Design intent, explained
Design intent is the plan behind a model: which sizes drive the others, what stays centred, what must never change. Build it in and the part updates the way you expect. Leave it out and the next edit breaks it.
Two parts that look the same
Take a plate with a hole in the middle, modelled two ways:
- Version A: the hole is dimensioned 50 mm from the left edge. Make the plate 140 mm long and the hole stays 50 mm from the left. It's no longer centred.
- Version B: the hole is tied to the plate's centre, with the sketch centred on the origin. Make the plate 140 mm long and the hole is still in the middle.
Both rebuild without errors and look identical. Only B captures what the designer meant: the hole is centred. That's design intent, and it only shows up when someone changes something.
Where intent lives in SolidWorks
| Tool | What it captures | Example |
|---|---|---|
| Sketch relations | Geometric rules | Midpoint, Symmetric, Equal, Collinear, Tangent |
| Dimensions | What's measured from where | Dimension a hole from the centre line, not from an edge that may move |
| Origin and planes | The part's frame of reference | Centre the base sketch on the origin, so mirrors and symmetry come free |
| End conditions | How a feature reacts to size changes | Through All for a through hole, not a blind depth that matches today's thickness |
| Equations and global variables | Rules between sizes | Wall = Height / 10 |
| Feature order | What depends on what | Fillets after the features they round; pattern the feature, not its sketch |
| Configurations and design tables | Families of sizes | One file for the M6, M8 and M10 versions |
Good habits
- Fully define sketches. Blue geometry can move when something upstream changes.
- Relate to the origin and the main planes, not to edges that might change.
- Use a relation when the rule is geometric. Equal, symmetric and centred say more than two matching numbers.
- Name what matters. "Wall Thickness" beats D1@Boss-Extrude1 for the next person, and for you in six months.
- Pick end conditions that say what you mean, such as Through All for a through hole.
- Keep fillets and cosmetic features late in the tree.
- Test it. Change the main sizes up and down and rebuild. If something breaks, fix it now, not when a customer asks for a longer one.
How Caddie helps
Base Profile controls the part’s footprint: D1@Base Profile is 60 mm and D2@Base Profile is 40 mm. Boss-Extrude1 controls its thickness through D1@Boss-Extrude1, currently 25 mm.
Those are the three main overall-size controls; Mounting Hole controls the cut, not the outside size.
Notice the last one: when there's more than one dimension it could mean, Caddie confirms which before linking anything.
The stress test
The best check of design intent is to change things and see what breaks. Since version 0.3.1 Caddie can do that on the open part: it makes each driving dimension 20% bigger, then 20% smaller, rebuilds after each change, lists every feature that fails or warns, and puts every value back. On a test part it checked 17 dimensions in under 7 seconds. The graphics and the tree pause while it runs, and nothing is saved.
Mostly, but Mounting Hole breaks when the 40 mm base dimension is reduced by 20%. The other five driving dimensions handled both increases and decreases, and all original sizes are restored.
Base Profile is fully defined, which is a good foundation. I couldn’t inspect the hole’s references, so the next check is whether its position should follow the plate centre or stay a fixed distance from an edge. Which do you intend?
It works on parts, up to 20 driving dimensions or 30 seconds per run. Close any open sketch first.