
What follows is a brief description of the individual instruction examples in order to give a survey of those workpieces on which the previously acquired knowledge can be verified:
Instruction Example 6.1. V-block
The trainees will practise the flat-scraping process on a flat steel surface (without given dimensions). Flat scrapers will be employed only.
Instruction Example 6.2. Steel straight-edge
Two parallel, narrow surfaces of flat steel are worked with the flat scraper first and with the pull-type scraper then. After hardening the surface, the straight-edge can be used in the workshop.
Instruction Example 6.3. Try Square
Two or, resp., three narrow surfaces of flat steel are worked in such a way that they are parallel to each other - in accordance with given dimensions. Parallelism will be checked by using dial gauges. After hardening the surfaces, the try square can be used in the workshop.
Instruction Example 6.4. Centre Square
After the production of the components, this device can be used to practise pattern scraping of braiding patterns on steel sheets, After hardening the surfaces this centre square can be used in the workshop.
Instruction Example 6.5. Lathe bed
Planing will be practised at an available lathe bed employing all the necessary techniques of scraping and checking against master plates.
4.2. Criteria for practical training
It is recommended to determine some major points of observation and evaluation of the work to be performed.
The following criteria can serve as a guideline:
- Does the trainee employ long and powerful pushes which run diagonal to the working marks?
- Does the trainee apply the scraper with varying scraper positions?
- Does the trainee exert an increasing pressure?
Checking against master plates
- Does the trainee apply very thin films of the checking ink?
- Does he spread the checking ink evenly over the whole surface?
- Does the trainee recognise the surface appearance, and is he in a position to interpret it?
- Does the trainee apply the flat scraper in short, clearly defined curves?
- Does the trainee persistently work the peaks?
- Does he check regularly?
- Does he achieve the ratio of three peaks to one valley?
Finish-scraping and pattern scraping
- Does the trainee apply the pull-type scraper correctly?
- Is the trainee in a position to produce a regular pattern?