When resin parts come out with soft edges, bloated details, or slightly larger tolerances than the CAD model, most people blame the machine. More often the culprit is simple physics: UV light keeps penetrating the photopolymer a fraction beyond each layer. Understanding exposure depth turns these frustrating prints into a solved problem.
The working curve: what happens when the light hits
Every photopolymer follows a relationship between light dose and cured thickness, called the curing depth curve. Thin layers near the exposure surface cure fully, but light also bleeds sideways and continues to slightly advance the layer below. That side-bleed is why details blur and near-horizontal surfaces thicken.
| Parameter | Too low | Too high |
|---|---|---|
| Layer exposure time | Weak parts, stuck-to-film failures | Bloated details, loss of sharpness |
| Burn-in / bottom layers | Parts detach from the plate | Over-cured "elephant foot", hard to remove |
| Off / lift time | Suction pull causes delamination | Longer prints for no benefit |
The three spots that bleed
1. Lateral bleed inside the layer
Light scatters in the resin, curing slightly wider than the pixel column that emitted it. Fine positive text closes up, and thin negative gaps fill in. This is unavoidable, but it scales with exposure - so a minimal sufficient exposure keeps detail crisper.
2. Penetration into the layer below
Each new layer adds a margin that cures into the previous one. With repeated exposure, near-bottom and overhang interiors become denser and slightly oversized. This is why tall prints can drift from nominal dimensions over time.
3. Burn-in layers press deeper
Bottom layers use long exposures for adhesion. That same long exposure cures deep and wide, producing the classic "elephant foot" at the part's base - the widened, rounded first few millimetres.
A practical tuning routine
- Cut bottom layers to the minimum that still holds the part - usually 3-6 depending on geometry. More is rarely better.
- Set layer time to the lowest value that gives strong parts. Print a small exposure test with a stepped target to find it.
- Add a rest / wait period when printing large cross-sections, letting resin settle so pixels cure where they should.
- Keep resin temperature stable - cold resin needs more exposure and cures differently; a warm, mixed tank prints more predictably.
Choosing a resin that responds predictably
A consistent, well-characterised resin makes exposure tuning far easier. ANTINSKY's Standard Lite Resin is a fast, forgiving all-rounder ideal for daily prints and exposure work, while the Standard Resin is a solid high-clear workhorse. Both are available at InnoStation 3D with clearly publishable parameter ranges, so you can build a stable workflow instead of chasing a moving target between bottles.
The bottom line
Soft, bloated resin parts are not random bad luck - they are over-exposure acting through real optical physics. Dial exposure down to the minimum that holds the print, drop bottom layers, stabilise temperature, and use a consistent resin. Your details will come back.