LIMITING LENGTH OF THE OFFSET

The maximum length of the offset is generally determined from the view point that the error produced in plotting the detail on the drawing sheet is not very significant.

• Alternatively, the displacement of the detail on the drawing sheet should not be more than 0.25 mm from its correct position.
• The maximum length of the offset in fact depends on:
• The scale of the plot
• Error in the direction and length of a line
• The desired level of accuracy

Error in the Direction of Offset

Let an offset Pp is taken to the detail P from the running chain line at p. Let there be an error of a in the direction of Pp i.e. the offset makes an angle a with the true perpendicular and let l be the length of the offset.

When the offset is plotted on the drawing sheet, it will be plotted as pP₁ and thus the actual point P gets displaced to P₁. Draw perpendicular PP₂ from P on the line pP₁. Thus displacement along the chain line is PP₂. This displacement is due to the error a and on the drawing sheet, this displacement should not exceed

The Equation can be used for calculating the maximum length of the offset so that maximum displacement on the drawing sheet does not exceed 0.25 mm.

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