Plain-English definitions for the terms that come up buying and running compact excavators.
A
Angle blade — A dozer blade that can be angled to cast material to one side. Available on some machines as an upgrade over a straight blade.
Arm (dipper, stick) — The section between the boom and the bucket. Arm length determines reach and dig depth; longer arms trade breakout force for reach.
Arm force (dipper force) — The force generated by the arm cylinder pulling the bucket through material. Lower than bucket breakout force but important for sustained digging passes. More →
Auxiliary hydraulics — Circuits that power attachments. First auxiliary typically runs a hammer or thumb; second auxiliary runs rotation or additional functions. Confirm what's plumbed before buying.
B
Blade (dozer blade) — The front blade used for backfilling, grading, and stabilizing the machine while digging. Nearly universal on mini excavators.
Boom — The main lifting arm from the house to the arm. Some machines have a swing boom that offsets laterally.
Boom offset (swing boom) — The ability to swing the boom left or right independently of the house. Lets you dig parallel to a wall or fence without repositioning — a significant tight-site capability distinct from tail swing.
Breakout force — How hard the machine pushes the bucket through material. Determines performance in hard clay, hardpan, and compacted fill. More →
Bucket — The digging attachment. Comes in widths and types: digging, grading, trenching, ditching.
Bucket capacity — Volume, typically in cubic yards or feet. Heaped and struck capacities are different measurements.
C
Cab — Enclosed operator station with heat and usually air conditioning. Contrasts with canopy. Costs more, worth it for year-round work in hard climates.
Canopy (ROPS canopy) — Open operator station with an overhead protective structure. Cheaper, better visibility, no climate control.
Coupler (quick coupler) — Mechanism for changing buckets and attachments without pinning by hand. Manual or hydraulic. A hydraulic coupler pays for itself if you change attachments often.
Counterweight — Rear mass balancing the boom and load. Its position defines tail swing configuration.
Cycle time — How long a complete dig-swing-dump-return sequence takes. A major determinant of production rate.
D
Dig depth (maximum digging depth) — How far below ground level the bucket reaches. The spec most tied to size class. More →
Dipper — See arm.
Dozer blade — See blade.
Dump height — Maximum height of the bucket pin at dump. Determines whether you can load a truck or container.
E
Expandable undercarriage (variable-width tracks) — Tracks that retract for access and extend for stability. Genuinely useful when you're caught between gate width and working stability.
F
Final drive (travel motor) — The hydraulic motor and gearbox driving each track. Oil changes are frequently forgotten and failure is expensive.
G
Grading bucket (ditching bucket) — Wide, smooth-edged bucket without teeth, for finish grading and cleanup. Doesn't penetrate hard ground.
Ground pressure — Machine weight divided by track contact area, in PSI. Determines turf and soft-ground capability.
H
House (upperstructure) — The rotating portion carrying the engine, cab, and boom.
Hydraulic thumb — An opposing jaw working against the bucket to grip material. Close to essential for most work — brush, rock, pipe, debris. Hydraulic thumbs adjust under power; mechanical thumbs are set by hand.
L
Long arm (extended dipper) — Optional longer arm adding dig depth and reach at the cost of breakout force and lift capacity.
Lift capacity — How much the machine can lift, varying with reach, height, and whether the load is over the front or the side. Ask for the lift chart, not a single number — over-the-side capacity is typically lower.
O
Offset boom — See boom offset.
Operating weight — Machine weight ready to work. The basis for size class naming — a "3-ton" machine weighs approximately three metric tons. More →
P
Pins and bushings — The pivot joints throughout boom, arm, and bucket. Wear here is the most common source of front-end slop on used machines, and greasing is what prevents it.
Pilot controls — Hydraulic pilot-operated joysticks. Smoother and lower-effort than direct mechanical linkage.
Q
Quick coupler — See coupler.
R
Reach (maximum digging reach) — How far from the machine you can dig at ground level. Frequently more limiting on real jobs than dig depth.
Reduced tail swing — Configuration where counterweight overhang is minimized but not eliminated. Between conventional and zero. More →
Ripper — A single-tooth attachment concentrating all force on one point. Penetrates hardpan, frozen ground, and light rock that a bucket can't.
Rubber tracks — Standard on most mini excavators. Lower ground pressure, no pavement damage, wear faster in abrasive conditions than steel.
S
Slew (swing) — Rotation of the house on the undercarriage. The capability that fundamentally distinguishes an excavator from a loader.
Slew bearing (swing bearing) — The bearing the house rotates on. Play or noise indicates a major and expensive repair — check it carefully on used machines.
Slew lock (swing lock) — Mechanism preventing house rotation. Engage it for transport.
Steel tracks — Longer life in rock and demolition, but damage pavement and turf. Rubber pads over steel are a middle option.
Swing boom — See boom offset.
T
Tail swing — How far the counterweight extends past the tracks during rotation. Conventional overhangs substantially; reduced minimizes it; zero keeps the tail within track width. More →
Thumb — See hydraulic thumb.
Tilt bucket — A bucket that tilts side to side hydraulically, allowing sloped grading without repositioning. Excellent for ditches and finish grading.
Track shoe — The individual segment or pad on a track.
Travel motor — See final drive.
Trench box (trench shield) — A protective structure preventing trench collapse. Required, along with shoring or sloping, at 5 feet and deeper under OSHA's excavation standard.
U
Undercarriage — Tracks, rollers, idlers, sprockets, and frame. The most expensive wear system on the machine, and the first thing to check on anything used.
Z
Zero tail swing — Configuration where the counterweight stays within track width during rotation. Lets you work against walls and fences. More →
Terms That Cross Over From Loaders
If you also run a mini skid steer, these apply to both:
Auxiliary hydraulic flow — GPM delivered to an attachment. Along with pressure, determines attachment performance.
Hydraulic horsepower — (GPM × PSI) ÷ 1,714. The power actually reaching an attachment's motor.
Ground pressure — Weight over contact area.
811 — The call-before-you-dig service. Required before any excavation. Marks public utilities to the meter only — private lines are the owner's responsibility.
Competent person — OSHA-defined role required on excavation work; must inspect daily and has authority to remove workers from hazards.