ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) case studies
ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) · Put your knowledge to work in context.
The All India Trade Test (AITT) is the certification assessment that closes out the NCVT ITI trade course in Mechanic Machine Tool Maintenance. It is aimed at trainees who are finishing institutional training in the trade and must show, in writing, that they understand how machine tools are built, installed, maintained, diagnosed and repaired. The ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) case studies are 5 cases and about 3,370 words.
1Taper and concavity on a newly installed centre lathe
A 2.2 m between-centres centre lathe was installed on a new 150 mm concrete slab, grouted after one week and commissioned without formal levelling. Six weeks later the operator reports that a 300 mm test bar turned between centres measures 0.060 mm larger at the headstock end than at the tailstock end, and facing a 200 mm diameter disc gives 0.030 mm concavity.
904 words, about 5 min2Worm gearbox running hot with the wrong top-up oil
A 15 kW, 1470 rpm squirrel-cage motor drives a single-start worm gearbox through a flexible coupling. The gearbox has a 4.5 litre oil-bath sump and is filled with ISO VG 220 mineral EP oil, splash lubricated, with a shaft-mounted fan.
640 words, about 3 min3Slow approach and drift on a 100-tonne hydraulic press
A 100-tonne double-acting press has a 250 mm bore main ram fed by a variable-displacement axial piston pump rated 63 L/min at 1470 rpm, with a relief valve set at 200 bar. Faults: approach speed has fallen from 8 mm/s to 4.5 mm/s; the ram drifts 5 mm/min when the directional valve is centred and the load is held; the pump-outlet gauge reads 140 bar on the holding stroke although the load needs 175 bar.
643 words, about 3 min4Acceptance decision on a hot batch of Ø25 h7 shafts
A batch of 60 ground shafts, nominal Ø25 h7 (0.000/+0.021 mm), is inspected by a trainee in a room where the thermometer reads 34 °C and there is no air conditioning; the reference temperature is 20 °C. The shafts come straight from the cylindrical grinder, where coolant is at 38 °C, and are measured within two minutes.
586 words, about 3 min5Premature spline pitting on induction-hardened EN19 shafts
A batch of 24 splined drive shafts, 40 mm diameter, is machined from EN19 (AISI 4140) bar, then induction hardened and tempered after spline milling. Specification: surface hardness 55–60 HRC, case depth 1.0–1.5 mm to 50 HRC, core 28–32 HRC, retained austenite below 10 %.
597 words, about 3 min