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Crank, slotted arm and toothed sector driving a rack

How does a crank in a slotted arm move a rack back and forth? · Hardware · basis: Xem Studio design following Brown No. 131 (1868)

Also called: sector and rack, crank slotted arm rack, oscillating sector rack, manivela, brazo ranurado y sector dentado, Kurbelschleife mit Zahnsegment und Zahnstange

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

sizes
5 in table

Notes

  • A crank pin, in a slide block, runs in the slot of an arm pivoted 70 mm from the crank centre: the arm rocks through ±9.9° (sin⁻¹ 12/70). A 60-tooth sector on the same pivot turns with the arm and drives a rack below: the rack moves R × angle = 30 mm × 0.346 rad = 10.4 mm total, each way, with the quick-return timing of the slotted lever.
  • Drawn at crank angle 200°: arm at 9.71°, rack 5.08 mm from mid-stroke, teeth meshed on the sector's pitch circle.
  • Brown's No. 131 (rectilinear motion of a rack from a crank by a slotted arm and toothed sector).
  • Parts (each has its own page): slotted-arm-sector-gear-m1-60t-60deg-b5, gear-rack-m1-120-full-depth, crank-disc-36-pin-r12, slide-block-12x6, dowel-pins-metric.
  • Brown's movement No. 131 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Crank, slotted arm and toothed sector driving a rack size chart

parametervalue
crank radius12 mm
pivot distance70 mm
arm swing±9.9°
sector60 T, R30
rack stroke10.4 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. 131: 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

crank-slotted-arm-sector-rack-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=crank-slotted-arm-sector-rack-mechanism

Crank, slotted arm and toothed sector driving a rack, isometric render of a generated part
Render of crank-slotted-arm-sector-rack-mechanism-assembly from the free STEP; not to scale.

Fits with

Slotted arm with a 60° toothed sector (module 1, 60 T), Ø5 bore, isometric render of a generated part
Slotted arm with a 60° toothed sector (module 1, 60 T), Ø5 bore28.85×138.98×8.0 mm★ 1 file
Gear rack, module 1, 120 mm, full-depth 20° teeth, isometric render of a generated part
Gear rack, module 1, 120 mm, full-depth 20° teeth120.0×11.0×8.0 mm★ 1 file
Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm, isometric render of a generated part
Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm36.0×36.0×5.0 mm★ 1 file
Slide block 12 × 6.2 mm for a 6.4 mm slot, isometric render of a generated part
Slide block 12 × 6.2 mm for a 6.4 mm slot2 sizes★ 1 file
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325), isometric render of a generated part
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)5 sizes★ 23 files

Questions

How does a crank in a slotted arm move a rack back and forth?

A crank pin, in a slide block, runs in the slot of an arm pivoted 70 mm from the crank centre: the arm rocks through ±9.9° (sin⁻¹ 12/70). A 60-tooth sector on the same pivot turns with the arm and drives a rack below: the rack moves R × angle = 30 mm × 0.346 rad = 10.4 mm total, each way, with the quick-return timing of the slotted lever.