Engineering Drawing and Workshop Calculation
What this domain tests
Engineering Drawing and Workshop Calculation checks whether you can read and produce first-angle orthographic views, apply dimensioning and limit-fit notation, and do the arithmetic that supports a workshop job: cutting speed, spindle rpm, machining time, taper, and simple areas and volumes. The drawing half rewards precision; the calculation half rewards unit discipline.
Core rules
- Indian workshop practice follows first-angle projection. Know the standard first-angle symbol and never mix first-angle and third-angle placement on the same sheet.
- Show visible edges as continuous thick lines, hidden edges as short-dashed lines, centre lines as long-short chain lines, and hatching at 45° in section views.
- A limit and fit is written as basic size followed by tolerance classes, e.g. 25 H7/g6: capital letter = hole, lower-case = shaft; H7/g6 is a clearance fit.
- Cutting speed: v = πDN/1000, with D in mm, v in m/min, N in rev/min. Machining time for a lathe pass: T = (L + approach)/(f × N), with feed f in mm/rev.
Worked example
A 50 mm diameter mild-steel bar is turned with HSS at 25 m/min. Find the spindle speed. N = 1000v/(πD) = 1000 × 25/(3.142 × 50) = 159 rev/min. If the turned length is 120 mm and feed 0.2 mm/rev, time = 120/(0.2 × 159) = 3.77 min, before adding approach and retract.
Traps
Mixing first- and third-angle placement; treating diameter as radius; forgetting to convert mm to m in v = πDN/1000; using feed per minute instead of feed per revolution; quoting a tolerance without its basic size.