Maharashtra HSC Mechanical Technology (Vocational) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Lathe cutting speed formula

V = πDN/1000, where V is the cutting speed in metres per minute, D is the workpiece diameter in millimetres and N is the spindle speed in revolutions per minute.

Climb milling

The cutter rotates in the same direction as the feed, so chip thickness starts at maximum and falls to zero, giving better finish but requiring a backlash eliminator.

Twist drill point angle

General-purpose twist drills for steel have a 118° point angle and about 30° helix angle; 135° split points are used for hard or stainless steels.

First-angle projection symbol

A truncated cone drawn with its circular view on the right of the trapezium indicates first-angle projection, the method adopted in Indian Standards.

Hole basis fit system

The hole is kept at basic size with zero lower deviation (H); the required clearance or interference is produced by choosing the shaft deviation, such as g, h, k, p or s.

Isometric scale factor

Isometric lengths equal 0.816 times true lengths, drawn along axes at 30° to the horizontal; isometric projection itself uses full true lengths.

Annealing of steel

Steel is heated 30–50 °C above its critical temperature, soaked, then cooled very slowly in the furnace to soften it, refine grains and remove internal stresses.

HSS 18-4-1

High-speed steel containing about 18% tungsten, 4% chromium, 1% vanadium and 0.7% carbon; it retains hardness up to roughly 600 °C, allowing high cutting speeds.

Eutectoid steel

Plain carbon steel with 0.8% carbon that transforms completely to pearlite at 723 °C on slow cooling; it is the eutectoid point of the iron–carbon diagram.

Vernier caliper least count

Least count equals one main scale division minus one vernier division; when 49 main scale millimetres are divided into 50 vernier parts, the least count is 0.02 mm.

Sine bar formula

A sine bar of roller centre distance L, raised by slip gauges of height h, gives the angle from sin θ = h/L; accuracy falls beyond about 45°.

Taylor's principle of gauging

The Go gauge is full-form and checks the maximum material condition of the whole feature; the No-Go gauge checks individual elements at minimum material condition.

Tap drill size

For metric threads the tapping drill diameter equals major diameter minus pitch; M10 × 1.5 needs 8.5 mm and M8 × 1.25 needs 6.8 mm.

File grades

Files are graded rough, bastard, second cut and smooth according to tooth spacing; double-cut files remove metal faster while single-cut files give a smoother surface.

Scraper

A hardened hand tool used after filing to remove high spots from bearing surfaces; the work is marked with Prussian blue and rubbed on a mating surface.

Pattern shrinkage allowance

Patterns are made larger than the casting because metal contracts on solidifying; typical allowances are cast iron 10 mm/m, aluminium 13–16 mm/m and steel 20 mm/m.

Neutral welding flame

An oxy-acetylene flame with roughly equal oxygen and acetylene, giving a well-defined inner cone; it welds mild steel without carburising or oxidising the metal.

Blanking versus piercing

In blanking the punched-out piece is the required product and the remaining sheet is scrap; in piercing the hole is required and the slug is scrap.

Cylinder force formula

F = p × A, where p is the hydraulic pressure and A the effective piston area; the return force is lower because the rod reduces the annular area.

Pneumatic FRL unit

A combination of filter, regulator and lubricator that removes moisture and dirt, sets the working pressure and supplies oil mist to downstream valves and cylinders.

Pressure relief valve

A normally closed valve that opens at a set pressure and returns excess pump flow to the tank, limiting circuit pressure and protecting components from overload.

MTBF and MTTR

MTBF is total operating time divided by the number of failures; MTTR is total repair time divided by repairs; availability equals MTBF divided by (MTBF + MTTR).

Preventive maintenance

Planned servicing carried out on a schedule before failure, including lubrication, adjustment, inspection and replacement of wear parts, to reduce breakdowns and extend machine life.

Bearing code 6205

In the designation 6205, the 6 means a deep-groove ball bearing, 2 the light series and 05 a bore of 5 × 5 = 25 mm.

Class B fire

Fire involving flammable liquids such as petrol, diesel, oil and paint; foam, dry powder or carbon dioxide is used, never a direct water jet.

Lockout tagout

An energy-isolation procedure in which the machine is switched off, the isolator locked and tagged by the person working, stored energy released and zero energy verified.

Noise exposure limit

The permissible exposure limit for an eight-hour shift is 90 dBA; hearing protection is required above 85 dBA, and the level doubles every 3 dB increase.

Break-even point

The output at which total cost equals total revenue, calculated as fixed cost divided by the contribution, that is selling price minus variable cost per unit.

Prime cost

Direct material plus direct labour plus direct expenses; factory, office and selling overheads are added afterwards to obtain the total cost of the product.

Halsey incentive plan

A wage incentive scheme paying a guaranteed time rate plus a bonus of half the time saved, multiplied by the hourly rate of the worker.

Working capital

Funds tied up in raw material, work in progress, finished goods and receivables, less current liabilities; it finances the day-to-day running of the business.

Udyam registration

Free Indian online registration for micro, small and medium enterprises using Aadhaar and PAN, giving access to credit, subsidies and delayed-payment protection.