Drawing channels

You draw a channel network, not a solid. Nodes joined by segments. The block, the voids and the ports are all derived from it.

The three tools

Tool	Key	Does
Select	V	Click, marquee, drag nodes and bezier handles.
Draw	P	Click to lay down segments, one after another.
Dimension	D	Pin a channel width at a point along a segment.

Laying down a path

Press P and click. Each click adds a node and a segment back to the previous one. A rubber band shows where the next segment will go, already snapped.

Two ways to finish a run:

• Escape — ends the run and returns to the select tool.
• Enter — ends the run but stays in the draw tool, ready for the next one.

To branch off an existing network, start a new run and click on an existing node. Endpoint snapping welds the two together into one junction.

Caution

Clicking near a node is not the same as clicking on it. Two channels that end a micron apart are two channels, and the chip will print with a wall between them. Watch for the highlight that says the snap has caught, or check afterwards in the CAD tab’s X-ray view.

Snapping

Three kinds, all toggleable from the toolbar, resolved in this order — the first that catches wins.

Endpoint

Welds onto an existing node. The grab radius scales with zoom, so it stays usable whether you are looking at the whole chip or one junction.

This is the one to leave on. It is what makes a junction a junction.

Angle

Locks the segment to multiples of an angle from where the current run started. 15° by default; 45° is the other offered choice.

Only applies while drawing, since it needs an origin to measure from.

Grid

Rounds to the grid pitch — 1 mm by default. Toggle the visible grid with G; the snap and the display are separate settings.

Editing

With the select tool:

• Click a node or segment to select it. Shift-click to add.
• Drag a marquee across empty canvas to select everything inside.
• Drag a node to move it. It snaps as it goes, including onto other nodes — which is how you join two branches after the fact.
• ⌘-click a segment to insert a node, splitting it cleanly and keeping its dimension markers.
• Delete or Backspace removes the selection.

Undo is ⌘Z. A whole drag collapses into one undo step, which is what you expect when you press it.

Straight and curved

Every segment is one or the other, switchable at any time with B or from the inspector.

A bezier segment gets two control handles you can drag with the select tool.

The handles are kept when you toggle back to straight, so toggling again restores the curve exactly. Nothing is lost by trying it.

Curves matter for more than looks. Sustained curvature sets up Dean flow, which stirs the cross-section transversely — it is the whole mechanism behind the spiral mixer. A sharp corner does not do that; it just adds a little pressure drop.

Note

A bowed bezier can stray outside the chip between two perfectly placed endpoints. The boundary check walks the whole swept channel rather than just the node positions, so it catches this — see channel-near-boundary.

Copy, paste and repeat

• ⌘C copies the selected sub-path.
• ⌘V pastes. Successive pastes cascade rather than stacking, so the second is not hidden under the first.
• ⌘D duplicates in place.

The inspector’s Copy & repeat block does arrays: pick a count and a spacing and it lays out that many copies, optionally alternating direction. The canvas draws a ghost preview as you change the numbers.

Cross-section

Set per segment, in the inspector: round, rect or trapezoid.

Shape	Notes
rect	The default. Prints predictably, and pairs naturally with a two-piece split.
round	Width is the diameter; height is ignored. Lowest pressure drop for a given area.
trapezoid	Draft on the side walls. Easier to release, and closer to what a wet-etched channel looks like.

The shape changes the pressure drop by more than people expect — see Pressure drop and Hagen–Poiseuille.

What to watch

The Design checks panel updates as you draw. The three that come up most often:

• dead-end-channel — a branch that stops in the middle of the chip.
• disconnected-network — a snap you thought caught and did not.
• channels-too-close — two runs closer than the wall between them can survive.

Next

• Ports and fittings — turning ends into openings.
• Dimension markers and lofting — setting widths.
• Mixing chambers — widened volumes at nodes.