- Stock: 20
- Model: MELLOW-IDLER-6-5
The Mellow smooth idler pulley for 6 mm belts combines a CNC-machined aluminium body with two ball bearings and an internal brass core. It is designed for builders who also pay attention to the guiding points in their belt drive: consistent motion depends not only on the motors and belts, but also on how the idlers rotate and support the belt along its path.
This variant has a 5 mm bore and an overall height of 10 mm. Its smooth running surface guides the back of a toothed belt without meshing with the teeth, in 3D printers and other mechanisms whose design accommodates these dimensions.
What its construction offers
- Careful CNC machining: supports consistent geometry and a well-finished belt contact surface.
- Two-bearing support: the two support points help keep the pulley body stable under the belt load.
- Brass core: adds internal support rather than leaving an empty central space between the bearings.
- Compact 15 mm flanges: define the sides of the running surface without taking up the space of a pulley with larger-diameter flanges.
Why idler machining matters
An idler does not set the drive ratio, but it is part of the path that guides the belt. An eccentric running surface or uneven support can introduce changes in tension and unnecessary loads during each revolution. This is why running-surface concentricity, edge finish and stable bearing seats matter.
The quality machining of this Mellow family supports more consistent guidance and helps prevent the idler from becoming a source of irregularity in a properly assembled drive. Final motion accuracy still depends on the whole system: alignment, tension, supports, motors and belt. A well-built idler is valuable without replacing every other component, but a single pulley cannot be credited with eliminating every print defect.
Two bearings and a brass core
The two ball bearings support rotation at opposite ends of the body. Between them, an internal brass sleeve adds support in the central area. This construction detail is not visible in an exterior photograph, but it distinguishes the reference beyond its bore and belt width.
The core can provide backup support in certain bearing deterioration scenarios and help retain pulley guidance. This does not mean that every failure allows normal operation with unchanged smoothness or accuracy: rough rotation, play or binding calls for inspection and replacement of the affected component. It is a construction safeguard, not a substitute for maintenance.
Dimensions of this variant
| Feature | Specification |
|---|---|
| Brand | Mellow |
| Type | Smooth idler pulley, without teeth |
| Nominal belt width | 6 mm |
| Mounting bore | 5 mm |
| Overall height | 10 mm |
| Nominal space between flanges | 7 mm |
| Flange outside diameter | 15 mm |
| Body | CNC-machined aluminium |
| Rotating support | Two ball bearings |
| Internal core | Brass sleeve |
The nominal 7 mm running width provides clearance for a 6 mm belt. This is the 10 mm overall-height version: when replacing a shorter idler, check support spacing and spacer positions. The dimensions shown are nominal values, not manufacturing tolerances.
Applications and compatibility
Suitable for belt guiding or return points in Cartesian and CoreXY 3D printers, provided the assembly accommodates a 5 mm bore and this variant's dimensions. Check belt width, overall height, running-surface position and flange diameter together.
Some compact VzBoT assemblies, for example, specify the Mellow variant and warn that an idler with 18 mm flanges will not fit. This illustrates why 'for 6 mm belts' alone does not establish compatibility: check the support and the particular project revision.
A smooth contact surface has no tooth pitch of its own. Mellow includes this idler type in 2GT and 1.5GT drives, but use must respect the belt contact face, routing and minimum bend diameter. It does not replace a motor drive pulley or a toothed idler where the design requires tooth engagement.
Installation for smooth rotation
- Check available height and align the running surface with the other pulleys.
- Use a suitable 5 mm shaft or cylindrical mounting section; avoid using threads as a bearing support surface where the design allows a smooth shaft.
- Fit the spacers required by the support. Tightening must secure the assembly without pressing against the flanges or preventing rotation.
- With belt load removed, check smooth rotation and clearance from the support.
- Apply the tension specified for your drive and recheck alignment. Excessive tension increases bearing load; it does not correct misalignment.
Mellow: mechanical development for 3D printing
Mellow develops mechanical and electronic components for 3D printers. Its NF team works on hotends, extruders, structures and transmission systems, while FLY focuses on controller boards and electronics. In its pulleys, the mechanical approach is reflected in CNC manufacture and details such as dual bearing support and the internal sleeve.
Related belt
For a GT2 drive of this width, see our 6 mm wear-resistant GT2 belt. Also check the belt's bending requirements and the intended routing in your assembly.
Frequently asked questions
Does a smooth idler change motor steps or travel distance?
No: it is not the pulley transmitting motor rotation. Replacing only an idler with an equivalent part, while retaining the driving transmission, does not change the drive ratio. Check routing and readjust tension if the assembly geometry changes.
Why do some listings call it 20T when it has no teeth?
The name is used to group sizes or variants within a product family. This reference has a smooth surface: it does not have 20 teeth, and its name must not be used to calculate a drive ratio.
Does the brass core make the bearings unnecessary?
No. It provides additional support; the bearings still handle normal rotation. Keeping them in good condition preserves smooth, accurate belt guidance.
Is it right for you?
It is for you if you want a branded smooth idler with careful machining, two bearings and a brass core, and your assembly accommodates a 6 mm belt, a 5 mm bore and 10 mm overall height.
It is not for you if you need a motor drive pulley, a toothed idler or a replacement with a different height or flange diameter.
