Knuckleboom Best Practices, Part 2: Grapple Saws

This is the second part of a two-part series. Part 1, “Knuckleboom Crane Best Practices in Tree Care,” also by Ben Heller, ran in the February 2020 issue of TCI. Click here to read Part 1.

Over the past half a decade, grapple saws have proven themselves to be dependable and safe while working over houses and other obstacles
Over the past half a decade, grapple saws have proven themselves to be dependable and safe while working over houses and other obstacles. All photos courtesy of the author.

All knuckleboom-crane best practices apply to operating with a grapple saw, and there are some additional things to keep in mind when using a grapple saw. I would like to believe that this article will be a starting point or at least a reference for creating a safe, productive work site utilizing grapple saws, no matter what kind of boom they are attached to, be it a 160-
meter-ton crane or a 20-meter-ton crane, a 7,000-pound-capacity log loader or a 50-ton excavator, a material-handling articulated loader or a helicopter.

Walk-through of the job site

One should always start with a walk-through of the job site and sometimes the surrounding area before setting up the equipment. This is a great time to evaluate and plan the intended work process – where the equipment will be placed, what mitigations might be necessary for placing equipment, etc. Things to be thinking about are the landing zone, the pathway to the landing zone and the work area, both in the tree and in the landing zone.

Grip location can sometimes be challenging, but creativity helps meet the goal.
Grip location can sometimes be challenging, but creativity helps meet the goal.

It is good to examine the crown of the tree, carefully looking for deadwood, branches fused together, close-growing branches, cabling hardware, bolts and anything else that might need special attention, especially so because without having someone up in the tree, some defects, hazards or hardware might not be readily noticed. Obviously, utility wires, power lines, structures and yard accessories also will be duly noted and considerations given.

Piece-size selection

When using only the grapple saw to effect the work, the operator has sole responsibility for piece-size selection and exact cut placement, as well as controlling the branch or log as it is brought from the tree to the landing zone and released. Exact weights are mostly not known. We rely on how the cut-off piece moves, or does not move, to assess proper piece size, not necessarily piece weight.

One popular saw head has hydraulic-tilt cylinders that remain held in position unless a valve is opened by the operator. Alternately, when the torque applied by the length and weight of a branch is enough to cause the hydraulic pressure in the cylinder to become more than the relief, oil flows out of the cylinders and the saw head tilts down to the stops.

Another popular saw head has what is referred to as “sequential operation” of the functions, and the saw head normally tilts down after the cut has been made, when hydraulic pressure has gone down and flow has been stopped. This saw head also can be made to hold the tilt cylinders in place through control functions. In both types, the action of the branch after it has been cut gives a relative idea of weight by observing the movement – or non-movement – of the piece during the cut and after it is cut off.

The torque applied at the grapple hanger, with the torque value often derived more from length than actual weight,  affects the way a piece will move after it is cut off.
The torque applied at the grapple hanger, with the torque value often derived more from length than actual weight, affects the way a piece will move after it is cut off.

Another thing to note is that, when using the grapple saw to make the cut, piece size is more dependent on the desired outcome of the action it will make or not make when it is cut off, as well as the landing-zone space available – not always the capacity of the crane in a given position or the load radius. There are other grapple saws available that may use these same types of functions, and there also has been a development of a system that effectively blocks any tilting action of the saw head itself, as well as the link connecting it to the boom.

Any saw head that is designed to hold a branch, or whole treetop, without tilting will have its own set of operational parameters. I don’t think they should be excluded from these thoughts, but also remember that they operate differently and will have their own unique characteristics.

Saw-head maintenance

Thorough and regular inspections and maintenance are just as important for the grapple-saw head as for the crane or any other piece of critical equipment. Inspect the hanger, rotator and pins to see that nothing is missing. Check for cracks or damage to the structural components. Look for any hydraulic leaks or badly chafing or damaged hydraulic hoses. Replacing a hose at the shop that you suspect is close to failure will save valuable time on the job site, not to mention provide peace of mind. It is also invaluable to carry a supply of spare hydraulic hoses, steel plugs and caps and any other parts specific to your applications so that, in the event of an on-the-job failure, you can be back up and running in a short time. A separate toolbox on the truck is a great place to store these things so they stay clean.

Mounting the saw head

A safety lynch pin with stiff wire added in such a way that the spring clip cannot be opened by a stray branch.
A safety lynch pin with stiff wire added in such a way that the spring clip cannot be opened by a stray branch.

Most knuckleboom-crane configurations utilize a manual boom extension pulled out only partway (and some all the way) and pinned in place. This is to keep the hydraulic booms and parts out of the tree branches. The saw head is then pinned onto the manual extension and hydraulics are connected by means of a multi-connector that connects all four hydraulic lines with a simple lever action and lock button.

For normal use, the pin for the manual extension is typically secured with a spring-loaded clip, but this can be interfered with by a tree branch. I actually lost one completely and did not realize it until I was taking off the saw head. So a means of securing the clip, such as the use of a cotter pin, is a good idea.

This cotter pin almost came out of the nut and pin for the sawhead.
This cotter pin almost came out of the nut and pin for the sawhead.

The pin securing the saw head should have a nut that threads onto it and then a cotter pin through the pin that secures the nut from turning off. The cotter pin also should be monitored in case of tree branches disturbing it.

It is imperative to remember that the manual extension the saw head is hung from is limited in weight capacity to its rating. Know what that rating is and plan accordingly. Grossly exceeding the rating will result in damage to, or failure of, the extension. The saw head can be pinned directly onto the hydraulic extensions for heavier loads, but do not exceed the saw-head manufacturer’s rating. A bent or otherwise damaged manual extension should be removed from service immediately.

