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When your robotics build, CNC router, or DIY automation project demands reliable belt tracking without slippage, a poorly matched pulley becomes the weakest link in the entire drive train. Engineers, makers, and hobbyists who work with round PU belts need a U-groove pulley that holds the belt securely in the groove while staying lightweight enough not to add unnecessary rotational inertia. These U grooved aluminum pulleys are engineered specifically for that task.
Each pulley is machined from aluminum alloy, offering a balance of low weight and structural rigidity. The U-shaped groove profile is sized to accept either 6mm or 8mm width PU round belts. Outer diameters range from 20mm to 80mm (approximately 0.79 in to 3.15 in), and bore diameters span 3mm to 20mm (approximately 0.12 in to 0.79 in), giving you the flexibility to match a wide range of shaft sizes. The set screw bore allows secure shaft fixation without additional hardware in most configurations.
Typical applications include desktop CNC belt-drive axes requiring low-backlash round-belt pulleys, small robotics drive systems using 6mm PU round belt transmission, and DIY conveyor or indexing mechanisms where a lightweight aluminum U-groove idler pulley keeps belt tension consistent across the run.
Machined from aluminum alloy for a combination of low rotational mass and sufficient rigidity for continuous belt-drive operation in light-to-medium duty applications.
The groove geometry is shaped to cradle 6mm or 8mm PU round belts, keeping the belt centered and reducing lateral drift during operation — critical for precision CNC and robotics drives.
Ten outer diameter options (20, 30, 40, 50, 60, 80mm) let you dial in the exact speed ratio or belt wrap angle your drive system requires without custom machining.
Eighteen bore diameter options from 3mm to 20mm accommodate a wide range of motor shafts, lead screws, and idler axles commonly found in maker and automation projects.
A radial set screw bore allows the pulley to be locked onto the shaft securely, preventing axial and rotational slip during belt tension loading without requiring a keyed shaft.
Dimensioned to work as a direct replacement or upgrade in standard round-belt drive configurations used in desktop CNC machines, 3D printer extruder drives, and small conveyor systems.
| Material | Aluminum Alloy |
|---|---|
| Groove Type | U-Groove (round belt profile) |
| Belt Width Compatibility | 6mm or 8mm (see variant options) |
| Outer Diameter (OD) | 20 / 30 / 40 / 50 / 60 / 80mm (see variant options) |
| Bore Diameter | 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20mm (see variant options) |
| Hub / Body Thickness | See variant options |
| Shaft Fixation | Set screw |
| Finish | Natural aluminum (uncoated) |
| Quantity per Order | 1 piece |
Match the groove width to the diameter of your PU round belt. If your belt measures 6mm in cross-section diameter, select the 6mm groove variant. For an 8mm round belt, select the 8mm groove variant. Using a mismatched groove width will cause the belt to either sit too loosely (risk of derailment) or be pinched (accelerated belt wear).
Measure your motor or idler shaft diameter with a caliper. Select the bore diameter that matches your shaft exactly — for example, a 5mm motor shaft requires the 5mm bore variant. The set screw will clamp the pulley onto the shaft, so a close fit is important for concentricity and minimal runout.
The drive ratio between two pulleys is determined by the ratio of their outer diameters. For example, a 20mm OD driving pulley paired with a 40mm OD driven pulley gives a 2:1 reduction. Choose your OD based on the speed reduction or mechanical advantage your application requires, as well as the available belt wrap angle in your layout.
Yes. These aluminum U-groove pulleys are well suited for desktop CNC belt-drive axes that use PU round belts. The aluminum construction keeps rotational inertia low, and the U-groove profile maintains belt tracking. For high-speed or heavy-load CNC applications, verify that the belt tension and pulley bore fit are within the mechanical limits of your specific machine design.
Yes, these pulleys can function as idler pulleys when mounted on a fixed axle with a bearing inserted into the bore. In that configuration, select a bore diameter that matches your bearing outer diameter, and press or slip-fit the bearing into the bore before mounting on the axle. The set screw is not used in a bearing-idler configuration.
Aluminum alloy naturally forms a thin oxide layer that provides moderate corrosion resistance in dry indoor environments typical of workshop and lab use. For applications exposed to moisture, cutting fluids, or outdoor conditions, consider applying a light coating of machine oil or using an anodized variant if available. These pulleys are not rated for submersion or highly corrosive chemical environments.
Specific load ratings depend on the OD, bore size, and operating speed of your application. These pulleys are designed for light-to-medium duty drive systems such as robotics, small CNC machines, and DIY automation. For heavy industrial loads or high-speed continuous operation, consult the mechanical specifications of your belt and verify that the pulley dimensions are appropriate for the expected belt tension forces.
