“I’d like to put a saw on my machine for cutting trees or logs”

This is how many conversations start when someone is seeking to reduce the risk or effort involved in conventional tree care or chainsaw operations.

Seems straightforward (find a saw + fit it to machine), though there are a range of factors to consider when choosing an attachment to ensure safety for your operator, your crew on site and the public.

Different types of saw attachments

First, let’s take a look at some of the different forms of attachments using mechanised saw systems that can be used on an excavator or other type of mobile carrier.

 

Saw cassettes

A hydraulic chainsaw unit enclosed in a frame, for mounting to the side of a conventional log loading or sorting grapple with either fixed mounting to the machine, dangle or fixed type rotator or under a tilt-rotator. Designed primarily for ground-work such as cutting forked or over-length stems before loading or further processing. Purchased separately, or offered as part of a package assembled by the manufacturer or equipment dealer.

Felling grapples

Compact, purpose-built grapple attachment with built-in saw unit, rotator and tilting grapple frame, often weighing under 600kg. Highly manoeuvrable, and can “double-cut”, approaching larger trunk cuts from various angles. Designed for safely removing smaller sections from the tree, also very efficient feeding a chipper. Can be fitted to different carriers including excavators from 5 ton upwards, plus long reach combinations on truck cranes and telehandlers.

Fixed grapple saws

Heavy duty grapple type attachments with a fixed wrist type turntable rotator attachment to the excavator. Specifically designed for tree felling and limb removal works (and all tasks in-between). Strong turning or holding force in the rotator for handling larger tree sections or even whole trees. Generally suited to excavators from 14 to 30 ton with greater stability and hydraulic capacity. Not to be confused with a grapple and saw cassette bolted on.

Forestry felling heads

The inspiration for all smaller tree cutting attachments working outside forest areas. Large (2-3 ton) attachments  for felling and harvesting whole trees on forestry-specific carriers or converted excavators in the 25-35 ton class. Both ‘floppy’ and fixed type attachment to the machine. Feller bunchers for example are occasionally brought in as the “big guns” for storm or bushfire clean-up operations and utility clearing, though usually only seen on a logging site.

What’s the difference between a mechanised saw attachment and regular chainsaw?

A “Harvester” saw chain based cutting system is comprised of similar components to a chainsaw; a drive sprocket, guide bar, and a loop of saw chain, though is not hand-held, and designed only to work with mechanical harvester machines, including some of the types illustrated above.

The saw motor is driven by hydraulics from the host machine, as is the feed out cylinder which pushes the guide bar into the cut. High horsepower input and saw chain speeds are possible with a mechanised saw, and caution should be exercised to ensure manufacturer’s recommendations are not exceeded, and chain shot risks reduced.

Hultdins SuperCut – one of the most advanced and widely used hydraulic saw units in the world

What is “Chain shot” ?

A Chain Shot Event (CSE) occurs when a piece or pieces of cutting chain from the end of a broken saw chain in mechanised timber harvesting or processing is ejected at a high velocity. There is risk of serious injury or death to the machine operator, ground personnel and bystanders from chain shot.

Chain shot typically originates near the drive end of the cutting system but can also originate from the guide bar tip area. Saw chain pieces usually travel in the cutting plane of the guide bar, but can deviate to either side (see illustration).

Although the “Shot Cone Zone” reflects the most likely chain shot path, deflections can occur, substantially expanding where chain pieces may travel. To minimise risk, operators should keep out of the Shot Cone Zone, ground personnel and bystanders should be at least 70 metres away from cutting operations and out of the Shot Cone Zone.

How does chain shot happen ?

1. The saw chain breaks

2. After a saw chain break, the “free” end of the saw chain begins to whip away from the break.

3. If the saw chain is not contained by the saw box or a chain shot guard, the broken saw chain’s free end can speed up rapidly, carrying immense dynamic energy.

4. At the peak of the whip, saw chain pieces may break loose and be ejected at high speed.

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