Excavator boom – digging force and reach

How to use the excavator digging force calculator

Pick a starting example, then enter your own pin coordinates for the boom, arm and bucket linkage from a side-view sketch, with x towards the bucket and y up. Add the retracted and extended length, bore and rod of each cylinder, the relief and holding pressures and the link weights. Move the three stroke sliders, or click a link in the drawing and drag it, to set a posture. The orange result shows the bucket digging force available in that posture and which cylinder limits it. Use Show dimensions for the working range and Edit on screen to drag pins directly in the drawing.

Excavator boom calculator side view with the arm extended, working range envelope and digging force arrows at the bucket tip — Arm extended: the boom cylinder reaches its holding limit first.

What the calculator computes

The bucket digging force and the arm digging force follow the definitions of ISO 6015 and SAE J1179: the force at the bucket tip produced by the bucket cylinder about the bucket pin, and by the arm cylinder about the boom–arm pin, at the relief pressure. The calculation uses the effective lever arm of each cylinder, dL/dθ, so any pin layout works, including a triangular rocker in the bucket linkage. The available force then checks whether the boom and arm cylinders can hold the posture at their port relief pressure, with the link weights included. In excavator boom design this holding limit often decides the real breakout force, not the bucket cylinder.

Excavator boom calculator side view with the arm crowded in and the bucket close to the machine, bucket cylinder governing the digging force — Arm crowded in: the bucket cylinder at relief pressure governs.

Working range and linkage checks

The working range envelope covers every combination of the three strokes: maximum digging depth, reach, reach at ground level, cutting height and dump height. Below each slider, a detail view shows the drive at its own scale with the lever arm r, and the chart plots hydraulic and available force over that cylinder stroke. The bucket linkage check reports the minimum transmission angle and any dead centre within the stroke.

Bucket linkage detail with transmission angle next to the chart of bucket digging force over the bucket cylinder stroke — Bucket linkage detail and bucket digging force over the bucket cylinder stroke.

Method and limits

The method follows Dudczak, Koparki. Teoria i projektowanie, and is validated against two published attachments. Friction, dynamics and machine stability are not included. Bores, pressures and weights in the examples are estimates; replace them with your data. The free version has no limits on inputs. A Pro version with lift capacity to ISO 10567, a force map over the working range and a full calculation report is in preparation.