A Section Liner is a hand-held draughting device that rules a series of equally spaced parallel lines onto a drawing — the hatching that fills the cut faces of a sectioned part on an engineering drawing. Mechanical and architectural drafting offices relied on it before CAD took over. The tool indexes itself by a fixed step (commonly 1 mm to 3 mm) so each new line sits at the correct offset from the previous one. The result is uniform section hatching drawn in a fraction of the time a T-square and scale would take.
Section Liner Interactive Calculator
Vary rack pitch, hatch count, indexing error, and hatch angle to see total drift, rack travel, and the resulting hatched field.
Equation Used
This calculator follows the section liner indexing example: each rack tooth gives one fixed pitch advance, while pitch error accumulates across the hatch count. The projected hatch span uses the line angle term from the article formula.
- Each pawl click advances exactly one rack pitch.
- Pitch error is treated as worst-case cumulative error in the same direction.
- Line count follows the article example convention of 50 indexed lines.
- Hatch span is the projected width normal to the drawing edge.
The Section Liner in Action
The mechanism is simple, but the tolerances are not. A Section Liner has a straightedge that carries a ratcheted or cammed indexing mechanism. You rule one line, lift the edge slightly, advance one click, and rule the next. The click corresponds to a fixed linear step — say 2.0 mm — and that step has to repeat to within roughly ±0.05 mm across 50 lines or you will see the hatching drift visibly across a sectioned area. Drift of 0.1 mm per line accumulates to 5 mm by line 50, and the eye picks that up immediately as a fan rather than a parallel field.
The indexing pawl rides on a fine rack or a screw-driven cam. On the better instruments — Kern, Riefler, and the Haff parallel ruling devices from the early 20th century — the rack is hardened steel cut to DIN tolerances, and the pawl drops into each tooth under spring pressure. Cheap copies use a stamped sheet-metal rack and the spacing wanders within 10 lines. If you notice your section lines bunching at one end of the hatched area, the pawl spring has weakened or the rack teeth are burred. If the lines cross each other, the straightedge is not parking parallel between strokes — usually a worn guide rail or a loose pivot in the indexing head.
Line angle matters too. Section hatching by drawing convention sits at 45° to the principal axes of the part, and the Section Liner either clamps to a drafting machine's protractor head or carries its own 45° reference fence. Off-angle by more than 1° and the drawing reads as sloppy even if the spacing is perfect.
Key Components
- Straightedge blade: The ruling edge itself, typically 200 mm to 400 mm of ground steel or anodised aluminium with a bevelled inking lip. Edge straightness must hold to within 0.02 mm over the full length or ink lines will visibly bow.
- Indexing rack: A fine-toothed rack — usually 0.5 mm, 1 mm, or 2 mm pitch — that defines the line-to-line step. Pitch error compounds, so the rack is cut to ±0.01 mm per tooth on quality instruments.
- Pawl and spring: Drops into each rack tooth under 2-4 N spring force to lock the next position. A tired spring lets the pawl skip teeth, which is the most common failure you'll see — random wide gaps in the hatching.
- Lift cam or thumb lever: Disengages the pawl so you can lift the straightedge to rule the next line, then re-engages it cleanly on the next tooth. The cam dwell has to be long enough that you don't catch the rack mid-stroke.
- Angle reference fence: Locks the ruling angle to 45° (or whatever the drawing standard demands — 30° and 60° are also common for material-specific hatching). Fence repeatability must be within ±0.25° to keep hatching visually parallel.
Who Uses the Section Liner
Section Liners earned their place in any drafting office that produced sectioned views in volume. Before CAD, a single complex assembly drawing might carry 20 sectioned features, each needing 30 to 100 hatch lines. Doing that by hand with a scale and T-square took an hour per view; the Section Liner cut it to minutes. Different trades adopted different spacings and angles depending on the standard — DIN, ANSI, BS, JIS — and the tool had to handle all of them.
- Mechanical engineering drafting: Filling section views in machine-component drawings to ISO 128-50 — Kern of Aarau supplied Section Liners as standard kit with their drafting machines into the 1980s.
- Architectural drafting: Hatching wall sections, floor cuts, and material call-outs on building plans drafted on Mutoh or Kuhlmann drafting boards.
- Patent illustration: Producing the parallel shading required by USPTO drawing rules on hand-inked patent figures, where consistency across many figures matters for examiner clarity.
