Why Hoist Mast Sections Are 1508 mm

Construction hoists on a high-rise building site

Mast sections on rack-and-pinion construction hoists are 1508 mm high. It is an odd number for a steel structure - until you divide it by the rack pitch.

The arithmetic

Rack pitch is p = pi x m. For module 8, p = 25.1327 mm. Sixty pitches: 60 x 25.1327 = 1507.96 mm. Rounded, that is the 1508 mm section height used across the industry.

Why the section follows the rack

Each mast section carries one rack. When sections are stacked, the last tooth of one rack and the first tooth of the next must be exactly one pitch apart. If the section height were not a whole number of pitches, every joint would need its own correction - and the pinion would hit a short or long pitch every 1.5 m.

With 60 pitches per section, the joint pitch is set by placing each rack at the same position on its section. That turns a mast of 60 sections into a single continuous rack - provided every rack is machined to the same datum.

Rack on the mast section and a 15-tooth module 8 pinion

What it means when buying racks

· The distance from section end to first tooth matters as much as the tooth form. Give it on the drawing.

· Hole positions and tooth positions should come from one machining datum.

· Racks from different suppliers or batches can mix on one mast only if both follow the same joint geometry.

· A joint pitch error shows up as a knock at every section and accelerates wear at the joints.

Related numbers

· A 15-tooth module 8 pinion travels 15 x 25.13 = 377 mm per revolution - four revolutions per section, almost exactly (1508 / 377 = 4.0).

· Tooth depth for module 8 on the ISO 53 basic profile is 2.25 x 8 = 18 mm.

Summary

1508 mm is not a structural choice but a gear choice: 60 teeth of module 8. Racks for hoist masts should be specified with their joint geometry, not only their module.

For drawings, samples or a quotation, send us your rack, pinion or gear specification and quantity.