A forestry attachment looks inexpensive next to the excavator it hangs from, and that is exactly why so many are bought badly. The purchase price is visible and negotiable; the wear parts, the finance, the carrier hours it consumes and the hours it sits on a stand are not. A contractor who knows the true cost per stump, per hectare or per tree can price with confidence, choose between a shear and a mulcher on evidence, and tell when a second attachment for the same carrier pays. This guide sets out the cost layers, the arithmetic that turns them into a unit cost, and the one variable that outweighs all the others.
Ownership rule
Cost the attachment and the carrier as one system, per productive hour, then divide by the units that hour produces. An attachment that is cheap to buy and slow to work is expensive; an attachment that costs more and doubles the carrier’s paid hours is cheap.Fixed costs: what you pay whether or not it works
Fixed costs accrue by the calendar. Purchase price, or the finance repayments and interest that stand in for it, is the obvious one. Insurance on the attachment itself is small but real, and it should be checked against the policy on the carrier, because attachments are sometimes excluded or under-declared. Depreciation is the fall in value from the delivered price to the eventual resale price, spread across the years of ownership; for a well-supported brand with Australian parts backing it is slower than for an orphan, which is why residual value belongs in the calculation rather than being treated as a windfall at the end. None of these costs changes with the hours worked, which is what makes utilisation so powerful: the same fixed sum is spread across 300 hours or 1,200 hours, and the per-hour figure moves accordingly.
Variable costs: what you pay per hour of work
Variable costs accrue with use, and they are the layer buyers most often underestimate. The list differs by family, from blades and pivot hardware on a tree shear to the teeth, holders, bearings and belts on a forestry mulcher; wear parts to price before buying sets out what to ask for in each. What the cost model needs from that list is two numbers per consumable, a cost per replacement and a life in hours, because dividing one by the other gives the cost per hour that should be recorded against every attachment in the fleet. Rock contact, dense hardwood and dry abrasive soil all shorten wear life in Australian conditions, so the hours figure should come from local experience or a paid trial rather than from a European brochure.
Carrier-related costs: the layer that dwarfs the attachment
The carrier is where the money goes. Fuel, undercarriage wear, hydraulic oil and filters, cooling-system maintenance and the operator’s wages and on-costs are all consumed by the attachment’s working hours even though none of them appear on the attachment invoice. Transport to and from each site is a carrier cost too, and for an attachment that moves the carrier between short jobs it can be the largest single line (see transport and mobilisation). A continuous-duty head such as a mulcher or stump grinder loads the carrier’s hydraulic system harder than bucket work does, which shows up as fuel burn, oil temperature and cooler maintenance, and that difference should be reflected in the hourly carrier figure used for that attachment rather than borrowing the figure used for excavation. The hydraulic cooling and heat guide explains why.
The arithmetic: from annual cost to cost per unit
The method is the same for every attachment on this site, and it is two steps.
Use productive hours, not clock hours. Time spent tracking between stems, changing blades or waiting for trucks is still paid for but produces nothing.
This is the number to compare against the tender rate and against an alternative method.
The result is a figure that can be compared directly with a tender rate, with a subcontractor’s quote, or with the cost of doing the same work by another method: bucket removal against a stump cutter, chainsaw crew against a grapple saw, mulching in place against shearing and chipping. The cost-per-unit calculator performs the calculation for any combination of inputs, and the tender rate guide shows how the unit cost flows into a price.
An illustrative example
The figures below are round and hypothetical, chosen to show the mechanism rather than to represent any real attachment or market price.
Assume a stump grinder is bought for $40,000 and is expected to be worth $16,000 after four years, giving $6,000 a year of depreciation. Assume finance and insurance add $3,000 a year, so fixed costs are $9,000 a year. Assume wear parts and service run at $15 per productive hour and the carrier, fuel and operator run at $180 per hour. Assume the attachment works 400 productive hours a year and removes six stumps per productive hour.
