Five free practice questions on pattern layout and fabrication: block B of the Red Seal 308A Sheet Metal Worker exam, about 38 of its 120 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A cold-air plenum is insulated on the outside in the shop with foil-faced board held on weld pins and plain speed washers. What is done at each pin and at each joint in the foil facing?
- Staple the facing closed at each joint.
- Cover each pin and joint with foil tape.
- Clip the pins off flush with the facing.
- Rely on the pin washers to close each hole.
Show the answer
B. Correct. On a cold surface the foil facing is the vapour retarder; any pin hole or joint left open lets moist air reach the cold metal, where it condenses in the insulation. Foil tape over every pin and joint keeps the retarder continuous.
Why not the others
A. Staples hold a facing lap together but punch more holes in it. On a cold plenum the joints still need foil tape to keep the vapour retarder sealed.
C. Pins are often trimmed flush before they are taped, but clipping alone leaves each hole through the facing open to moist air. The holes and joints still need foil tape to keep the vapour retarder continuous.
D. A plain speed washer holds the board on the pin; it is not a vapour seal, and moist air gets around it into the insulation. Each pin and joint is covered with foil tape.
Source: Red Seal Occupational Standard, sub-task B-6.03
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What sets an oblique cone apart from a right cone when its pattern is developed by radial lines?
- Its pattern is one sector swung from the apex.
- Each element is shorter than it shows in elevation.
- Each element has its own true length from the apex.
- Its elements become parallel on the stretch-out.
Show the answer
C. Correct. An oblique cone's apex is not over the centre of its base, so its elements run from the apex at different lengths. Each one's true length is found in a true-length diagram before the pattern is built element by element from the apex.
Why not the others
A. A single sector swung from the apex is the right cone's pattern, where every element is the same length. An oblique cone's elements differ, so its base edge on the pattern is not one arc.
B. No view shows a line longer than it is; an element not parallel to the view shows shorter than its true length. The real difference is that the elements differ from one another, so each needs its own true length.
D. Parallel elements belong to cylinders and prisms, developed by parallel lines. An oblique cone's elements still meet at the apex; they only differ in length.
Source: Red Seal Occupational Standard, sub-task B-5.03
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Black iron for a painted decorative panel is ordered as cold-rolled rather than hot-rolled sheet. Why?
- It is primed at the mill, so it goes straight to the top coat.
- It resists rusting better, so it can go without any finish.
- Its mill scale gives the paint a rougher surface to grip.
- It has a smooth, scale-free surface and closer tolerances.
Show the answer
D. Correct. Rolled cold after pickling, the sheet has a smooth surface with no mill scale and closer thickness and flatness, so it forms evenly and takes a fine paint finish; hot-rolled carries mill scale that must be removed.
Why not the others
A. Cold-rolled black iron comes bare, often with a light oil film against rust in storage, not primed. It is degreased and primed like any bare steel; its advantage is the smooth, scale-free surface.
B. Cold-rolled sheet is plain carbon steel and rusts like hot-rolled once bare; it still needs its paint system. Its advantage is the surface and tolerance.
C. Mill scale is on hot-rolled, not cold-rolled, sheet, and paint over loose scale fails when the scale flakes off. Scale is removed before painting.
Source: Red Seal Occupational Standard, sub-task B-8.02
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A 0.8 mm (0.032 in.) copper blank is being rolled into a curved fascia section on slip rolls. After the passes the curve is even except for a short flat strip along the leading and trailing edges. How is this prevented on the next blank?
- Feed the blank faster so the rolls grip the edge sooner.
- Raise the bending roll more and roll the blank in one pass.
- Pre-bend both edges to the radius on a stake or brake.
- Anneal the edges so they bend as easily as the middle.
Show the answer
C. Correct. A slip roll bends the sheet only where it is supported by two rolls and pushed by the third, so the first and last bit never gets curved. Bending both edges to the radius before rolling gives an even curve from end to end.
Why not the others
A. Feed speed does not change where the rolls bend the sheet. The edge stays flat because it is never between all three rolls at once; it has to be pre-formed to the radius before rolling.
