Plain bore, runs on shaft or pin
- Lowest part count and cost on light rollers
- Fit changes with resin moisture and temperature
- Lubricated acetal grades help dry running bores
Molded part guide: rollers
Injection Molded Rollers
A roller looks like a simple disk until the conveyor skips, the belt walks, or the shaft binds. Roundness, bore size, and where the gate sits on the tread usually matter more than the resin datasheet.
The job
The running surface and the bore have to stay true
Rollers, pulleys, idler wheels, and guide wheels share the same molding problems.
A molded roller carries load through a shaft or bearing in the bore and transfers motion on the outer tread. If the tread is out of round, belts flutter and conveyors vibrate. If the bore is oval or tapered, the shaft heats up and the wheel walks off the track.
Plastic rollers are usually acetal or nylon for wear and low friction, sometimes with PTFE modification where grease is not allowed. Nylon is tougher under shock but picks up moisture, which changes bore fit. Acetal stays closer to size in humid plants, which helps shaft clearance stay predictable.
The mold is a round cavity around a core. Gate location, cooling symmetry, and whether the part stays on the cavity or the core on ejection decide how much roundness error you see on first shots.
Resin
Picking resin for a molded roller
Starting points. Load, speed, mate surface, and environment set the grade.
| Resin | Where it fits | Watch for |
|---|---|---|
| Acetal (POM) | Light rollers, pulleys, and guides in dry or humid air | Notch sensitive at sharp hub corners |
| PTFE-lubricated acetal | Shaft or pin runs directly in the bore without grease | Lower strength than unfilled acetal |
| Nylon | Impact loads and rough handling on carts and machinery | Bore grows with moisture uptake |
| Glass-filled nylon or PBT | Higher load on a wide tread or flanged roller | Anisotropic shrink can oval the bore if fill is one-sided |
| TPU or TPE tread | Grip or noise reduction on a hard hub, often by overmolding | Overmolding adds a second molding step and bond design on the hub |
Tooling
Gate and core choice set roundness
Rollers punish asymmetric fill.
- Gate into the hub face or the bore edge, not into the tread that touches the belt
- Balanced cooling around the core keeps bore round as the part shrinks onto it
- A thick hub and thin web tread need careful packing to avoid sink on the running face
- Call runout and bore fit on the drawing so inspection matches how the roller is used
Bore
Plain bore on a shaft or bearing pressed in
The bore drives assembly and heat at speed.
Metal bearing or bushing insert
- Stable fit and higher speed before heat builds up
- Insert molded or pressed after molding
- Bore diameter must hold concentricity to the tread
Drawing
What to send with a roller design
Include how the roller is loaded and what it runs against.
Tread diameter, width, and any crown or flange profile
Shaft or bearing part number and desired fit
Load, speed, and mate surface: belt, rail, floor, or cable
Environment: washdown, humidity, chemicals, or temperature
Runout or wobble limit if the assembly is sensitive to vibration
Whether a soft tread or overmold is required for grip or noise
Keep reading
Related guides
Materials, round parts, and assembly methods.
Acetal (POM)
Default resin for low-friction rollers.
Acetal (POM)Lubricated POM
Dry-running bores and treads.
Lubricated POMAcetal vs nylon wear
Pairing roller to mate material.
Acetal vs nylon wearInsert molding
Bearings molded into the hub.
Insert moldingOvermolding
Soft tread on a rigid wheel.
OvermoldingGD&T for molded parts
Runout and bore callouts.
GD&T for molded partsGears
Another round part where runout matters.
GearsWarpage
When a wide tread dishes or rocks.
WarpageMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded rollers
Can you hold bearing-grade roundness in plastic?
Molded rollers can be held to tight runout when the drawing specifies it and the gate and cooling support it. Extreme precision often needs a secondary bore finish or a metal bearing insert.
Why does our roller wobble after molding?
Common causes are an off-center gate on the tread, uneven cooling, or the part sticking asymmetrically on ejection. Measuring runout on first shots shows whether the fix is gate, core, or ejector layout.
Is this the same as a caster wheel assembly?
This guide is the molded wheel or roller body. A full caster with fork, spring, and mounting plate is a larger assembly topic. Send the wheel CAD you need molded.
Can the tread be overmolded rubber?
Yes, when the hub and tread resins suit overmolding. Send both materials and the bond surface in CAD.
Next step
Quote the roller with bore and tread datums
Upload CAD with shaft or bearing fit and how the tread is loaded. DFM feedback covers gate location, hub stiffness, and roundness risk.