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Scales

From DT Online

Diagonal Scale


Description

A Scale can be used if a full-size (or true-size) drawing would be too big to fit on the paper being used or where drawing at larger than full-size is useful to show greater detail (e.g. when designing a circuit board). They can also be used to convert units of measurement (e.g. objects measured in inches drawn full-size, but in millimetres on the drawing).


Drawing at full-size is said to be drawn at a ratio of 1 : 1 (i.e. 1 unit in reality is drawn as 1 unit on paper). For a drawing to be half-size 1 unit in reality would be equal to ½ size units on paper, so would have a ratio of 1 : 2, quarter-size would be 1 : 4 and so on. The ratios are derived from a Representative Fraction which is given as:


RepresentativeFraction.png


Features and Applications
Plain Scale
  • Start by deciding how many units long the scale needs to be (e.g. the longest dimension on the drawing).
  • Draw a line to represent this length to scale (e.g. half actual size)
  • From one end, a second line at an angle to it.
  • Step off along this second line equal divisions of any convenient size up to the number of units required.
  • Join the end of the last division to the end of the first line and draw lines parallel to it through all other divisions as shown.
  • Sub-divide the first scale division as required using a similar procedure and start numbering the scale from the end of this.

PlaneScale.png
Diagonal Scale
  • It is not practical to create very small sub-divisions on Plain Scale, hence the need for a Diagonal Scale.
  • Begin by creating a Plain Scale as above but draw a rectangle equal to the length of scale and any convenient height.
  • Create the major sub-divisions as before (e.g. ¼, ½, ¾, or cm, etc.) and extend the divisions vertically.
  • Divide the height of the rectangle into as many minor sub-divisions as are needed (e.g. ⅛,⅜,⅝,⅞ or mm, etc.) and draw horizontal lines through the points.
  • Draw diagonals to each of the vertical rectangles created by extending the sub-divisions.
  • Half way up, a diagonal would cross the rectangle at half its width and so on, thus providing the minor sub-divisions (see the example measurement shown of 3.450 metres).

DiagonalScale.png

Note: There are occasions when drawing accurately to scale can provide more than a good representation, or model, of the finished product. Scale drawings can be measured from and used to transfer sizes of a complex shape on to a large sheet of material for example, but in general and with the advent of CAD, measuring off an Engineering Drawing is not as common as it once was - and has never been satisfactory for really accurate work.


DT Online Buyers' Guide
Helix Oxford Maths Set - Tin B43000 Linex Student Saver Bundle Helix Precision Plus Drawing Set A33002 Primary Shape Template Set Linex Circle Template with Tangential Squares Protractor and 45 1mm-36mm Circles 260x130mm Ref LXG1217T Helix National Curriculum Drawing Set Key Stage 3 & 4 Mathematics Geometry Helix 3 Piece Stencil Set / Letters Numbers and Symbols 10mm 20mm 30mm H90100 Linex Universal Architects Template with Room Furniture and Electrical Symbols Tinted Green Ref LXG1259S 3 French Curve Transparent Templates Stencils Helix T30000 Oxford 30-inch Acrylic Edged T-Square
Helix Oxford Maths Set - Tin B43000 Linex Student Saver Bundle Helix Precision Plus Drawing Set A33002 Primary Shape Template Set Linex Circle Template with Tangential Squares Protractor and 45 1mm-36mm Circles 260x130mm Ref LXG1217T Helix National Curriculum Drawing Set Key Stage 3 & 4 Mathematics Geometry Helix 3 Piece Stencil Set / Letters Numbers and Symbols 10mm 20mm 30mm H90100 Linex Universal Architects Template with Room Furniture and Electrical Symbols Tinted Green Ref LXG1259S 3 French Curve Transparent Templates Stencils Helix T30000 Oxford 30-inch Acrylic Edged T-Square