Will it hold? Simulation explained

Before you print a hook, a bracket or a shelf, you can ask Solid Vibes whether it is strong enough. Type the question the way you would ask a friend:

• “Will this hold 5 kg?”
• “How strong is this hook?”
• “Will it break if I hang a 3 kg bag on it, printed in PETG?”

You get one sentence back, for example “Yes — safety factor 3.2 in PETG. The weakest spot is where the arm meets the plate.”, a stress heatmap on the model and a small result card. Nothing about your design changes.

What the answer means

Safety factor is how many times stronger the part is than it needs to be at its weakest spot. 1 means the material starts to give way under exactly that load. Solid Vibes says:

Ask “How strong is it?” without a number and you get the load at which it starts to give way, plus a safe working load with a margin of 2.

How it decides where the load goes

The agent looks at the shape and assumes the obvious use: a wall hook is screwed on through its back plate and the weight hangs on the hook, a stand rests on its bottom face and the load sits on top, gravity pulls down. If you select a face first and ask “will this hold 5 kg?”, the load goes on that face. The answer always says what it assumed. If that's not how you use the part, tap Change load / fixtures.

Reading the heatmap

The colours show stress (von Mises, in MPa): blue is relaxed, red is the most stressed spot. The legend shows the scale and a line for the material's yield strength — the stress at which it stops springing back. The marker shows the highest stress. Switch on Deformed shape to see how the part bends; the movement is exaggerated so you can see it, and the slider sets how much.

The heatmap hides itself as soon as you change the design, because it no longer describes the part. Ask again (or press Run simulation) to update it. Reopening the Thing offers the last result for each piece.

Materials, and why printed parts are weaker

The material comes from the piece (PLA by default) unless you name one in the question. The library has real properties for PLA, PETG, ABS, ASA, PC, TPU, nylon, standard resin, aluminium 6061, steel, stainless steel, brass, walnut, plywood and acrylic.

FDM prints are built in layers, and layers bond more weakly than the plastic itself — typically 30 to 50 % weaker when pulled apart. Where the stress pulls across the layers (in the print orientation from Make), the check uses that lower strength and tells you so. Printing the part on its side often makes it much stronger.

Pro mode

Open Simulate… from ⌘K (or Change load / fixtures on the result card, or Make → Check → Simulate in Build) to set up the case yourself:

• Held still: click Pick faces, then click the faces that are screwed, clamped or resting on something.
• Loads: a weight (kg, pulled by gravity), a force (N, any direction) or a pressure (MPa, pushing into the faces) on the faces you pick. Add more loads if needed.
• Mesh: from Preview to Finest. Finer is more accurate around thin walls and sharp corners and takes a few seconds longer.
• Export: the key numbers as CSV, the whole run as JSON, and a PNG of the heatmap with its legend.

Plans and credits

Each run uses 10 AI credits (see Credits explained). On the free trial, runs are a coarse preview. Maker runs at standard resolution and can change the load amount, direction and material of a check. Pro mode — choosing your own fixtures and loads, the fine mesh steps and export — comes with Pro and Team.

What it is, and what it isn't

It is a quick linear static analysis (finite elements on a fine grid of small cubes, solved in a few seconds on our servers). It is good at telling you whether a part is in trouble and where. It is not a guarantee:

• Plastics creep under a constant load (especially PLA when warm), and print quality varies.
• Very large bending, snapping clips, impacts and vibration are outside a linear static check.
• Sharp inside corners concentrate stress; the check judges stress over about 1 mm around each spot so corners don't produce meaningless spikes. Adding a fillet there is the classic fix — ask the agent to “round the inside corner where the arm meets the plate”.

For parts that matter, aim for a safety factor of 2 or more, print one and test it.