G0 vs G1: Rapid Positioning and Linear Feed Moves

G0 (rapid positioning) and G1 (linear feed) are the two most common commands in any G-code file — usually 90%+ of all lines. Both move in a straight line to the target; the difference is why and how fast:

• G0 — get there as fast as the machine allows. For moving around the work: up to safe height, over to the next feature, back to the tool change. The machine ignores your F word and uses its own maximum rates.
• G1 — move at the programmed feed rate (F), because the tool is in (or entering) material and the cutting physics matter.

G90 G54 G17 G21      ; absolute, work offset 1, XY plane, mm
G0 Z5                ; rapid to safe height
G0 X20 Y10           ; rapid over the start point
G1 Z-3 F150          ; plunge into the stock at 150 mm/min
G1 X80 F600          ; cut a straight line at 600 mm/min
G0 Z5                ; retract — rapid again

Both are modal: after a G1, every following coordinate-only line is another feed move until G0, G2, G3, or a cycle changes the mode. The F word is modal too — set once, it persists until changed.

#The dogleg trap

The most misunderstood thing about G0: on many controls it is not coordinated. Each axis runs at its own maximum speed, so a rapid from X0 Y0 to X100 Y20 may run both axes at full speed until Y arrives, then continue in X alone — an L-shaped path, not the diagonal you drew in your head. LinuxCNC does coordinate rapids in a straight line; FANUC's default (and many Mach setups) dogleg.

The safe pattern is the one every CAM post uses:

1. Retract Z to clearance height.
2. Rapid X/Y over the target.
3. Rapid Z down to a small gap above the stock.
4. G1 the rest of the way in.

Simulating the program first shows you exactly where the rapids run — a dogleg through a clamp is easy to spot in 3D and expensive to discover on the machine.

#Common mistakes

• Plunging on G0. Posting a rapid straight down into the stock ends tools. The last hop before material contact should always be a feed move.
• No feed rate on the first G1. Controls either error out (GRBL) or use a stale/default feed — both bad. State F explicitly.
• Feed too low on rapid-height moves. The opposite waste: programs that do every move as G1 F100, turning a 30-second job into 10 minutes. Traverse moves between features belong on G0.
• Forgetting G0/G1 are modal. A bare X50 line inherits the previous motion mode. After a canned-cycle cancel or tool change, restate the mode instead of trusting whatever came before.