Manual extensions are not rated for the same capacity as the fly jib or hydraulic extension they are inserted into. For example, my manual extension is rated for about 1,200 pounds fully extended, but maximum capacity of my fly jib is 5,100 pounds fully retracted, horizontal and with the main (outer) boom in a position that also can support that capacity.

Be careful not to take on a bigger piece than your equipment can handle safely.
Be careful not to take on a bigger piece than your equipment can handle safely.

The hydraulic cylinder for the grapple must have a load-holding valve for the side of the cylinder that closes the grapple. No leaks may be present from the cylinder, fittings, the steel lines between the holding valve and cylinder or the holding valve. The holding valve is required for two reasons – in case of complete failure of hydraulic hoses anywhere in the system, and because many knuckleboom cranes and other equipment are using what is called an open-center, hydraulic-valve system. This means the valves are not relied on to hold oil pressure to any function/hydraulic actuator, i.e., a cylinder, motor, rotator or anything that hydraulic pressure and flow are used for to make movement. In fact, the oil pressure in the lines to a function essentially goes to zero once the control valve is released.

Carrying spare hoses and other parts can be invaluable in case of a problem in the field.
Carrying spare hoses and other parts can be invaluable in case of a problem in the field.

Saw chain

The saw chain should be tensioned correctly and sharp. Dull chain, uneven sharpening and a bent or damaged guide bar will cause binding in the cut. Dull chain will cut slower or sometimes not at all if extremely dull. Be sure the oiler mechanism is functioning properly and is adequately supplied with good-quality bar-and-chain lubricating oil.

Maintenance and inspection go together to promote safe and  successful work.
Maintenance and inspection go together to promote safe and successful work.

Once the saw head is attached and ready, it is good to make a quick function check before going for the first cut. This is a good time to observe the saw-chain tension and oiler function. Correct chain tension is much like a handheld chain saw – tight enough that it can be just pulled away from the guide bar. Other things to look at are excess wear or damage to the bar and a bent bar or bar mount, as well as any obviously loose or missing hardware.

Some grapple saws use an onboard, 12-volt battery to power a radio receiver and the electric solenoids that actuate the valves. The battery charge lasts quite a while, and if changed regularly, depending on use, it will be less likely to go dead in the middle of a cut. You also can disconnect the battery at the end of each workday, which will drastically prolong battery-charge life.

Acquiring the target

Target acquisition can be a little bit complicated, but taking a nice, easy-sized branch first is a good idea. What we need to remember is that, when using a grapple saw, the weight of the cut pieces is usually similar for most pieces, but the dynamics can be quite different. The dynamics of the cut branch are more important to consider than the actual weight of the branch. In this sense, we are not basing piece size and weight on how much the crane can lift in a given location, but rather on what the branch will do as and after it is cut off. When determining where to place the saw head for the cut, many things need to be considered.

Take into account the movement and tipping down of large branches. Smaller or dead branches may break off and fall, or perhaps it is not acceptable to have the branch end tip down at all because of an obstacle. In that case, taking a smaller piece is necessary.

When choosing where to grip and cut off a branch, make certain an adjacent branch is not in the path of the saw. It can be a bit surprising to see another branch fall from the tree before the target branch is cut through. In addition, beware of breaking off branches unintentionally when closing the grapple. An extra branch included in the grip can break suddenly, causing the grapple to close rapidly, which may cause the top part of the broken branch to break off and fall. Dead branches are more prone to this. The grip of the grapple is extremely strong and will break branches even four inches in diameter.

In addition, if the grapple saw is positioned where a lump or small branch is in just the wrong spot, it can interfere with the travel of the bar or the bar mount, which prevents the cut from being fully made.

In the spring/early summer, when the bark can be sloughed off, one should be extra careful with how the branches are formed and where the cuts are made. Even though, and maybe because, the grip strength is so great, the bark can slip loose and a branch can rotate within the grapple, sometimes causing it to come partway out of the grip. This happens in particular with “dogleg”-shaped branches or branches that are unevenly weighted from one side to the other. As you can imagine, this can be a bit exciting when positioned over something important that needs to be protected from damage.

Landing zone

It should be communicated in the job briefing that, when bringing cut sections to the landing zone, all personnel should stand clear until the grapple saw is clear from the immediate area. There are cases when an odd or awkward piece needs to have one or more cuts made with a handheld chain saw or power pole saw before the grapple saw can relinquish its grip. This requires special caution and clear communication on the part of the operator and the cutter.

Taking wood sections greater than 12 inches in diameter becomes a little different because there is much more mass involved and the sections must be shorter to prevent shock loading the crane boom. Too large (too long) a piece will cause the saw head to tip down forcefully, shocking the grapple saw and the crane.

Securing a pick

While there may be conflicting opinions about doing it, the grapple saw with tilt function can be used as a means of securing a tree section while an arborist aloft cuts the secured section farther down, below the mechanical rigging connecting the tree section to the boom. I believe this should be an acceptable practice, as long as there is a functioning load-holding valve preventing the grapple from opening without hydraulic oil being supplied to it under pressure.

Larger-diameter wood sections can be successfully removed by making two or three cuts and being certain of grip.
Larger-diameter wood sections can be successfully removed by making two or three cuts and being certain of grip.

Conclusion

There are many aspects to operating a knuckleboom crane and even more when a grapple saw is added to the mix. Approaching the work step by step and taking the time to train, maintain and plan, followed by executing the work and being ready to adjust the plan, will pay off in increased production with fewer man hours expended.

A very special thank you to Alex Gulledge and Rick Yoos for their help and contributions to this article, along with the many others I spoke with about grapple-saw use, and to the staff at TCI Magazine for the invitation to write this article.

Benjamin P. Heller is owner and chief operations officer with Hiawatha Tree Services, an 11-year TCIA member company based in Minneapolis, Minnesota.

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