An excavator moves material by repeating a work cycle: dig, swing, dump, and return. Each cycle transfers one bucket of soil, rock, or debris from the cut to a truck, pile, or disposal area. The total time for one loop is called cycle time, and it strongly controls how much work the machine can complete in an hour.
Shorter, smoother cycles usually mean higher productivity, lower fuel use per cubic meter, and better coordination with haul trucks.
During the dig stage, the bucket fills as the boom, stick, and bucket curl apply force to the ground. The upper structure then swings to the dump point, releases the load, and swings back while the operator positions the bucket for the next bite. Productivity depends on bucket capacity, fill factor, cycle time, material type, operator skill, and jobsite layout.
Engineers and site managers use cycle-time estimates to choose machine size, plan truck spacing, and reduce delays.
Key Facts
- One excavator cycle = dig time + swing loaded time + dump time + return swing time.
- Cycles per hour = 3600 / cycle time in seconds.
- Hourly production = bucket capacity × fill factor × cycles per hour.
- Effective bucket volume = rated bucket capacity × fill factor.
- Shorter swing angles usually reduce cycle time because the upper structure rotates through less distance.
- Hard, dense, wet, or compacted material often increases dig time and lowers bucket fill factor.
Vocabulary
- Cycle time
- Cycle time is the total time needed for one complete dig, swing, dump, and return sequence.
- Fill factor
- Fill factor is the fraction of the bucket's rated capacity that is actually filled during digging.
- Bucket capacity
- Bucket capacity is the volume of material a bucket is designed to hold, often measured in cubic meters or cubic yards.
- Swing angle
- Swing angle is the amount the excavator upper body rotates between the digging location and the dumping location.
- Hourly production
- Hourly production is the amount of material moved by the machine in one hour of operation.
Common Mistakes to Avoid
- Using bucket capacity as the actual load, which is wrong because real buckets may be underfilled or heaped depending on the material and digging conditions.
- Forgetting to convert cycle time from seconds to hours, which gives production values that are too small or too large by a factor of 3600.
- Ignoring swing angle, which is wrong because a truck or pile placed farther around the machine can add time to every cycle.
- Assuming every cycle is identical, which is wrong because operator motion, trench depth, truck delays, and changing soil conditions all affect real cycle time.
Practice Questions
- 1 An excavator has a 1.2 m3 bucket, a fill factor of 0.90, and a cycle time of 30 s. How many cubic meters per hour can it move?
- 2 A job requires moving 540 m3 of soil. The excavator's effective bucket volume is 0.75 m3 and its cycle time is 25 s. How many hours of continuous cycling are needed?
- 3 A site manager can place haul trucks either 45 degrees or 120 degrees from the digging face. Explain which placement should improve productivity and why, assuming safety and access are acceptable.