Please enable JavaScript.
Coggle requires JavaScript to display documents.
LECTURE 3: GENERAL DRAWING PRINCIPLES - Coggle Diagram
LECTURE 3: GENERAL DRAWING PRINCIPLES
GENERAL RULES
Dimensions must not be repeated
Always in mm unless stated otherwise
An engineering drawing must provide a complete specification for the product
Avoid adding dimensions to hidden detail where possible
Dimensions relating to a design feature are generally placed adjacent to a single view
GEOMETRIC BREAKDOWN
Give dimensions showing the size of the simple geometric shapes (size dimensions) and then also give dimensions describing the location of these shapes (location dimensions)
Exterior = positive and interior = negative
Extension lines / leader lines should not cross dimension lines
Placing dimensions legibly - they should be on the outside of the product or drawing
Do not break extension lines as they cross other line types
Circle with line through proceeds the diameter of circle
CRS - between the centres of holes
DIRECTION OF DIMENSIONS
Chain dimensioning - small errors in each sperate dimension can accumulate to a larger error
Running dimensions - simplified parallel dimensioning using less space
Parallel dimensions - Improved positional accuracy since all the dimensions come from the same datum point
Rectangular coordinate dimensions
DIMENSIONING CURVES, ARCS, RADII AND HOLES
R is for arcs only and shows the size and the arrow must always point at the centre of the arc
Path circle diameter and angles is the dimension that passes through the centre of equally spaced holes
With holes note the depth, but drill point does not need dimensioning