If your printed lines stop short of a slab edge — near perimeter walls, embeds, façade elements, or exterior framing — this article explains why the FieldPrinter holds back and how to print accurately right up to the edge. It covers edge protection height (toe kick, guardrail, or barrier), control point placement, robot stationing, and choosing the right print head.
Symptoms
- Printed lines stop short of the slab edge.
- Perimeter geometry appears offset or incomplete.
- The robot avoids the edge or changes direction sooner than expected.
- You're unsure how close the FieldPrinter can safely print to a drop-off.
Why This Happens
- The FieldPrinter uses cliff sensors and safety buffers near drop-offs to keep from driving off the edge.
- Edge protection that is too short doesn't fully solve the problem. Protection at least 2" tall keeps the robot from falling, but the robot can still back away as it nears the edge — so it prints short. It takes 7" of edge protection to print accurately right up to the line. See How Tall Should Edge Protection Be to Print Near a Slab Edge? for the full explanation.
- Control points placed toward the interior reduce accuracy at the perimeter, where it matters most.
- Leaving the print head on the default Automatic setting near an edge can limit how close ink can be placed.
How to Fix or Prevent
1. Confirm edge protection is tall enough
- Verify guardrails, toe kicks, or approved edge protection are in place along the slab edge.
- 2" minimum keeps the robot from driving off, but printing near the edge will be inconsistent.
- 7" minimum is what you need to print accurately right up to the edge — that's the height where the robot's cameras and cliff sensors sit, so a 7"+ barrier fully blocks the downward sightline and the robot stays confident at the edge.
- When edge layout matters, ask the GC or trade for 7" minimum edge protection along that slab edge before you print. The FieldPrinter will not print close to an unprotected edge.
2. Drive the robot parallel to the slab edge
- Station and orient the setup so the robot travels roughly parallel to the slab edge as it prints the perimeter.
- This reduces abrupt turns and improves line quality near the edge.
3. Manually select the print head closest to the edge
- Near an edge, don't leave the print head on Automatic. In the Dusty app, open the FieldPrinter menu, find Print Position, and select Far Left or Far Right — whichever side faces the edge. These options use the print head that extends furthest from the robot body for maximum reach.
- Position the robot so the selected side faces the edge, and run a short test print after changing the setting.
- Return to Automatic for general printing once you're past the edge-critical work. See How to Manually Select a Print Head to Print Near Edges and Obstacles for the full procedure.
5. Print perimeter geometry first
- Print edge-critical layout before interior geometry to minimize re-stationing and complete the most sensitive layout under the best conditions.
Best Practices
- Verify station error before printing so small errors don't magnify at the slab edge.
- Keep the edge area clean to maintain traction and consistent print quality.
- Limit foot traffic and vibration near slab edges during printing.
- Do not attempt to override safety behavior. Re-stationing or retries will not compensate for missing or too-short edge protection.