COREN Craftsman flashcards

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

Tapping drill size

For a metric thread, subtract the pitch from the major diameter: M10 × 1.5 needs an 8.5 mm drill. Too small a hole risks tap breakage; too large gives shallow threads.

Cutting speed formula

V = πDN/1000 relates cutting speed V in m/min, diameter D in mm and spindle speed N in rpm. Rearranged, N = 1000V/(πD) gives the required rpm.

Draw filing purpose

The file is held at both ends and drawn along the workpiece. This removes fine amounts of metal and produces a flatter, smoother surface than cross filing.

Arc length in welding

Keep the arc length roughly equal to the electrode core diameter. A long arc causes spatter, undercut and shallow penetration; too short an arc causes sticking.

Clearance versus interference fit

A clearance fit always leaves a gap between shaft and hole. An interference fit always overlaps, requiring force or heat, while a transition fit may give either.

Datum surface in marking out

A proven flat or square reference face from which all other dimensions are measured. Establishing it first prevents accumulated error across the workpiece.

First-angle projection layout

The object lies between observer and plane, so the front view sits below the top view and the left-side view appears on the right of the front view.

Third-angle projection layout

The plane lies between observer and object, so the top view sits above the front view and the right-side view appears on the right. Common in US drawings.

Hidden detail line convention

Hidden edges are drawn as short evenly spaced dashes of equal length. They are omitted where a dimension or centre line would make the view unreadable.

Drawing scale calculation

Scale equals drawing length divided by actual length. At 1:50, a 10 m wall measures 200 mm on paper, since 10 000 mm divided by 50 is 200 mm.

Limit dimension interpretation

A size written 25 +0.05/−0.02 permits a maximum of 25.05 mm and a minimum of 24.98 mm. The tolerance band is the difference, 0.07 mm.

Section hatching convention

Cut material is shown by thin lines at 45 degrees. Adjacent components are hatched in opposite directions so their boundaries remain distinguishable in assembly sections.

Surface roughness Ra

Ra is the arithmetic mean deviation of the profile in micrometres. A lower Ra value indicates a smoother surface, and the symbol is placed on the finished face.

Carbon steel classification

Low carbon steel holds up to about 0.3% carbon, medium 0.3 to 0.6%, and high carbon 0.6 to 1.4%. Rising carbon raises hardness and tensile strength while reducing ductility.

Stress and strain definitions

Stress is force divided by cross-sectional area, in newtons per square millimetre. Strain is change in length divided by original length and is dimensionless.

Annealing versus normalising

Annealing softens metal and relieves internal stress by slow furnace cooling. Normalising refines grain size by cooling in still air, giving better strength and machinability.

Quenching and tempering sequence

Quenching cools steel rapidly to form hard martensite, which is brittle. Tempering reheats it to a lower temperature to restore toughness while retaining hardness.

Grey cast iron properties

With roughly 2 to 4% carbon as graphite flakes, grey iron is brittle in tension but strong in compression and damps vibration well, suiting machine bases and housings.

Galvanic corrosion mechanism

When two dissimilar metals contact in an electrolyte, the less noble metal becomes the anode and corrodes preferentially. Insulating the joint reduces the effect.

Micrometer least count

Least count equals screw pitch divided by thimble divisions. A 0.5 mm pitch with 50 thimble divisions reads to 0.01 mm on the thimble scale.

Vernier calliper least count

Least count equals the smallest main-scale division divided by the number of vernier divisions. A 1 mm main scale with 50 vernier divisions reads to 0.02 mm.

Zero error correction

If an instrument does not read zero when fully closed, its error is added to or subtracted from every reading, depending on whether the error is negative or positive.

Dial test indicator use

The indicator measures small displacements, run-out and alignment rather than absolute size. Its plunger contacts the work and the needle shows deviation from a set zero.

Hacksaw blade tooth selection

Use 14 to 18 teeth per inch for thick solid sections and 24 to 32 for thin tube and sheet. At least two teeth should contact the work at any time.

Grinding wheel marking meaning

The marking gives abrasive type, grit size, grade and bond. A softer grade is chosen for hard materials so dulled grit is released and the wheel stays free-cutting.

Torque wrench accuracy range

A torque wrench is most accurate in the middle of its range. Using it below roughly 20% of full scale gives unreliable torque, so the range must cover the target value.

COREN mandate

The Council for the Regulation of Engineering in Nigeria registers engineers, technologists and technicians, sets standards and disciplines registrants for professional misconduct under the Engineers Act.

Unregistered practice offence

Practising engineering or using the protected title engineer in Nigeria without COREN registration is an offence under the Act and can lead to prosecution and penalties.

COREN code of conduct duties

Registrants must work only within their competence, avoid misrepresenting qualifications, keep client information confidential and disclose any conflict of interest promptly.

Hierarchy of hazard control

Hazards are addressed by elimination, substitution, engineering controls, administrative controls, then personal protective equipment, which is the last line of defence.

Permit-to-work system

A formal written authorisation for high-risk tasks such as hot work, confined-space entry or electrical isolation, recording precautions, isolations and the authorised persons before work starts.

Lock-out tag-out purpose

Isolating and locking energy sources before maintenance prevents unexpected start-up or release of stored energy, protecting workers servicing machinery or electrical equipment.