I would have to say that about 25% capacity of load chart would be the max IF a kb manufacturer even says plug it in. These things as well as the r&r technically violated our safety standards for crane use imo...although lifting/lowering cuts do also fall into the same topic...the piece does not remain in the same orientation once cut. That being said...two guys taking a tree down from the ground at even 500 pounds at a time sounds like easy work...
Grapple Saw on Kboom
- Thread starter limbcontrol
- Start date
Lumberjack
Branched out member
My point in mentioning the excavator at first was that the same grapple saws can be used on multiple carriers (knuckle boom, log loader, excavator, etc).
My point 5 posts ago was that knuckle booms are no where near as robust as an excavator.
Robustness could be looked at as the boom system's ultimate strength vs lifting capacity over time. Using a knuckle boom grapple saw to fell a "large" tree whole likely would be foolish, while it could be entirely practical with a weaker, yet more robust mini excavator.
By the same token, the wide range of knuckleboom capabilities; widely varying capacities based on the individual knuckle boom's configuration at the time of loading (radius, height, outrigger settings); and the infinite configurations of the individual cut loads (dimensions, species, densities, center of gravity movement from initial position to hanging position) make it impossible to have simple and efficient rules or guidelines like saying "Knuckle booms utilizing grapple saws shall not exceed 25% of load chart." That is a throw back to the 10% of breaking strength for working strength rule regarding ropes.
That's not entirely accurate, based on what I've seen of knucklebooms in tree work. At last year's crane workshop put on by Tree Stuff, Mike took a log and boomed out until the crane was at some high percentage of capacity as indicated on the remote. In that aspect, you could grab a 4klb piece off the ground (no dynamic load, I am not advocating cutting and catching a 4klb piece) and telescope it out. I understand that's not what you meant, but I am trying to illustrate that guidelines require an extreme amount of forethought since they are supposed to be protecting absolutes, or as close as possible.
One thing I hope to avoid is knee jerk reactions governing this potentially huge game changer. Personal responsibility needs to increase in society in general (personal belief). This radical change could be nipped in the bud before it gets off the ground because it's uncharted (get the pun?) territory.
I have no issue helping to guide people to the best of my ability. As Mark alluded and my reputation attests, I am not pushing false or misguiding information for personal gain. In general I find that offensive, given the level of effort I put into my customers. I'm not butt hurt, my skin is thicker than that. Just wanted to explain my view point. Feel free to call/text any time and I'm happy to listen and share for knowledge's sake. (662-251-8686). When it comes to local competitors and my working company (Rutherford Contracting) I'm not so giving as it gives me a keen edge against the competitors.
Hopefully I've made the point that there are no hard and fast rules to adjust a chart by. When I'm not replying to this thread on my iPhone (or you call), I'll expound more into the variables I've thoight of that affect every individual pick. If someone pushed a knuckleboom manufacturer in a corner demanding a load chart, my fear is the knee jerk reaction I menioned where they either say some ridiculous number (like 2.5% of the chart) or the more likely "Use of grapple saws or similar devices on our products is expressly prohibited" which would open up a huge can of worms with regards to legalities and insurance, which could cause major damage to this potential breakthrough for our industry. 50 years from now it's completely reasonable in my mind that accessible trees are removed via machines with operators using computer added processes to get the tree down with a high degree of reliability in a variety of conditions (removals in the rain/at night anyone?).
Hopefully this comes across as an ernest depiction of what I intended.
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limbcontrol
New member
So the only time you have seen a knuckle boom work was at a demo day? Have you operated one? NCCCO? Mike' s point was to demo max capacity. He was not using a grapple saw putting stresses on the boom that is was not designed for. Apples and oranges.
Reading back on the thread you seem to be giving advice on the use of the grapple saw on a kboom. Even offering recommendation on what to do and how to use one. Honestly, I believe it's all premature talk. Find it offensive if you will, but we as crane operators do not respond well to others recommending unsafe work practices! Do you know why Kbooms look like a bent fishing pole when loaded? They were designed to have pressure being placed on them in this manner only and that is what my remote control reads, pressure being placed straight down from the hook.
In crane work there ARE hard and fast rules and those that do not follow them or consider them loosely end up as a story in another section of this forum. No set rules in place? There has got to be set rules!!! A safety margin we must maintain, you don't just start small and try to figure it out progressively. You first know by instruction, learning the charts, then operate. The consequences are too extreme in crane work.
I am not trying to give you a hard time, I am really just begging to know more on the safe work practices of this new technology.