- Cartography and map shading: Drawing relief hachures and uniform tone fields on hand-drawn topographic sheets at agencies like the Ordnance Survey before raster shading replaced manual work.
- Technical illustration: Filling cutaway views in service manuals — Haynes and Chilton automotive manuals through the 1970s used hand-ruled hatching produced with parallel ruling devices.
- Heritage drawing restoration: Re-inking faded section views on archived shipyard drawings at maritime museums where the original drafting style must be preserved.
The Formula Behind the Section Liner
The practical question with a Section Liner is how many lines you need to fill a given hatched area at a given spacing — and how long the rack on your instrument must be to do it without re-indexing. At fine spacing (0.5 mm) the hatching reads dense and dark, suitable for small-scale views but slow to draw. At coarse spacing (3 mm) the hatching reads light and open, good for large architectural sections but visually weak on small machine details. The sweet spot for general mechanical drafting sits around 2 mm — dense enough to read as solid hatching at A3 print scale, open enough that 50 lines doesn't take half an hour.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Nlines | Number of section lines required to fill the hatched area | count | count |
| Larea | Width of the hatched area measured perpendicular to the drawing axes | mm | in |
| s | Indexed spacing between adjacent section lines (the rack pitch) | mm | in |
| θ | Hatching angle measured from the perpendicular to the area width | degrees | degrees |
Worked Example: Section Liner in a heritage aircraft drawing reproduction project
A retired aerospace draughtsman in Toulouse is reproducing a 1958 Sud Aviation Caravelle wing-rib sectional drawing for a museum display. The original was drawn at 1:5 scale on linen, and the sectioned rib cap area measures 120 mm wide on the new sheet. He's using a Standardgraph Section Liner with a 2 mm rack pitch, drawing at the conventional 45° angle, and needs to know how many lines the hatching will take and how long the rack engagement needs to be.
Given
- Larea = 120 mm
- s = 2.0 mm
- θ = 45 degrees
Solution
Step 1 — at the nominal 2 mm rack pitch, calculate the perpendicular spacing component:
Step 2 — divide the hatched width by that perpendicular spacing to get the line count:
Step 3 — at the fine end of the typical operating range, 1 mm pitch:
That's nearly twice the work — and at 170 lines you're pushing the rack length on most pocket Section Liners, which top out around 200 teeth. The hatching reads almost solid black at print scale, which is fine for a small detail callout but overkill for a 120 mm rib section. At the coarse end, 3 mm pitch:
57 lines reads light and airy — appropriate for an architectural wall section but visually weak on a mechanical part where the hatching needs to clearly distinguish the cut face from adjacent unsectioned geometry. The 2 mm nominal hits the sweet spot: 85 lines, around 4-5 minutes of work, and the result reads as proper mechanical hatching at A3 print.
Result
The nominal result is 85 section lines at 2 mm pitch to fill the 120 mm rib cap area. That's about 4-5 minutes of work for a practiced hand, and the hatching will read as a clean medium-density fill at the museum's A3 reproduction scale. The 1 mm fine setting doubles the line count to 170 and the time, producing dense hatching that overpowers small features; the 3 mm coarse setting drops to 57 lines but reads visually weak on machine drawings. If you measure the actual line count and find it 5-10% off — say 78 lines instead of 85 — the rack pitch is the first thing to check: a worn Standardgraph rack often runs long by 0.05-0.1 mm per tooth after 30 years of use. If the lines are present but visibly non-parallel, the angle fence has slipped, and on a Kern-style instrument that's almost always the locking thumbscrew bedding into a worn detent. If you see clusters of two or three lines bunched together, the pawl spring has fatigued and is letting the pawl drop into the same tooth twice before advancing.
