GT2 idler from the printer: a build-time stopgap
Why a printed smooth idler saved the printer build
When a part is missing during the build
We know the drill: printer half built, and the one part missing from the bag is – of course – a smooth GT2 idler. Reordering means a few days of standstill. So I quickly printed one and ran the printer on it to finish the build.
Spoiler: it worked. Clean belt path, nothing walked off, the build was done. That's exactly what this part is for – a get-you-running solution, not a permanent part.
What the part is
A smooth (toothless) GT2 idler for 12 mm wide belts. Smooth means: it only guides the belt, it doesn't drive it – no teeth needed for that. Two flanges keep the wide 12 mm belt nicely centered.
- Belt: GT2, smooth, 12 mm wide
- Runs on: a 625 ball bearing (Ø 5 mm bore) on an M5 screw
- Flanges: both sides
Print & assembly
A mechanical part – so print it a bit more carefully:
- Material: PETG (more wear-resistant than PLA on moving parts)
- Layer height: 0.16 mm – finer = smoother running surface for the belt
- Walls: 4+, Infill: 60–100 %
- Supports: none – printed flat, bore vertical
- Assembly: press-fit the 625 bearing, M5 screw through
A fine layer height gives a smooth running surface (otherwise the belt rattles over the layer lines), and the bearing fit should be snug but not forced – too loose and the bearing wanders, too tight and you press it in crooked.
Did it hold up?
For the purpose: yes. The printer ran stably enough on the printed idler to finish commissioning and the first prints. No belt skipping, no walking off the roller. As a bridge until the bought metal part arrived, perfectly fine.
Let's stay honest: a printed plastic running surface wears over time and can develop play. For an idler as a bridge or an emergency spare that's okay – for permanent operation a metal idler with a proper ball bearing belongs in. Use the part to get running again, then swap it.
Conclusion
Sometimes the best thing about a 3D printer is that, in a pinch, it keeps building itself. A missing small part doesn't have to mean days of standstill – half an hour of printing, a 625 bearing in, and you're going again. The STL is on Printables:
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