January 15, 2015

Bucket Fill or Cycle Time? Which is More Important?

In today's production world, every contractor's goal is to move as much dirt as possible in the shortest time. So, which is more important: bucket full or cycle time? With an excavator, cycle time is more important, and with a loader, bucket fill is more important. The reason for this is the excavator cycles faster than the loader. Using a loader, the operator will cycle 2 to 2.5 times per minute, so bucket fill is more important. When using an excavator, the operator cycles 4 to 5 times per minute, so the operator on the excavator will maintain a constant bucket load-and-go to get a faster cycle.

Let's look at the excavator and analyze what features enhance cycle times other than the operator. There are a number of factors to consider.

  • Bucket size
  • Bucket tip radius
  • Bucket tub depth
  • Bucket width
  • Bucket teeth
  • Arm length/arm digger

Bucket Size
Bucket size is determined by lift specs, material weight, bucket weight, bucket capacity, and distance to dump bucket from excavator. Plus, the excavator's hydraulic power will be decisive in bucket working range. Sizing the correct bucket to the excavator will increase production without increasing wear to internal pins and bushings, swing bearings, hydraulic pumps, and/or undercarriage wear. Many contractors ask, "What's the biggest bucket I can put on this excavator?" Oversizing the excavator bucket will cause extra load time, swing time, and dump time, plus extra machine heat when the operator is stalling the bucket trying to maintain huge bucket loads. When using an oversized bucket, the machine becomes tippy and the operator will restrain from full bucket loads. So, the extra weight of the big bucket becomes a boat anchor hanging on the end of the arm rather than an advantage. We did a production study with two identical 450s using 4.97-cu.-yd. and 6.1-cu.-yd. buckets. The machines were digging in good dirt, sitting on a bench, loading 18 wheel belly dumps. Both operators were very good and very competitive. We timed cycles from bucket tooth penetration to bucket tooth penetration. Cycle times were 14.5 seconds for the 4.97 bucket and 18.8 for the 6.1 bucket. The increased cycle times on the 6.1 bucket were noticed in the following:

  • Bucket loading time—2.5 seconds longer
  • Swing to dump—0.9 seconds longer
  • Bucket dump—0.7 seconds longer
  • Swing to dig—0.2 seconds longer

Average load time per truck over the day was 86.4 seconds for the 6.1 bucket and 84.6 seconds for 4.97 bucket. Even with an extra cycle per truck, the excavator with the smaller bucket was more productive. In addition, according to machine Information center (MIC) data, the pumps had half as much time above 3,770 psi, helping the machine run cooler.

Bucket Tip Radius
The definition of bucket tip radius is the measurement from the center of the arm/bucket pin to the end of the bucket tooth. A long tip radius has an advantage of more bucket capacity and extra reach. A short tip radius will have an advantage with increased bucket breakout and increased arm digging force. Shorter tip radiuses are used with dense/harder materials such as rock of caliche.

Bucket Tub Depth
Bucket tub depth is the measurement from the side of the bucket edge to the deepest part of the bucket. Contractors who use short tubs are looking for a quicker bucket fill and a faster dump for truck loading. Short tubs are usually accompanied with short tip radiuses and wide buckets. Deep tubs are used for trenching to increase bucket capacity. Deep tubs are usually accompanied with long tip radiuses and narrower buckets.

Bucket Width
Bucket width is the measurement from the widest point on the bucket. This could be from outside tooth to outside tooth or from outside side cutter to outside side cutter. Width of the bucket can be sized to pipe, width of trench box, width of footing for foundations, truck capacity, truck bed width, or general digging.

Bucket Teeth
Bucket teeth are determined by the type of material to be excavated. The harder the material the more penetration force is needed. Therefore the teeth will be more pointed, like tiger teeth. For cleanup, a spade nose tooth is used, which is wide for more of a straight edge on the end of the bucket. Most of the time, contractors will use a general tooth that offers penetration and straight edge.

The arm force of a 200D LC is 22,924 lb. To check the penetration force at the tip of the tooth with a regular tooth versus a tiger tooth find the area of the tip of the tooth and measure the tip width and length. Multiply the total square inches on the tip by the number for teeth on the bucket, then divide into the arm force.

Arm Length/Arm Digger
Arm length will affect cycle time with increased arm force with shorter arms. John Deere engineering design Deere excavators with superior arm force. Operators will notice the extra power in the arm and will use the arm to load the bucket for a faster cycle. The differences between a short arm and a long arm are: Shorter arms have more crowd force, are easier to control, are easier to meter, and can use bigger buckets. Long arms have more reach and dig deeper. Underground contractors prefer long arms to reach the extra drift between cycles and handle pipe in the trench box.

On an excavator there are many perimeters to peak performance for increased productivity. Sizing the bucket (and arm) for an excavator can have a significant impact on the machine performance. A long arm and a big bucket may not be the best choice in all applications.

Five items to increase excavator productivity:

  • The correct-sized bucket for quicker cycle times
  • A short tip radius increases bucket breakout
  • Short tubs for faster bucket dump
  • Long arms are for reach and shorts arms increase arm force
  • Deere excavators are arm diggers

By Mike Boyle