The Complete Guide to Excavator Feller Buncher Attachment

You are weighing whether to mount a felling head on an excavator, skid-steer, or dedicated feller-buncher chassis and need to know which cutting mechanism—disc saw, bar saw, or shear—matches your stand conditions, target diameter, and production goals. Michael J. Hartman, ISA Board-Certified Master Arborist, explains the mechanical differences, best-use windows, and hidden costs so you can match the head to the job instead of fighting the wrong tool.

Forest Operations research shows that cutting speed, fuel burn, and residual stand damage vary more by head type than by carrier brand. Understanding the physics behind each design keeps you productive and profitable on steep slopes, rocky ground, or high-value saw-timber stands.

How Felling Heads Work: Disc, Bar, and Shear Physics

A disc saw spins a 1–1.6 m steel wheel at 900–1 200 rpm. Centrifugal force stores kinetic energy so the 12–20 carbide teeth can sever a 40–50 cm stem in under two seconds. The blade is always live, so the operator only feathers the hydraulic valve; there is no startup lag. Downside: rock contact sparks ignite duff and a thrown tooth becomes a bullet.

A bar saw, by contrast, retracts the chain into a housing until the arm accumulator squeezes the stem. The 0.3 s spin-up delay is negligible, but the 80 cm maximum cut diameter is smaller than a disc. Chain tensioning is automatic, and kickback is eliminated because the nose is buried in the head frame. Maintenance costs are lower—only one bar and two sprockets to replace—but cutting time per stem rises 30 % on multi-stem bunches.

Shear heads use a curved 38–46 cm stationary blade and a hydraulic ram to push the stem past a knife edge. No spinning mass means zero fire risk and the lowest daily fuel burn—2.5 L/h versus 4–6 L/h for saws. Shears, however, leave a crushed fiber bundle that can split 30 cm down the trunk, creating a decay pocket if the tree is left as a seed tree. Shears are limited to 25 cm softwood or 20 cm hardwood.

Matching Head Type to Terrain and Stem Diameter

Rocky ground, root wads, or lava flows immediately favor bar saws because the blade retracts on every approach. Forest Service crews on the Ochoco National Forest report a 70 % reduction in fire starts after switching from disc to bar heads on basalt slopes. If your tract averages 35 cm Douglas-fir on glacial till, specify a bar head and budget the extra 0.8 h/acre cutting time.

Clear-cuts stocked with 15–20 cm lodgepole pine or pulp-size hardwood convert better to sheer heads. The ram-type cut is fastest for small diameters, and the residual stand suffers almost zero bark scuff when the accumulator arms pivot away from adjacent trees. A Michigan crew documented 1.3 h/acre production on 18 cm aspen with a shear compared with 1.8 h/acre for a disc head on the same stand.

High-value saw-timber or seed-tree stands where residual damage must be near zero call for disc heads. The one-pass cut eliminates the multiple clamp-and-release cycles that scuff cambium on neighboring trees. On a Sierra Nevada mixed-conifer shelterwood, disc heads reduced adjacent scuff from 14 % to 4 % of leave trees compared with bar heads, justifying the higher fuel burn on a 60-year rotation.

Accumulator Arm Design and Stem Security

Disc and bar heads rely on accumulator arms to hold previously cut stems while the head pivots for the next tree. Accumulator geometry—parallel arms versus curved paddles—determines how many stems can be carried before the bunch is dropped. Parallel arms on a 1.5 m head hold 6–8 lodgepole pine or 4–5 30-cm fir before the center of gravity shifts and the operator must drop the load. Curved paddles increase capacity by 20 % but raise visibility obstruction on steep side slopes.

Arm spacing also affects the maximum diameter the head can swallow without reopening. A 68 cm throat gap accepts 32 cm softwood on the diagonal; upgrading to 78 cm adds 4 cm capacity yet increases carrier width by 20 cm, a liability on narrow forest roads. Match throat gap to the average diameter plus 10 cm to avoid mid-slope bunch drops that require downhill repositioning.

