TOOLS AND TECHNIQUES - MARKING OUT ON PLASTICS Flashcards
What do sheets of plastic normally have lightly stuck to their surfaces?
A thin layer of protective film or paper or polythene
What is the name for a flat face and straight edge surface from which you should always mark out on plastic, unless an irregular shape is being cut out?
The DATUM surfaces and are places where you should always start measuring.
Why should you leave the protective film on plastic for as long as possible?
To prevent scratches
If the protective film on the sheet of plastic is paper, what can use it for?
Marking out
What are the 2 main methods for marking out on plastic?
- Marking out on a paper covering
2. Marking out directly on the surface
How would you mark out on a paper covering?
- If the protective film is already removed, stick a piece of paper on the surface with Pritt Stick, diluted PVA glue or with Copydex
- Then mark out on the paper with using a sharp pencil or fine liner
What tool would you use to mark out lines at 90 degrees to an edge on a paper covering
A woodworking or engineer’s try square which is also used to ensure that one edge is at 90 degrees to the other
What can be used to mark out circles on a paper covering
Pencil compasses
What advantage does the paper covering method have?
It ensures that the easy-to-scratch surfaces are always protected
How would you mark out an irregular shape?
Cut out the paper covering in the form of a TEMPLATE and glue this onto the surface for cutting around.
What would you use to glue on the template?
Pritt Stick or diluted PVA glue
What would you use for marking out directly on the surface of plastic?
A chinagraph pencil or a fine spirit felt-tip pen because it can be easily removed if a mistake occurs.
How would you mark out lines at 90 degrees directly on the surface of plastic?
With a woodworking or engineer’s try square and a chinagraph pencil. You can use an ordinary compass and a chinagraph pencil to mark out a circle.
What would you use to mark out very accurate work on the surface of plastic?
A scriber for marking out lines and engineer’s dividers for marking circles. These should not be used to make deep scratches.
What must you always remember when working with plastic?
Even light scratches cannot be easily remove or polished out of a plastic surface.
