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When your robotics build, CNC router, or maker project demands a reliable belt drive without the guesswork of mismatched components, finding the right pulley becomes a real bottleneck. These U-grooved aluminum pulleys are engineered for makers, engineers, and DIY builders who need a clean, stepless profile that grips PU round belts firmly without slipping or walking.
Each pulley is machined from aluminum alloy with a clean U-groove profile. Groove widths are available in 5mm, 6mm, and 8mm to match standard PU belt diameters. Outer diameters range from 20mm to 80mm (approximately 0.79" to 3.15"), and bore diameters span 3mm to 20mm to fit a wide range of shafts. The stepless (without step) hub design keeps the profile compact and symmetrical.
Typical use cases include small-scale conveyor belt systems for maker labs, tension-adjustable drive trains in desktop CNC machines, and lightweight transmission assemblies in educational robotics platforms where a U-groove pulley for PU round belt is the preferred drive element.
| Material | Aluminum alloy |
|---|---|
| Groove Profile | U-groove (for PU round belt) |
| Hub Style | Without step (stepless) |
| Outer Diameter (OD) | 20 / 30 / 40 / 50 / 60 / 80mm |
| Groove Width | 5mm / 6mm / 8mm |
| Bore Diameter | 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20mm |
| Quantity per Order | 1 piece |
| Surface Finish | See variant options |
| Set Screw / Keyway | See variant options |
| Max Recommended Belt Diameter | Match to selected groove width |
Match the groove width to the diameter of your PU round belt. A 5mm groove width is suited for 5mm diameter PU belts, 6mm for 6mm belts, and 8mm for 8mm belts. Using a groove that is too wide will allow the belt to shift laterally; too narrow and the belt will ride on the groove edges rather than seating fully.
Measure your shaft diameter with a caliper and select the matching bore size from the variant options (3mm through 20mm). The bore should be a close sliding fit on the shaft. If you plan to use a set screw or locking collar, choose the bore that matches the shaft exactly — do not go larger expecting to compensate with adhesive.
The speed ratio between two pulleys is determined by their OD ratio. For example, pairing a 20mm driver pulley with a 40mm driven pulley gives a 2:1 reduction (half the speed, double the torque). Choose ODs based on the gear ratio your application requires, keeping belt wrap angle and center distance in mind.
These aluminum pulleys are well-suited for light-to-medium duty applications such as desktop CNC machines, small conveyors, and robotics platforms. Aluminum alloy provides a good strength-to-weight ratio for these use cases. For heavy industrial loads or high-speed applications exceeding the design envelope of PU round belts, consult the belt manufacturer's load ratings.
Aluminum naturally forms a thin oxide layer that provides moderate corrosion resistance in typical indoor environments. 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. The oxide layer does not significantly affect belt grip or dimensional accuracy.
The U-groove profile is specifically designed for round-cross-section PU belts. It is not compatible with flat belts, V-belts, or timing belts, which require different groove geometries. Using an incompatible belt type will result in poor tracking, accelerated belt wear, and potential slippage under load.
A "with step" pulley has a raised shoulder (step) on one or both sides of the groove hub, which can act as a belt guide or allow the pulley to be positioned against a bearing face. A "without step" (stepless) pulley has a uniform hub diameter with no shoulder, making it more compact and easier to align in symmetrical multi-pulley layouts. This listing is for the stepless version.