The annual system cost is $9,000 plus (400 × $15) plus (400 × $180), which is $9,000 plus $6,000 plus $72,000, or $87,000. Divided by 400 hours that is $217.50 per productive hour, and divided by six stumps per hour it is about $36 per stump. Now keep every other number the same and lift utilisation to 800 hours. The annual system cost becomes $9,000 plus $12,000 plus $144,000, or $165,000; per hour it is $206.25; per stump it is about $34. The attachment’s own fixed cost has halved per hour, but the per-stump figure has moved only modestly, because the carrier dominates the total. The lesson is twofold: the carrier cost is what the attachment has to justify, and the attachment justifies it by producing more units per hour, not by being cheap.
Utilisation is the master variable
Every fixed cost in the model is divided by hours, so hours decide whether the purchase makes sense. An attachment used 150 hours a year carries its full annual finance, insurance and depreciation on very few units, and it will almost always lose on paper to hiring or subcontracting. The same attachment at 600 hours can be the most profitable item in the fleet. That is why the buying decision on this site keeps returning to annual hours, and why the hire versus buy guide treats utilisation as the threshold question.
There is a second, less obvious effect. An attachment that lets the carrier keep working when the bucket work runs out raises the carrier’s utilisation, and the carrier’s fixed costs are far larger than the attachment’s. If fitting a shear, grapple or grinder lets a $250-per-hour excavator sell another 300 hours a year, that is $75,000 of additional revenue capacity, which can justify an attachment on carrier utilisation alone before its own margin is counted. This is the logic of the multi-attachment fleet described in the clearing workflow.
Residual value and the cost of a poorly supported brand
Depreciation is the difference between what was paid and what the unit fetches at the end, so residual value is part of the ownership cost, not an afterthought. Attachments from brands with an Australian distributor, local parts and a recognised model line hold value better than unsupported imports, and a used buyer will pay for service records, a known serial and a build specification that can be confirmed with the factory (see inspecting used forestry attachments). A cheaper attachment with no parts pathway can cost more over four years once its resale value and its downtime are counted.
What the model tells you to record
A cost model is only as good as the hours and units fed into it, so the operating records matter as much as the invoices. For each attachment, keep productive hours, units produced, fuel per hour, wear parts fitted with dates and hours, and downtime with its cause. After a year, the real cost per unit for each attachment in the fleet is known, the tender rates can be checked against it, and the next purchase can be made on evidence.
Build the model before you buy
- Delivered price in the ordered configuration, including bracket, hoses, installation and freight
- Finance cost, insurance treatment and an honest residual value at the planned disposal date
- Wear-part prices and expected life in hours for every consumable, from local experience where possible
- Carrier cost per hour for this duty, including fuel, undercarriage, oil, cooling and operator
- Expected annual productive hours, with the work that will supply them named
- Expected units per productive hour, measured in representative Australian material
- Transport cost per mobilisation and expected number of mobilisations a year
- The alternative method's cost per unit, so the attachment has something to beat
Frequently asked questions
Why cost the carrier when I already own it?
Because the carrier's fuel, wear and operator are consumed by the attachment's hours, and they are far larger than the attachment's own costs. Leaving them out makes every attachment look cheap and hides the fact that the attachment has to earn the carrier's hourly rate as well as its own.
What utilisation makes an attachment worth buying?
There is no universal figure. Build the model with your own fixed costs and hours, then compare the cost per unit with hiring or subcontracting the same work. The break-even point moves with purchase price, finance cost and the carrier rate, which is why an illustrative threshold on someone else's numbers is not a substitute for your own.
How do I estimate wear-part life in Australian hardwood?
Ask the supplier for experience in similar species, run a paid trial and record consumption, and treat European softwood figures as an upper bound. Rock contact and dry abrasive soil shorten life further on stump and ground tools.
Does a rotator change the ownership cost?
It adds purchase price, weight and a service item, and it can save seconds on every cycle. In high-cycle handling those seconds add up to hours over a year, so the question is whether the cycles are frequent enough to pay for it.
Should residual value be included in the hourly cost?
Yes. Depreciation is purchase price minus residual value spread over the ownership period. A well-supported brand that resells strongly has a lower true hourly cost than a cheaper unit that is worth little at the end.
Get a recommendation, not just a price
Send us your excavator model, hydraulic figures, tree species and typical diameters. We will come back with a carrier-matched configuration and a written specification you can compare against any other quote.