Carrier Matching: Excavator, Skid-Steer, or Dedicated Feller-Buncher

Excavator mounts place the head on a 6–8 m boom, ideal for roadside or wetland buffers where the carrier must stay on firm ground. The boom’s 270° swing arc lets one parking pad harvest a 60 m corridor without moving tracks, but the 4–6 t excavator mass limits slope work to 25 %. Hydraulic flow requirement is 180–220 L/min at 28 MPa; verify the carrier’s pump and cooler can sustain 8 h of continuous saw spin without overheating oil.

Skid-steer adapters convert a 2-t platform into a short-range buncher for fuel-break or fence-line maintenance. Flow and pressure are identical to excavators, but the fixed boom limits reach to 3 m ahead of the tracks. Tire machines bog in loose pumice or snow where a tracked feller-buncher floats. Counterweight kits—400 kg of steel bolted to the rear bumper—keep the tires down on 30 % side slopes.

Dedicated feller-bunchers add 30 % more accumulator capacity and a cab roof shield against falling deadwood, but the 200 k price premium only pays on 1 000+ acre plantations. Rental rates run 1 200–1 500 per day versus 600–800 for a skid-steer adapter, so reserve dedicated carriers for week-long clear-cuts with long haul distances.

Maintenance Costs and Wear Rates

Disc saw teeth last 150–200 stems on clean grit; rock contact shortens life to 40 stems. A 20-tooth disc runs 1 800 plus 4 h labor to swap, so rock clauses in the contract add 0.60 per stem on basal till sites. Carbide teeth can be rotated once, doubling life for an extra 30 min downtime per rotation. Keep a spare 20-tooth set on the service truck to avoid 2-day freight delays from the dealer.

Bar-chain replacement cycles every 600 stems—about 5 days of production—at 240 per bar. Tensioning rags indicate worn rails inside the head; inspect weekly for galling that pinches the bar and causes side-cut drift. Chain oilers consume 1 L of biodegradable bar-oil per 8-h shift; blockages starve the nose and triple wear rate.

Shear blades require daily knife-edge honing; a 25 cm blade dulls after 50 stems of frozen cedar. Replacement blades cost 380 and swap in 30 min with one technician. Accumulator pivot pins gall in abrasive ash; grease intervals drop from 50 h to 10 h in volcanic dust.

Fire Risk and Spark Suppression

Rock strikes on a disc saw throw 3 m sparks that ignite duff at 400 °C. Forest Service fire reports attribute 14 wildfires in the Pacific Northwest to hotsaw strikes between 2015 and 2022. Mitigations include 2 L/min water mist nozzles mounted on the head, mandatory 15 m hose reels, and 6 kg dry-chem extinguishers in the cab. Operations cease when relative humidity drops below 25 % and wind exceeds 15 km/h; the same prescription that triggers chainsaw shutdowns.

Bar saws eliminate spin-on-contact sparks but the chain still throws micro-sparks during cut initiation. A magnetic debris shield around the nose reduces spark travel to 1 m, and the 0.5 s spin-up limits exposure. Shear heads generate no sparks, making them the default choice during regional fire bans when every saw must carry a suppression kit.

What to Spec on Your Next Contract

Choose a disc head when daily production exceeds 40 stems, diameters reach 45 cm, or residual stand damage premiums exceed 40 per leave tree. Specify a bar head on rocky slopes, lava, or root-bound sites where fire risk triggers shutdown clauses. Pick a shear for low-value pulp under 25 cm where fuel burn and zero spark rules outweigh speed. Match accumulator throat to average diameter plus 10 cm, verify hydraulic flow at 200 L/min, and stock a spare set of teeth or blades before the truck rolls. Finally, log actual cycle times for three shifts and adjust the bid—realized production varies 25 % from textbook tables once slope, slash, and operator experience intersect.