Fig 11 shows a horizontal band saw used in a school workshop to cut lengths of metal bar stock. The blade runs on two large wheels driven by an electric mot...
Question 1 Report
Fig 11 shows a horizontal band saw used in a school workshop to cut lengths of metal bar stock. The blade runs on two large wheels driven by an electric motor. A spring-loaded lever on the frame lowers the blade onto the workpiece during cutting. The cutting speed is controlled through a variable-speed gear mechanism, and an isolation switch on the wall disconnects the entire machine from the mains supply. The fig shows the band saw with the blade guard and material vice clearly visible.
(a) Give one reason why the isolation switch must be turned off before changing the blade on the band saw. [1]
(b) Explain why the lever that lowers the blade is spring-loaded rather than free-moving. [2]
Answer Details
(a) The isolation switch must be turned off before changing the blade because it completely disconnects the machine from the mains electrical supply. [1] This ensures the motor cannot be started accidentally (by someone pressing the start button, or by a fault) while the operator's hands are in contact with the sharp blade. Locking out the power at the isolator is the only way to guarantee the machine is electrically dead during maintenance.
(b) The spring-loaded lever returns the blade automatically to the raised (safe) position when the operator releases the handle. [1] If the lever were free-moving, the blade could drop onto the workpiece or the operator's hands under gravity if the operator let go unexpectedly (for example if startled, or if their grip slipped). The spring provides a fail-safe: the default state of the blade is always raised and away from the cutting zone, and the operator must actively hold the lever down to maintain contact between the blade and the material. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
