Synchronous belts GT2 HTD XL
Toothed synchronous belts transmit motion without slipping with a mechanical efficiency that can reach 98%, thanks to the positive engagement between the belt teeth and the pulleys. The GT2, HTD and XL profiles represent three families widely used in automation, 3D printing and light machine tools. Their design eliminates the need for lubrication, reduces maintenance and allows fixed transmission ratios. The GT2 profile, with a 2 mm pitch, is the current standard in precision positioning systems, while HTD (High Torque Drive) is used where higher load capacity is required and the XL profile (5,08 mm pitch) remains in legacy equipment and general transmission applications.
Tooth profiles and nomenclature
Section titled “Tooth profiles and nomenclature”Tooth geometry defines the dynamic behavior and load capacity of each profile. GT2 uses curvilinear teeth with 2 mm pitch, optimized to minimize backlash and reduce noise. The HTD family, developed by Gates, uses circular arc teeth and is available in standardized metric pitches: 3M (3 mm), 5M (5 mm), 8M (8 mm) and 14M (14 mm). The XL (extra light) profile is a trapezoidal profile with 1/5″ (5,08 mm) pitch, defined under ISO 5296, and was one of the first industrial synchronous pitches.
| Profile | Metric pitch (mm) | Imperial pitch (in) | Tooth shape |
|---|---|---|---|
| GT2 | 2 | 0,0787 | Curved (modified PowerGrip) |
| HTD 3M | 3 | 0,118 | Curved (circular arc) |
| HTD 5M | 5 | 0,197 | Curved (circular arc) |
| HTD 8M | 8 | 0,315 | Curved (circular arc) |
| HTD 14M | 14 | 0,551 | Curved (circular arc) |
| XL | 5,08 | 0,200 | Trapezoidal |
Standard dimensions
Section titled “Standard dimensions”The available widths and lengths for GT2 neoprene belts with fiberglass core are summarized below, according to commercial data from compatible PowerGrip GT belts. For other profiles, typical widths by pitch are indicated.
GT2 belts (2 mm pitch)
First sentences with numerical data: the GT2 profile is supplied in widths of 6 mm / 0.236 in and 9 mm / 0.354 in, with pitch lengths from 99 mm / 3.90 in up to more than 1 164 mm / 45.83 in.
| Width (mm / in) | Representative pitch length (mm / in) | Number of teeth | Reinforcement | Tooth finish | Working temperature |
|---|---|---|---|---|---|
| 6 / 0,236 | 100 / 3,937 | 50 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 140 / 5,512 | 70 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 200 / 7,874 | 100 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 280 / 11,024 | 140 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 400 / 15,748 | 200 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 600 / 23,622 | 300 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 6 / 0,236 | 1 164 / 45,827 | 582 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 9 / 0,354 | 99 / 3,898 | 33 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 9 / 0,354 | 189 / 7,441 | 63 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
| 9 / 0,354 | 240 / 9,449 | 80 | Fiberglass | Nylon coating | -34 °C to 82 °C / -30 °F to 180 °F |
Typical widths for other profiles
| Profile | Available widths (mm / in) |
|---|---|
| HTD 3M | 6 / 0,236 – 15 / 0,591 |
| HTD 5M | 9 / 0,354 – 25 / 0,984 |
| HTD 8M | 20 / 0,787 – 50 / 1,969 |
| XL | 6,4 / 0,250 – 12,7 / 0,500 |
Materials and construction
Section titled “Materials and construction”The body of synchronous belts is mainly manufactured from neoprene with excellent resistance to weather and ozone, although it can degrade with continuous contact with oil and fuel. The tensile cords are fiberglass (sometimes steel or Kevlar in high-load applications), ensuring low elongation and high fatigue resistance. The teeth incorporate a nylon coating that reduces friction between belt and pulley, minimizes wear and contributes to quiet operation. The continuous working temperature is between ‑34 °C / ‑30 °F and 82 °C / 180 °F, with permissible peaks up to 100 °C / 212 °F for short periods.
| Component | Typical material | Main function |
|---|---|---|
| Body | Neoprene | Cushioning, transmission of tooth thrust |
| Tensile member | Fiberglass | Resistance to elongation and breaking load |
| Tooth coating | Nylon | Low friction, wear protection |
Load capacity
Section titled “Load capacity”The power transmitted by a synchronous belt is determined from the difference in tension between the tight side and the slack side. The general expression is P = (F₂ - F₁) · r · ω, where P is power in watts, F₂ and F₁ are forces in Newtons, r is the pulley radius in meters and ω is angular velocity in rad/s. For a 6 mm wide GT2 belt working at 1 000 rpm on a 20-tooth pulley, the power capacity can reach approximately 0,12 kW / 0,16 HP under continuous service conditions.
