Draining uncured resin from channels
This is the one that ruins most first chips.
A chip comes off the plate looking perfect. The channels are full of uncured resin — which is expected, and fine, as long as it comes out. It does not come out. Some of it stays. Then the part goes into the UV cure box, or simply sits in a lit room for a day, and the resin still inside sets solid.
At that point the channel is gone. There is no recovering it.
Why it is hard
Section titled “Why it is hard”Three things work against you at this scale.
Surface tension. In a 0.5 mm channel, capillary forces are strong enough to hold a column of resin in place against gravity indefinitely.
Viscosity. Standard resins are 100–500 mPa·s — a hundred to five hundred times water. Through a sub-millimetre channel that is slow.
No air path. A column of liquid in a tube with one open end does not move. Pushing at one end has nowhere to push to; pulling has nothing to let air in behind it. You need two openings, and this is the single most important fact on this page.
Design against it
Section titled “Design against it”Two-piece is the real answer
Section titled “Two-piece is the real answer”A two-piece split makes the channels open grooves until you bond the lid on. Resin rinses straight out. There is nothing to trap.
This is why two-piece is the default, and below about 0.5 mm channels it is close to the only realistic option.
If you must go monolithic
Section titled “If you must go monolithic”Ports at both ends of every path. Every channel needs a route in and a route
out. The
dead-end-channel check exists for
exactly this.
Add vents. OpenChip can plan them: the drainage planner finds the points furthest from an opening, the unreachable regions, and the blind branches, and places a hole at each. The default bore is 0.8 mm.
A vent does two jobs, and the second is the one people forget: it shortens the escape path, and it gives air somewhere to come in behind the resin.
Vents are stored in the project (drainageVents) and are yours to move, resize
or delete. You plug them afterwards with a drop of resin and a UV pen, or leave
them as extra ports.
Keep it short and wide where you can. Resistance to resin is the same fourth-power relation as resistance to water.
Avoid blind branches entirely. A pressure tap or a reservoir with one opening cannot be flushed at all. If you need one, it needs its own vent.
What the checks tell you
Section titled “What the checks tell you”Only on a chip that is actually enclosed — a two-piece split does not trigger them.
enclosed-cavity says the chip
prints sealed, and reports roughly how much resin is inside in mm³. That
number is worth looking at: it is the volume you have to get out.
It also catches the accidental case — a split height set outside the block means no cut happens and the chip prints sealed even though the split type says two-piece.
undrained-region names
specific places, with a reason:
| Reason | Means |
|---|---|
| Unreachable | No path to any opening. A vent is the only option. |
| Dead end | One closed end. Cannot be flushed at all. |
| Far from an opening | A long way along the channel from any port — the reference distance is 15 mm. |
Clearing a printed chip
Section titled “Clearing a printed chip”Work immediately. Every hour on the bench in ambient light is more cure.
- Off the plate, drain by gravity. Stand the chip so channels run downhill towards a port. Ten minutes. Free, and it gets a surprising amount.
- Flush with a syringe. Isopropanol into one port, catch it at the other. Steady pressure, not a jab — a sudden push can burst a thin wall. Repeat until what comes out is clean.
- Vacuum, if you have it. Pull from one port with the other open. More effective than pushing, because it does not pressurise the chip.
- Ultrasonic bath. The chip submerged in isopropanol, ports open, 5–10 minutes. Good at dislodging what the flush loosened.
- Check before curing. Hold it to a light. A channel with resin in it looks different from one that is clear — glossier, and the meniscus moves if you tilt it. Flush anything you are unsure about again.
Do not post-cure until you are certain. Post-curing is the irreversible step.
If a channel is already blocked
Section titled “If a channel is already blocked”Usually terminal. Two things sometimes work, both with a low success rate:
- Solvent soak. Days in isopropanol. Partially cured resin can soften enough to shift. Fully cured resin will not.
- Mechanical. Nylon monofilament or fine wire from a port, if the channel is straight and large enough. Steel wire scratches, and a scratched channel is a bubble trap.
Better to reprint. Better still to have gone two-piece.