B. Setting the bending roll higher only tightens the radius of the body of the blank; the edges still pass the rolls without being bent, so the flats remain.
D. The flats are not caused by the edges being harder; they come from the geometry of the rolls. Softening the edges changes nothing about where the rolls can bend the sheet.
Source: Red Seal Occupational Standard, sub-task B-7.02
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Panels of a galvanized steel plenum are joined at lapped edges. Both sides of every lap can be reached, and the outside face must be left smooth, with no holes or fastener heads showing. Which fastening is used?
- Blind rivets with low-profile heads.
- Self-drilling screws from the inside.
- Resistance spot welds along the laps.
- Countersunk solid rivets set flush.
Show the answer
C. Correct. A resistance spot weld fuses the lapped sheets at a point by passing current between two electrodes clamped on either side of the lap, so it adds no fastener, needs no hole and leaves only a small mark on the face. It needs access to both sides, which this job has.
Why not the others
A. Even low-profile blind rivets need a drilled hole and leave a head on the face; they are the choice when only one side of the work can be reached.
B. Screws need a hole, and driven from the inside their points come through and stick out of the outside face the job requires to be smooth.
D. Countersunk rivets still need a hole through both sheets, and each one shows on the face as a flush disc; the job rules out holes and fastener heads.
Source: Red Seal Occupational Standard, sub-task B-6.04
02Answer key
| Question | Answer | Sub-task |
|---|---|---|
| Q1 | B | Insulates ductwork, fittings and components |
| Q2 | C | Develops patterns using radial line method |
| Q3 | D | Forms specialty products |
| Q4 | C | Forms flashing, roofing, sheeting and cladding |
| Q5 | C | Assembles ductwork, fittings and components |
03What block B covers
Shop work from the flat sheet: pattern development by straight line, parallel line, radial line and triangulation methods, fitting software and CNC nesting, then cutting, forming, lining and assembling duct and fittings, building dampers, hangers and equipment bases, forming flashing, gutters and cladding, and making specialty products in stainless steel, aluminum, copper and plastics, with welded, riveted and polished finishes.
The Red Seal Occupational Standard names this block “Performs fabrication”. It carries 31.7% of the exam, about 38 of the 120 questions, split across four tasks. The share column is each task's weight within the block, as the standard publishes it.
| Task and its sub-tasks | Share of block |
|---|---|
| Performs pattern development Develops patterns using simple and straight line layout; Develops patterns using parallel line method; Develops patterns using radial line method; Develops patterns using triangulation method; Uses computer technology for pattern development | 33% |
| Fabricates sheet metal components for air and material handling systems Cuts ductwork, fittings and components; Forms ductwork, fittings and components; Insulates ductwork, fittings and components; Assembles ductwork, fittings and components; Fabricates dampers; Fabricates hanger systems, supports and bases | 42% |
| Fabricates flashing, roofing, sheeting and cladding Cuts metal for flashing, roofing, sheeting and cladding; Forms flashing, roofing, sheeting and cladding | 9% |
| Fabricates specialty products Cuts material for specialty products; Forms specialty products; Assembles specialty products; Finishes specialty products | 16% |
04What the questions turn on
Count the half gores
The mitre angle of a gored elbow is the turn divided by twice the number of gores less two, since the end gores are half gores. Dividing 90 degrees by 4 gores gives 22.5 degree cuts and an elbow that turns 135 degrees.
Gross versus net stretch-out
Gross stretch-out is the perimeter plus the lock allowances. Braking lines go on the net stretch-out between them, so lay off the pocket allowance first; marks measured from the sheared edge make the first face short and the last face long.
Bend allowance uses the bend angle
The bend allowance formula, degrees times (0.01743R + 0.0078t), takes the angle the metal is bent through from flat. A flange left at a 135 degree included angle is bent 45 degrees, and that arc length is added to the flats.
True length from plan and height
A triangulation line's true length is the hypotenuse of its plan length and its height. With level ends one height serves every line; with a sloping end each height is read from the elevation. Each new point is where two true-length arcs cross.
05The other blocks
The 308A exam has five blocks. Each has its own page of free questions:
The 308A Sheet Metal Worker practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.