Choosing the Section Liner: Pros and Cons
Section Liners compete with several other ways to produce parallel hatching — and CAD has effectively replaced all of them in production drafting. The comparison still matters for restoration work, patent figures, and any setting where hand-drawn hatching is the deliverable.
| Property | Section Liner | T-square + scale (manual) | CAD hatch fill |
|---|---|---|---|
| Spacing accuracy across 50 lines | ±0.05 mm cumulative | ±0.5 mm cumulative | Exact (digital) |
| Lines per minute (practiced hand) | 20-25 | 5-8 | N/A — instant fill |
| Tool cost (period equivalent) | $80-300 (Kern, Standardgraph) | $15-30 | $0 incremental, $1000+ CAD seat |
| Setup time per hatched area | 10-15 sec (set angle, pitch) | 30-60 sec (mark each line) | 2-3 sec (pick boundary) |
| Suitable for ink vs pencil | Both — bevelled lip handles ink | Both, but ink smears easily | Plotter or print |
| Failure mode on volume work | Pawl spring fatigue after ~10,000 cycles | Operator drift, fatigue | None mechanical |
| Best application fit today | Restoration, patent figures | Quick one-offs | All production drafting |
Frequently Asked Questions About Section Liner
This is the angle fence drifting between strokes, not a rack problem. As you lift and re-set the straightedge for each line, any slop in the angle reference — a worn pivot, a loose thumbscrew, a bent locating pin — lets the blade rotate by a fraction of a degree. Half a degree of drift over 50 lines puts the last line 5-6 mm out of parallel with the first.
Check the angle fence by drawing two lines at opposite ends of a long sheet without changing the setting, then measure the perpendicular distance at both ends. If it varies by more than 0.3 mm over 300 mm, the fence needs re-bedding. On Kern instruments the fix is usually replacing the brass detent ball; on Standardgraph it's tightening the central pivot screw.
Match the visual line density to the final print size, not the original sheet size. The eye reads hatching as solid grey when lines sit closer than about 0.5 mm apart on the printed page. Work backward from there: if you're drawing at 1:1 and printing at 1:1, 2 mm pitch reads as clean discrete lines. If you're drawing at 2:1 and printing reduces it back to 1:1, your 2 mm pitch becomes 1 mm on print and starts to grey out.
Rule of thumb: pick the pitch so that printed line spacing lands between 1.0 mm and 2.5 mm. Below 1 mm reads muddy; above 2.5 mm reads sparse and unprofessional on machine drawings.
If a fresh spring didn't solve it, the pawl tip is rounded or the rack teeth are burred — both common after decades of use. Pull the pawl and inspect the engagement face under 10× magnification. A sharp pawl tip should show a crisp 90° corner; if it's rounded to a visible radius, the pawl is climbing out of the tooth under lift load instead of indexing cleanly.
Burred rack teeth show as bright spots on the leading flank. A few minutes with a fine Arkansas stone dressing the pawl tip back to square usually restores reliable indexing. If the rack itself is burred, you're better off finding a donor instrument — re-cutting a hardened rack is not a field repair.
Yes, if the angle fence supports those settings — most professional instruments from Kern, Standardgraph, and Haff have detents at 30°, 45°, and 60°. ISO 128-50 calls for 45° as the default for solid materials, but parallel hatching at adjacent components must use different angles (typically 30° and 60°) to visually separate the parts in an assembly section.
What you need to verify is angle repeatability between strokes, not just angle accuracy. A fence that hits 30° dead-on but wanders ±0.5° between settings will produce visibly non-parallel hatching even though the average angle is correct.
It's almost always the ink and the paper, not the tool. Original 1950s-70s drafting work used India ink on linen or vellum, both of which absorb ink with a controlled bleed that produces sharp consistent line edges. Modern bond paper and most ballpoint or rollerball inks bleed inconsistently along the fibre direction, so each line picks up a slightly different edge profile.
If you're doing restoration work, source proper drafting vellum (Clearprint 1000H or similar) and use a Rotring rapidograph with archival India ink. Line crispness will jump immediately. The Section Liner itself isn't the limiting factor on visual quality once the rack and pawl are sound.
Restore the old one. Modern production of dedicated Section Liners essentially stopped in the 1990s when CAD took over drafting, and what's available new today is mostly low-tolerance student-grade equipment with stamped racks. A clean 1960s Kern, Riefler, or Haff instrument with intact rack and a fresh pawl spring will outperform anything currently manufactured.
Budget-wise, a serviceable used Standardgraph runs $40-80 on the European secondhand market, and a Kern in good condition $150-250. Restoration cost is typically just a spring and an hour of cleaning. The only case for buying new is if you genuinely cannot source a used instrument — and even then, a vintage parallel ruler with a separate indexing scale outperforms most new Section Liners.
References & Further Reading
- Wikipedia contributors. Technical drawing tool. Wikipedia
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