Mellow GT2 20-Tooth Drive Pulley for 6 mm Belt and 5 mm Shaft

Mellow GT2 20-tooth drive pulley for a 6 mm belt and 5 mm shaft, manufactured from aluminium alloy. It transfers motor rotation to a 2 mm-pitch timing belt, providing a theoretical belt travel of 40 mm per pulley revolution.

The 7 mm-wide toothed track provides clearance for a 6 mm belt, while the side flanges help guide its path. The hub has two radial set screws to secure the pulley to the shaft.

What distinguishes this Mellow pulley

Mellow emphasises tooth machining and belt engagement. According to the manufacturer, this family is produced using tooling supplied by Gates and achieves a surface finish of Ra 0.4 µm. This is a Mellow-brand pulley: the statement about manufacturing tooling does not make it a Gates-brand pulley.

Surface roughness describes the finish, not dimensional tolerances or the printer's final accuracy. A well-machined tooth profile supports consistent belt contact, but the result also depends on alignment, tension and the condition of the complete transmission.

• 2 mm-pitch GT2 profile: engages a matching belt for synchronised motion transmission.
• Aluminium body: a lightweight construction for compact drives.
• Two fixing points: secure the pulley position on the shaft.
• 7 mm track: the version designed for a 6 mm belt.

Dimensions and specifications

Dimensions are nominal. The 15 mm measurement is the flange outside diameter and must not be used to calculate belt travel.

Compatibility and related components

Suitable for Cartesian or CoreXY 3D-printer drives, plotters, laser engravers and other mechanisms designed around a 6 mm GT2 belt and a 5 mm shaft. It can also fit many NEMA 17 motors with this shaft diameter; check usable shaft length and available clearance, as the NEMA 17 mounting format alone does not guarantee compatibility.

It can be used with the 6 mm wear-resistant GT2 belt. For a return path contacting the smooth belt back, the Mellow smooth idler for a 6 mm belt is a related component, provided its mounting diameter and support clearance match the design.

This is not a bearing-mounted idler. It is not interchangeable with 1.5GT or HTD profiles of a different pitch, or with pulleys for an 8 mm shaft. On a CoreXY machine, retain the tooth profile and tooth counts specified by the drive design.

Project reference: the Voron 2.4r2 uses 20-tooth GT2 pulleys for 6 mm belts in its A/B drives. This pulley matches the profile, tooth count and 5 mm bore; before choosing it, check that its 16 mm overall height and track position fit your assembly's parts and spacing.

Installation

1. With the machine switched off, check the 5 mm bore and shaft and ensure sufficient shaft length to secure the hub.
2. Position the track in line with the belt path, leaving clearance from the motor and mounting bracket.
3. If the shaft has a flat, place one set screw against it. Tighten both fixings without damaging their sockets.
4. Align the transmission before tensioning. Do not rely on continuous flange contact to correct misalignment.
5. Check the travel by hand, then run a low-speed test to verify the fixing and absence of rubbing.

Belt travel and firmware configuration

With direct drive, one motor revolution moves 40 mm of belt. For a 1.8° motor at 16 microsteps, the calculation is 200 × 16 / 40 = 80 steps/mm. A 0.9° motor at 16 microsteps requires 160 steps/mm. Internal driver interpolation does not change the configured microsteps sent by the firmware.

The following examples apply only to an axis driven directly by this pulley. Do not apply them to an extruder, leadscrew or geared transmission without adapting the calculation.

• Marlin: for an X axis with a 1.8° motor at 16 microsteps, use M92 X80. Save with M500 if EEPROM is enabled.
• Klipper: use rotation_distance: 40 in the appropriate motor section. Set microsteps and full_steps_per_rotation for the actual hardware; account for gear_ratio if a reduction is present.
• RepRapFirmware: under the same conditions as the Marlin example, set M92 X80 in config.g, consistent with the microstepping configured using M350.

Replacing another 20-tooth GT2 pulley while retaining the transmission does not require changing these parameters just because the pulley is new. Changing from 16 to 20 teeth increases travel from 32 to 40 mm per revolution and requires recalculation.

This is for you if

You need a Mellow drive pulley with defined dimensions for a 6 mm GT2 transmission and 5 mm shaft, with fitting and belt-travel information to help prepare the project.

This is not for you if

You need a roller that turns freely on a bolt, a track for a 9/10 mm belt, another shaft diameter or a replacement with a different geometry that has not been checked.

Frequently asked questions

Is 7 mm the belt width?
No. It is the nominal track width. This version is designed for a 6 mm belt.

Will a new pulley eliminate vibration?
Machining is one part of the transmission; also check tension, alignment, fixing and overall rigidity.

Are a motor or belt included?
No. One pulley is supplied; the motor and belt are purchased separately.

Contents: one Mellow GT2 20-tooth drive pulley for a 6 mm belt and 5 mm shaft.