City Guilds Model Questions Vol1 2023 Engineering Question 3

A metal part requires a cylindrical hole of diameter \(20\) mm and depth \(50\) mm. Two machining options are considered:\n\n1. Drilling with a twist drill: cutting speed \(30\) m·min\(^{-1}\), feed \(0.15\) mm·rev\(^{-1}\), tool life \(45\) min.\n2. Boring with a single‑point tool: cutting speed \(20\) m·min\(^{-1}\), feed \(0.10\) mm·rev\(^{-1}\), tool life \(60\) min.\n\nThe machine spindle speed cannot exceed \(1500\) rev·min\(^{-1}\). Each tool change takes \(2\) min. For a production run of \(100\) holes, determine which process gives the lower total machining time (including tool changes) and the corresponding total cost if the drilling cost is \(\text{₦}150\) per minute and the boring cost is \(\text{₦}200\) per minute.