COREN Craftsman common mistakes
COREN Craftsman · Understand the traps and how to avoid them.
Answering questions about limits, fits and tolerances by recalling a remembered rule of thumb instead of computing the allowance and reading the designation (e.g. treating H7/h6 as interchangeable with H7/g6, or calling a clearance fit an interference fit).
Candidates memorise a handful of shaft/hole designations and never practise reading tolerance tables. Under time pressure they pattern-match the letters and pick whichever designation looks familiar, ignoring that the fundamental deviation letter and the IT grade together determine the fit type.
What to do instead
Work through 20–30 fit problems by hand: for each pair, subtract the shaft limits from the hole limits to get maximum and minimum clearance (or interference), then classify the fit. Build a one-page table of the common hole-basis fits (H7/g6 sliding, H7/h6 locational clearance, H7/k6 transition, H7/p6 interference) and rehearse classifying them from numbers, not letters.
Describing workshop processes (marking out, filing, drilling, tapping, turning, welding) in vague generalities rather than sequencing the operations and naming the tools and parameters used at each step.
Many candidates have hands-on experience but have never written a process down. They answer from muscle memory, so they omit critical steps such as centre-punching before drilling, using the correct tap drill size, or clamping direction - and lose marks on questions that ask for order of operations or tool selection.
What to do instead
For each core process, write a numbered step list with the tool named at every step and the key parameter (tap drill diameter = major diameter minus pitch; drilling speed from cutting speed and diameter; filing stroke and file type). Practise producing these sequences from memory in under five minutes each.
Misreading orthographic projections - treating a first-angle drawing as third-angle (or vice versa), placing a plan view above rather than below the front view, or failing to transfer heights correctly from the front view to the side view.
Candidates learn one convention in school or on the job and assume it is universal. Nigerian practice and most teaching use first-angle projection, but textbooks and imported drawings often show third-angle symbols, and candidates do not check the projection symbol before interpreting the views.
What to do instead
Always locate and state the projection symbol first (truncated cone: first-angle shows the circle on the left of the trapezium; third-angle shows it on the right). Then apply the rule for that system: first-angle places the plan below the front view and the side view on the right; third-angle reverses both. Redraw 10 given multiview problems, labelling each view and the projection system.
Producing dimensioned drawings that are technically incomplete - missing overall dimensions, duplicating a dimension, dimensioning to a hidden line, or omitting radius/diameter symbols and the number of holes.
Candidates focus on getting the shape right and treat dimensioning as an afterthought. They also do not know the drafting standards for symbols (Ø, R, □, M, the '2×' multiplier) or the rule that each feature is dimensioned once only, on the view where it appears clearest.
What to do instead
Adopt a checklist applied to every drawing: overall length, width and height; every hole with Ø and quantity; every radius with R; no dimension repeated across views; no dimension on a hidden line; units and title block complete. Practise redrawing a part and then auditing it against the checklist before moving on.
Choosing a material by name alone (e.g. 'use mild steel because it is strong') without linking the service requirement - strength, hardness, corrosion resistance, machinability, cost - to a specific material property or test.
Candidates memorise material names and a few properties but never practise the selection reasoning. Exam questions often give a service condition (wear resistance, marine environment, high-temperature creep) and expect the candidate to justify a choice from properties, not from habit.
What to do instead
Build a comparison table of the main engineering materials (mild steel, medium-carbon and high-carbon steel, cast iron, stainless steel, aluminium alloys, brass, bronze, polymers) with tensile strength range, hardness, corrosion behaviour, machinability and typical applications. For each, write a two-sentence justification of when you would select it and when you would not.
Confusing material testing and heat-treatment terminology - mixing hardness tests (Brinell, Rockwell, Vickers) with impact or tensile tests, or describing annealing, normalising, hardening and tempering as if they were the same process.
The names are learned in lists rather than as distinct procedures with distinct purposes and outcomes. Candidates remember that 'heating and cooling' is involved in all of them and blur the cooling rates, the resulting microstructure and the property change.
What to do instead
Write a table with columns: process, heating temperature range, cooling method and rate, resulting structure, effect on hardness and ductility, typical purpose. Do the same for tests: what is measured, the indenter or specimen used, typical scale, and one application. Recite both tables until you can reproduce them without notes.
Selecting the wrong hand tool or measuring instrument for a task and misreading its resolution - using a vernier caliper to 0.02 mm without reading the vernier scale correctly, or using a try square where a micrometer is needed.
Candidates are familiar with the instruments in principle but have not practised reading scales. Vernier and micrometer readings require a specific procedure (main scale plus vernier coincidence; thimble and barrel), and under exam conditions candidates round or misread the graduations.
What to do instead
Practise 30 readings each on vernier caliper, micrometer screw gauge and vernier height/depth gauge, writing down the main-scale value, the vernier or thimble value, and the total. Also list the resolution and typical use of each instrument (steel rule 0.5 mm, caliper 0.02 mm, micrometer 0.01 mm, dial test indicator 0.01 mm) and match them to tasks.
Ignoring tool maintenance and safe-use conditions - describing a chipped file, a mushroomed chisel head, a blunt drill or an unguarded grinding wheel as acceptable, or omitting the need to check a tool before use.
Candidates answer tool questions as if tools are always in good condition and skip the pre-use inspection step. They also do not connect tool condition to outcome, so they miss questions that ask why a blunt drill causes work-hardening or why a mushroomed chisel is dangerous.
What to do instead
For every tool category, learn the inspection points (file: handle secure, teeth clean, no pinning; chisel: head not mushroomed, edge correct angle; drill: sharp, correct point angle; grinding wheel: ring test, guard in place, maximum speed marked) and the consequence of each defect. Frame answers as 'check, then use, then maintain'.
Treating Nigerian regulatory and professional bodies as interchangeable - attributing registration of engineers to the wrong body, or confusing COREN's statutory mandate with that of NSE, SON, or the Council of Registered Builders.
Candidates learn the acronyms without learning the functions. COREN (Council for the Regulation of Engineering in Nigeria) is the statutory regulator under the Engineers (Registration, etc.) Act; NSE is the voluntary professional society. Candidates who do not separate statutory regulation from professional membership give confident but wrong answers.
What to do instead
Write a one-page map: body, legal basis, core function, who it registers or certifies. Include COREN (registration and licensing of engineers, engineering technologists and technicians; discipline; accreditation of engineering programmes), NSE (professional society, advocacy, CPD), SON (standards), and the relevant safety and factory legislation. Test yourself by matching each function to a single body.
Answering ethics and safety scenarios with the 'obvious' safe answer rather than applying the specific duty - for example, saying a registered engineer should 'report to the client' when the correct path is to refuse to certify non-compliant work, record the decision, and escalate to the regulator or relevant authority.
Scenario questions reward procedural reasoning, but candidates respond with generalities about being honest and careful. They also overlook the hierarchy of duties (public safety first, then employer/client, then self) and the requirement to keep records and decline to sign off work they cannot verify.
What to do instead
For each scenario, state the duty owed, to whom, the specific action, and the record to be kept. Practise with cases: pressure to approve substandard materials, an unregistered person signing drawings, a site hazard with imminent risk, a conflict of interest in procurement. Learn the principle that public safety and statutory compliance override commercial pressure, and that refusal plus written record is the professional response.