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Overview

This upgrade replaces the stock drive system of the low-cost China rock tumbler shown in the photos.
It uses a fully printable TPU timing belt together with PLA/PETG pulleys (8.5 mm width).
The system is fixed-length, meaning the tumbler has no tensioner — the TPU belt stretches slightly and creates its own preload.

Everything is fully 3D-printed and works as a direct drop-in replacement.

Features

– Fully printable TPU timing belt
– PLA/PETG pulleys, 8.5 mm wide
– Smoother and quieter than the stock rubber belt
– Reduced speed: approx. 70 rpm instead of the original ~120 rpm
– More controlled motion = better polishing behaviour
– No tensioner needed; fixed-length belt design

How it works

This tumbler has no built-in tension adjustment.
The TPU belt is printed with a precise fixed circumference and stretches just enough to grip both pulleys firmly.

The result:
– quieter operation
– more consistent torque
– less vibration
– lower rotation speed, which improves polishing quality and reduces mechanical stress

Printing Recommendations

TPU Belt:
– TPU 95A
– 0.2 mm layers
– 20–30 mm/s
– 3–4 walls
– 100% or concentric infill

PLA/PETG Pulleys:
– 0.16–0.2 mm layers
– 4+ walls
– 40–60% infill
– PLA+ for crisp detail or PETG for durability

Installation

Print belt and both pulleys.

Mount the small pulley on the motor shaft.

Mount the large pulley on the tumbler shaft.

Stretch the TPU belt slightly and slip it in place.

Verify smooth rotation.

Enjoy the quieter, slower, more stable drive.

Included Files

– Motor pulley
– Main drive pulley (8.5 mm width)
– TPU timing belt (fixed-length)

Compatibility

Designed specifically for the common low-cost China rock tumbler
(the metal-frame single-barrel models widely sold on Amazon, AliExpress, Temu, etc.).
Not compatible with other tumbler geometries.

Thanks

If this upgrade works well for you, a Make or comment helps others tremendously.

Anyone who would like to support me is very welcome to buy me a beer.

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