Toothed belts for drives: module selection
AT, HTD, GT profiles for toothed belts: how to choose the pitch, width and module for a conveyor drive load.
A toothed belt transmits torque without slipping — unlike a V-belt, it synchronises the driving and driven shafts precisely. This makes it indispensable where position matters: feeding mechanisms, dispensers, synchronised conveyor sections. In this article we break down how to choose the profile, pitch and width of a toothed belt for a real load.
Why toothed, not V-belt
A V-belt works through friction and always has a small slip — 1–2% under load. For a belt drive this is acceptable, but for a mechanism requiring precise synchronisation it is not acceptable at all. A toothed belt engages with its teeth on the pulley and transmits motion without position loss.
Typical tasks where we use a toothed belt specifically:
- Driving dispensers and feeding mechanisms where the exact dose matters.
- Synchronising two conveyors that must run “in step”.
- Driving rotary tables and indexing mechanisms.
- Replacing a chain drive where quiet, clean operation without lubrication is needed.
Toothed belt profiles
The tooth profile determines what torque the belt can transmit. The most common systems:
| Profile | Pitch | Tooth shape | Typical application |
|---|---|---|---|
| MXL / XL | 2.03 / 5.08 mm | trapezoid | small mechanisms, low torque |
| L / H | 9.53 / 12.7 mm | trapezoid | general-purpose drives |
| HTD 5M / 8M | 5 / 8 mm | semicircular | conveyors, medium torque |
| GT2 / GT3 | 3 / 5 mm | modified | precise positioning, high torque |
| AT5 / AT10 | 5 / 10 mm | AT trapezoid | power drives, minimal backlash |
The trapezoidal profile (MXL, XL, L, H) is the cheapest but concentrates stress at the tooth root. The semicircular HTD distributes the load more evenly and transmits more torque at the same width. GT is a development of HTD with minimal backlash; we choose it for precise positioning. AT is a flat-root profile for power drives with strict synchronisation requirements.
How to choose the module for the load
We select a toothed belt by four parameters: transmitted torque, rotation speed, centre distance and width. The calculation sequence:
- Determine the required torque with a margin — multiply the working torque by a service factor of 1.3–1.8.
- From torque and speed, choose the profile (pitch) by the manufacturer’s nomogram.
- Select the belt width so the specific load is within tolerance.
- Check the number of teeth in mesh with the pulley — at least 6 for reliable transmission.
Engineer’s tip. Do not chase a narrow belt for compactness. If fewer than 6 teeth are in mesh, the teeth shear off under start-up load. It is better to take a wider belt of smaller pitch — it is quieter and lasts longer.
Tensioning and maintenance
A toothed belt does not need tensioning as often as a V-belt, but undertensioning is dangerous: under load the teeth “jump” over the pulley grooves, which destroys the belt in minutes. Overtensioning loads the shaft bearings and shortens their life.
Correct tension is checked by deflection or with a frequency meter — by the resonant frequency of the free span. For synchronous belts we set the tension within the narrow range the manufacturer specifies and check it at every service. We work out the drive and transmission selection together with the line’s conveyors and transporters, and we match the belt material to the food-zone requirements. More on drive elements — in articles tagged drive.
Separate attention goes to shaft alignment and parallelism. A toothed belt is sensitive to skew: with misaligned pulleys it shifts towards one flange, the edge wears, and the teeth are loaded unevenly. So during mounting we check shaft parallelism with a level and a straightedge, and on critical drives we fit pulleys with flanges on both sides. The belt material also matters: a polyurethane base with a steel or aramid cord hardly stretches, while a rubber one gradually elongates and needs re-tensioning.
Signs of wear and when to replace
A toothed belt is a consumable, but its life is easy to extend if wear is noticed in time. The characteristic signs by which we assess the belt’s condition at service:
- Cracks at the tooth root — the most dangerous defect, the belt can break without warning.
- Wear of the tooth tips — the mesh weakens, the risk of “jumping” appears.
- Edge wear — a sign of pulley misalignment, the belt shifts sideways.
- Glazed side surfaces of the teeth — normal running-in, but accelerated glazing indicates overtensioning.
Preventive replacement on schedule is cheaper than an emergency line stop. The life of a quality synchronous belt in food production is 18–30 months depending on load, washing regime and temperature in the working zone.
Conclusion
A toothed belt means precise transmission without slipping, and its profile is chosen for the torque, not “by availability”. HTD and GT cover most conveyor tasks, AT — power drives with strict synchronisation. If you need to select a drive for a dispenser or a synchronous section, get in touch — we will calculate the belt profile and width for your load.