Approximate capacity for GT2 belt (width 6 mm, 20-tooth pulley, fiberglass)
| Pulley speed (rpm) | Allowable power (kW / HP) |
|---|---|
| 500 | 0,06 / 0,08 |
| 1 000 | 0,12 / 0,16 |
| 1 500 | 0,18 / 0,24 |
| 2 000 | 0,24 / 0,32 |
Exact values for each pitch-width-speed combination should be obtained from the manufacturer’s tables. HTD belts, thanks to their higher load capacity, can handle powers up to 5 kW / 6,7 HP in 8M formats at high speeds.
Selection criteria
Section titled “Selection criteria”The choice of synchronous profile depends on the required accuracy, dynamic load and operating speed. For low-torque and precise positioning applications — such as 3D printers or pick-and-place arms — the GT2 6 mm profile prevails due to its reduced backlash. When load demand increases, migrate to HTD 5M or 8M, capable of transmitting more than 1 kW / 1,34 HP without slipping. The XL profile is reserved for old machines, slow conveyors and linear actuators where synchronization is necessary but loads are low, typically below 0,1 kW / 0,13 HP.
| Application | Recommended profile and width | Typical power range (kW / HP) |
|---|---|---|
| 3D printer (X/Y axis) | GT2 6 mm | 0,01 – 0,04 / 0,013 – 0,054 |
| Desktop CNC | GT2 9 mm or HTD 3M 9 mm | 0,03 – 0,15 / 0,04 – 0,20 |
| Light cartesian robot | HTD 5M 15 mm | 0,10 – 0,50 / 0,13 – 0,67 |
| Light load conveyor | HTD 5M 25 mm | 0,20 – 1,00 / 0,27 – 1,34 |
| Machine tool (feed axis) | HTD 8M 30 mm | 0,50 – 2,50 / 0,67 – 3,35 |
| Legacy synchronous transmission | XL 1/4″ | < 0,10 / < 0,13 |
Mounting and tensioning
Section titled “Mounting and tensioning”Proper installation begins with pulley alignment, which must be maintained within ±0,2° angular deviation per 100 mm / 3,94 in of center distance. Initial tension is adjusted to obtain a belt elongation between 1% and 2% of its free length. This can be verified by applying a force perpendicular to the belt at the span center and measuring the deflection; for example, for a 6 mm GT2 with a free length of 120 mm / 4,72 in, a deflection of 1,2 mm – 2,4 mm / 0,047 in – 0,094 in is recommended under a tightening load of 1 N / 0,225 lbf. Overtightening accelerates tooth wear and increases bearing load, while insufficient tension causes tooth jumping (ratcheting), especially during sudden starts and stops.
Typical applications
Section titled “Typical applications”- Automation and robotics: linear motion axes in pick-and-place equipment, low-cost CNC systems and X‑Y tables, where the 2 mm pitch allows positioning resolutions below 0,1 mm / 0,004 in.
- 3D printing: 6 mm GT2 belts move the print carriages in FDM machines, supporting traverse speeds up to 300 mm/s / 11,8 in/s.
- Food and pharmaceutical industry: HTD belts in stainless steel for synchronized conveyors, operating in temperature ranges from ‑10 °C to 80 °C / 14 °F to 176 °F.
- Machine tools: HTD 8M and 14M profiles are used in secondary drives of milling machines and lathes with powers from 1 kW to 5 kW / 1,34 HP to 6,7 HP.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the exact pitch of a GT2 belt?
Section titled “What is the exact pitch of a GT2 belt?”The pitch is 2 mm / 0,0787 in, and it is the same for all lengths and widths of the series.
What maximum temperature can a GT2 neoprene belt withstand?
Section titled “What maximum temperature can a GT2 neoprene belt withstand?”The continuous working temperature reaches 82 °C / 180 °F; above 100 °C / 212 °F the material degrades rapidly.
How much torque can a 6 mm GT2 transmit at 1 000 rpm?
Section titled “How much torque can a 6 mm GT2 transmit at 1 000 rpm?”With a 20-tooth pulley it can transmit approximately 1,15 N·m / 0,85 lbf·ft, equivalent to about 0,12 kW / 0,16 HP.
What is the expected service life of an HTD belt under normal conditions?
Section titled “What is the expected service life of an HTD belt under normal conditions?”Manufacturers estimate between 15 000 and 20 000 hours of continuous operation if tensioning and alignment conditions are respected.
How often should the tension of a synchronous belt be inspected?
Section titled “How often should the tension of a synchronous belt be inspected?”It is recommended to check the tension every 500 service hours or at each scheduled maintenance stop.
Does the number of pulley teeth affect the transmissible power?
Section titled “Does the number of pulley teeth affect the transmissible power?”Yes; when decreasing from 20 to 14 teeth on a GT2 pulley, the allowable power is reduced by about 15 % due to the smaller wrap angle.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/belt-transmission-power-efficciency-d_1378.html
- mcmaster.com: https://www.mcmaster.com/products/gt-timing-belts