Case Study: Redesigning a Treadmill Bottle Holder That Kept Cracking

A gym came to us with a small part that kept failing: the bottle holders on their treadmills. Members were dropping 1.5-litre water bottles into cups that were slightly too tight, and the pressure was cracking the holders at the socket — the exact point where the cup joins the machine. We redesigned the part around a 1.5L bottle, reinforced the weak spot, 3D-printed a prototype, and it dropped straight into the console and held the bottle without stressing the joint. Here's how the project went — and why a replacement part is a chance to fix the original, not just copy it.

The problem: the same part, breaking again and again

The holders that came with the treadmills had a diameter that was a little too tight for a standard 1.5L bottle. When a member pushed a full bottle in, it wedged rather than seated — and every push and pull levered against the socket where the cup meets the machine. Over time, that repeated stress cracked the holders right at that join. Replacing like-for-like would just have restarted the same cycle.

Diagnosing why it broke

This is the part we care about most. Before modelling anything, we looked at where and why the original failed: the fracture was at the socket, and the root cause was fit — a too-tight opening turning a 1.5L bottle into a lever. So the brief wasn't "copy this cup." It was two things at once:

1. Fit — open up the diameter so a 1.5L bottle sits properly instead of wedging.
2. Strength — reinforce the socket area so it handles daily, repeated loading.

We worked from the customer's own measurements: an 11 cm top opening, a 9 cm body, and 11 cm tall — sized around a real 1.5L bottle rather than guessed.

The redesign, in Fusion 360

We modelled several versions in Fusion 360, adjusting the wall thickness and the geometry around the socket until the numbers looked right for the load. The goal was a holder that accepts the bottle easily and spreads the stress away from the single point that had been cracking. For a functional, handled part like this, material matters as much as shape — tough, impact-resistant filaments such as PETG are a natural fit (we cover why in PLA vs PETG for the Portuguese Climate).

Prototype first, then commit

We printed one prototype and tested it the way it would actually be used — with a real 1.5L bottle — to confirm the bottle seated cleanly and the socket held without flexing at the join. Only once the fit and strength were validated did the part get its final finish. This "make one, test it, then commit" step is the whole point of how the studio works: a physical test catches what a screen can't.

The result

The prototype dropped straight into the treadmill's console recess and held the bottle exactly as intended — no wedging, no stress on the socket. The customer's reaction, once it was installed, was simply: "Ficou top!" A part that had been a recurring headache became a solved problem.

Why this is the real value of a replacement part

Anyone can copy a broken part. The useful version of the job is to ask why it broke and design that out — a better fit, a stronger joint, the right material for how the thing is actually used. That's the difference between a replacement that fails again and one that lasts. It's the same design-test-refine process behind everything the studio makes.

Have a part that keeps breaking?

If you've got a component that fails the same way every time — a bracket, a clip, a holder, a discontinued piece you can't buy any more — that repeat failure is usually a design or material problem worth fixing, not just replacing. See our complete guide to custom & replacement 3D printing, our deep-dive on replacing discontinued and hard-to-find parts, or how an order works — then send us a photo and a couple of measurements.

Frequently asked questions

Can you improve a part, not just copy the broken one?
Yes — and usually that's the point. If a part keeps failing in the same place, we look at why (fit, wall thickness, material, the load it takes) and design that weakness out, rather than reproducing it.

What do you need to get started?
A few clear photos of the part (and the spot it fits into) and the key measurements. With those we can model it, and — for anything that takes real stress — prototype and test one before making more.

How long does a custom replacement take?
It depends on complexity and how many test iterations the fit needs. A reverse-engineered or redesigned part needs design and test-print time first; you'll get a timeframe once the part and brief are confirmed.

Which material do you use for functional parts?
For parts that get handled or loaded, we lean toward tougher, impact- and heat-resistant materials like PETG rather than standard PLA. The right choice depends on where and how the part is used.

Dr3amToReal is a design-led 3D-printing studio in Aveiro, Portugal, founded by Ana Sousa, who applies a quality-engineering background to product design — every piece is designed, prototyped, tested, and refined before it goes on sale. Made to order · ships within mainland Portugal.