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Rolling parallel ruler (blade on two notched rollers)

How does a rolling parallel ruler stay parallel? · Hardware · basis: Xem Studio design following Brown No. 323 (1868)

Also called: rolling parallel ruler, rolling ruler, roller parallel rule, regla paralela de rodillos, Rollparallellineal

Exact dimensions. True size, with no printing tolerance added.

sizes
4 in table

Notes

  • A straight-edge carries an axle with a roller at each end; the rollers are the same size and fixed to the axle, so as the ruler rolls every point of the blade moves the same distance at right angles to the axle — the blade stays parallel to its starting line.
  • The notched rims (24 V-notches, 0.85 mm deep) bite the paper so neither roller slips; the rollers stand 1 mm proud of the underside through openings in the blade. Drawn with a Ø3 × 150 axle, Ø18 × 4 rollers at ±60 mm and a 200 mm blade.
  • Brown's No. 323 (rolling parallel ruler); the navigator's parallel rule.
  • Parts (each has its own page): rolling-ruler-blade-200-d18, notched-roller-d18x4-b3, linear-shafts-h6.
  • Brown's movement No. 323 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Rolling parallel ruler size chart

parametervalue
blade200 × 24 × 6 mm
rollers2 × Ø18 × 4, notched
axleØ3 × 150 (linear shaft)
roller spacing120 mm

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Henry T. Brown (1868, public domain)Five Hundred and Seven Mechanical Movements — scan on archive.orgwebPublisher's page; dimensions are facts
507movements.comBrown's movement No. 323: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

rolling-parallel-ruler-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
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Plain text: sheet.txt · JSON: /api/geometry?object=rolling-parallel-ruler-mechanism

Rolling parallel ruler (blade on two notched rollers), isometric render of a generated part
Render of rolling-parallel-ruler-mechanism-assembly from the free STEP; not to scale.

Fits with

Rolling parallel ruler blade 200 × 24 × 6 with lugs for a Ø3 axle, isometric render of a generated part
Rolling parallel ruler blade 200 × 24 × 6 with lugs for a Ø3 axle200.0×24.0×13.0 mm★ 1 file
Notched roller Ø18 × 4, Ø3 bore, 24 V-notches, isometric render of a generated part
Notched roller Ø18 × 4, Ø3 bore, 24 V-notches17.93×17.93×4.0 mm★ 1 file
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long, isometric render of a generated part
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long10 sizes★ 70 files

Questions

How does a rolling parallel ruler stay parallel?

A straight-edge carries an axle with a roller at each end; the rollers are the same size and fixed to the axle, so as the ruler rolls every point of the blade moves the same distance at right angles to the axle — the blade stays parallel to its starting line.

Why does a rolling ruler need equal rollers?

Unequal rollers would make the blade swing about the smaller one; equal, fixed rollers make every point travel the same distance.