BTEB Machinist flashcards

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

Cutting speed formula

V = πDN/1000 gives surface speed in m/min from diameter D in mm and spindle speed N in rpm; it sets tool life and finish.

Feed rate for milling

Table feed f = fz × z × N, where fz is feed per tooth, z is the number of cutter teeth, and N is spindle speed in rpm.

Chip thickness ratio

The ratio of uncut chip thickness to actual chip thickness; it is always less than one because the chip is shorter and thicker than the cut.

Machine guard interlock

A device that prevents the spindle from running while a guard is open and stops the machine if the guard is opened during operation.

Fire class identification

Class A solid fuels, B flammable liquids, C electrical, D combustible metals; the extinguishing medium must match the class to be safe.

Hacksaw blade pitch choice

Use coarse teeth for thick soft sections and fine teeth for thin tube, sheet, and hard alloys so at least three teeth stay in contact.

Filing pressure rule

Pressure is applied on the forward cutting stroke only; the return stroke is light, which keeps the file flat and prolongs tooth life.

Tap drill size

For metric threads the tapping drill diameter is approximately the major diameter minus the pitch, for example 8.5 mm for M10 × 1.5.

Tapping sequence

Start with the taper tap, follow with the plug tap, and finish blind holes with the bottoming tap, reversing a quarter turn to break chips.

Scraping contact check

Marking compound on a surface plate shows high spots; a good bearing surface shows roughly 20 to 25 spots per 25 mm square.

Vernier least count

Least count equals one main scale division minus one vernier division; a 0.02 mm calliper has 49 main divisions equal to 50 vernier divisions.

Vernier calliper reading

Add the main scale value at the vernier zero to the vernier coincidence number multiplied by the least count of the instrument.

Micrometer least count

Least count equals screw pitch divided by thimble divisions; a 0.5 mm pitch with 50 thimble divisions reads 0.01 mm per division.

Clearance fit

A fit in which the smallest hole is larger than the largest shaft, so the parts always assemble with a gap between them.

Interference fit

A fit in which the smallest shaft is larger than the largest hole, so the parts must be pressed or shrunk together.

Hole-basis system

A limit system in which the hole tolerance is fixed and shaft tolerances are varied, allowing fixed-size drills and reamers in production.

Go and No-Go gauges

The Go gauge must pass through or assemble with the full feature; the No-Go gauge must not enter, confirming the limit is not exceeded.

Taper turning angle

The compound rest angle is α = tan⁻¹((D − d)/(2L)), where D and d are the large and small diameters and L is the taper length.

Tailstock set-over

Set-over S = L × (D − d)/(2l), where L is total workpiece length and l is taper length; used for long shallow tapers between centres.

Metric thread depth

For a 60-degree metric thread the depth is about 0.6134 × pitch, so the minor diameter is major diameter minus 1.2268 × pitch.

Four-jaw chuck use

Independent jaws allow irregular, heavy, or eccentric work to be set accurately with a dial indicator, unlike a self-centring three-jaw chuck.

Parting-off conditions

Use low spindle speed, abundant coolant, a tool exactly on centre, and minimum overhang to prevent chatter and tool breakage.

Climb versus conventional milling

Climb milling feeds the cutter with the work travel and improves finish but needs zero backlash; conventional milling is safer on worn machines.

Coolant concentration check

A refractometer measures coolant mix strength; too lean causes corrosion and wear, too rich causes foaming and skin irritation.

Spindle runout check

A dial test indicator on a test mandrel in the spindle taper shows bearing or taper damage when the reading exceeds the maker's limit.

Lathe bed wear pattern

Wear is greatest near the headstock because most cutting happens there; a dial gauge measuring saddle drop along the bed reveals it.

Lockout and tagout

Isolate the energy source, apply a personal lock and tag, and verify zero energy before reaching into a guarded or powered area.

Carbon steel classes

Low carbon is up to about 0.3 percent carbon, medium carbon 0.3 to 0.6 percent, and high carbon 0.6 to 1.4 percent.

Grey cast iron properties

Cast iron with 2 to 4 percent carbon as flake graphite; it machines easily, damps vibration well, and has low tensile strength.

Hardening and tempering

Heat to the austenitising temperature, quench in the specified medium, then temper at a lower temperature to relieve stress and restore toughness.

Machining allowance

Extra stock left for later operations: roughly 0.5 to 1 mm per side for roughing and 0.1 to 0.3 mm per side for finishing.

First-angle projection

On a drawing, the view seen from above is placed below the front view, and the view from the left is placed on the right.