Marking out

Marking out

1. if the parts are not the right size

   • they will not fit together

2. to make an accurate product, you have to prepare the materials you are going to use

   • measuring and marking out where any machining operations are needed

3. Datum edge

   • provides a set reference point
     • without a flat surface to work from, measurements will not be accurate
   • could also be side, face, from where the dimensions are measured

4. tolerance

   • the amount that a measurement can vary from the stated value and still be acceptable

5. which tool used depends on the required accuracy

   • rule: 0.5 mm tolerance
     • steel or plastic
   • (digital) vernier calipers
     • 0.02 mm
       • sliding section over a steel bar, used to measure thickness or diameter of a part
   • micro-meter
     • 0.1 mm
     • tightens onto a piece of material using a screw mechanism

6. tools for marking out- lines that are to cut or processed on a piece of material

   • wood
     • pencil
       • or a marking knife
   • metal or
     • plastic
       • scriber
         • can be used on very hard tool steel
         • used like a pencil to scratch a mark in the material
         • or ( for metal)
     • punch
       • made form very hard tool steel, which is hit with a hammer to make a mark on the metal
         • dot punch- highlights lines, marks centre of circles
         • centre puch- marks centre of hole to be drilled

7. drawing circles/ arcs

   • for wood: compass
   • for plastic/ metal: dividers
     • similar to compass, but with two hard points, like a scriber, to scratch a line

8. try square

   • if the line is at 90 degrees top edge
   • wooden stock and a carbon steel blade
   • wood and plastic
   • engineer's square
     • same purpose, but for metals
       • metal stock and blade

9. angled lines

   • sliding (or adjustable) bevel

10. complex shapes

    • use a template
      • paper/ card

11. check measurements again, after you have marked out

    • to ensure a mistake hasn't been made before the material becomes waste