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.

To finish a run, press Escape or Enter. Either one ends the run and leaves you in the draw tool, so your next click starts a new, unconnected path. Press V to go back to the select tool.

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.

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.

Where the cursor is

A box in the bottom-right corner of the canvas reads the pointer’s position in millimetres, and the rulers mark the same point with a crosshair.

It reports the point after snapping, so the figures name the coordinate a click would actually produce rather than where the mouse happens to be. When a snap is holding it, what caught is named alongside — endpoint, grid, or the locked angle. Hovering with the select tool there is nothing to snap to, so you get the bare pointer; while you draw, or drag a node, you get where it will land.

The coordinates are absolute chip millimetres from the bottom-left corner — the same frame as the rulers and every dimension in the inspector. A port 5 mm in from the left edge is a port at X 5.00.

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.
Select all channels in the inspector selects every segment, so you can resize them all at once.
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.

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.

Centering the design

The inspector’s Position block puts the design in the middle of the chip. With nothing selected the button reads Center design and moves everything; marquee a group of nodes and it becomes Center selection and moves only those, leaving the rest where they are.

It measures what the design occupies, not where its nodes sit. A luer-lock port is 7.7 mm across against a 0.8 mm channel, and a bezier bows outside the box its endpoints make — both are counted, so the margins either side come out equal rather than only looking equal on the centerlines.

Nothing is scaled or rotated. Every node in scope shifts by the same amount, so spacing, curves and dimension markers are untouched, and the whole move is a single undo step. The button greys out when there is nothing to correct.

Changing the chip’s Width or Length never moves your channels by itself — a feature placed hard against an edge is usually there on purpose. When a resize does leave the design lopsided, a message offers the same correction with a Center action. Ignore it and nothing happens.

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.

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