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limbcontrol
New member
Just got off the phone with Gerasemik. he takes picks at approximately 500lbs at any distance, even up close, though his crane is rated for much more. Pretty conservative which I think is a good idea. I am looking forward to going out to visit him soon.
classictruckman
Participating member
- Location
- Ottawa Valley, Ontario, Canada
No you should be picking 16-1800 lbs. A kboom manufacturer is not going to produce a chart for this type of work, it's up to the operator to reduce the chart just like in normal tree work or demo work for that matter, when you're picking something out of the air, you can't put it back if it's too heavy, so you should be sticking to around 50% of your chart until you get closer to the ground.
Lumberjack, does the mecanil have holding valves on the grapple cylinder? I'm surprised to hear that the gmt starts to open under too much load.
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allmark
Participating member
I doubt a manufacturer will create a load chart just for a single attachment.
Find a manufacturer that will in writing condone personnel being lifted in place other than the use of a man basket.
The R&R and these grapples function entirely differently in how they hold the weight. I am very interested in these and think it's graeat this thread was started.
If your capacity is 4000# you should not be picking that anyway. If you constantly pick at capacity you need a bigger crane.
I don't see lumberjack as pushing anything he was just replying to a thread started by someone else and put time and effort into videoing and posting a unit at work.
Find a manufacturer that will in writing condone personnel being lifted in place other than the use of a man basket.
The R&R and these grapples function entirely differently in how they hold the weight. I am very interested in these and think it's graeat this thread was started.
If your capacity is 4000# you should not be picking that anyway. If you constantly pick at capacity you need a bigger crane.
I don't see lumberjack as pushing anything he was just replying to a thread started by someone else and put time and effort into videoing and posting a unit at work.
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I'm starting to think that the loads that should be taken has more to do with the actual weight of the grapple unit rather than the capacity of the crane.
The torsional forces and shock loading has to do with the weight of the grapple heads mass being able to resist the mass and leverage effect by the piece being cut.
The torsional forces and shock loading has to do with the weight of the grapple heads mass being able to resist the mass and leverage effect by the piece being cut.
Lumberjack
Branched out member
Finally time on a full sized keyboard!
I am not a crane operator.
I have seen knuckle booms perform tree work on a few occasions, and have used a variety of stick cranes to perform tree work ranging from 15t to 175t with the most common being in the 100t or 120t crane. I started my tree service in ’03, hired a crane for the first time in ~’05, and the last time I used a crane was last May, producing $18.2k of work doing two jobs in a very long day. My biggest tree picks to date have been 25klbs (~55’ radius), 22klbs (~60’ radius), and 19klbs (don’t remember the radius), all with a 120ton crane which I have worked from a ~30’ radius out to ~145’. I understand there are differences between stick booms, and do not attest to know every difference. I do attest that both are levers and there is shared physics between them.
My analogy was a knuckle boom could use a grapple saw as a grapple to pick a log off the ground (not a “dyanamic load” as compared to catching a cut piece) and telescope it out to the limits of the chart without breaking any rules. I understood that is not what you intended and even said so, but in a technical sense, that would be a grapple saw holding a piece at the edge of the chart. My point was in that particular application, you wouldn’t need to increase the margin of safety in your chart, even though you were using a grapple saw to move wood. You would need to account for the weight of the grapple saw and use your traditional chart. In that application, the grapple saw is little more than a mechanical “sling.”
The reasons I can come up with as I am typing this for why a knuckle boom resembles a fishing pole (more so than a stick boom and way more than older cranes) are:
1: (Simplified) In a weightless cantilever beam loaded at the end (approximation of a crane), deflection equals load multiplied times length to the third power divided by three times the modulus of elasticity times the second moment of area.
(Simplified) At the supporting end of a constant cross section cantilever beam (cranes are an optimized cantilever beam with varying cross section), max stress at the support is weight times length divided by elastic section modulus.
High strength steel has the ~same modulus of elasticity as any other steel. The fact that it has a higher yield point means it can take more stress in general and at the extreme fibers and still be inside the steel’s design factor for that application. The lower the strength of the steel is, the greater the section modulus must be to withstand a given stress. Section modulus can be increased by adding to the boom’s dimensions or thickness. Knuckle booms from the top tier manufactures are highly engineered, some are even built from proprietary steel. Because they are at the edge of our current engineering, they can utilize optimized configurations to extract exacting amounts of performance from a given shape and strength of material. All this sums up to a steel that can take more stress/load and thus more strain (deflection/bowing/fishpoling). This is also why stick cranes of yesteryear deflect considerably less than modern stick cranes, huge advances in engineering and steel production result in the newer booms able to take more stress on a smaller section modulus.
2: The sections of a knuckle boom are designed as an optimized cantilever beam that collapses and can collectively can fold into a given area. For example. the Effer 655 6S+6S with the manual pull out has 12 areas where it telescopes. There are tolerances between every section and the section it telescopes from. While these tolerances are small, they do add up when you multiply them times twelve in this example.
3: The weight of the boom itself causes deflection as it is part of the total load experienced by the collective “boom.”
I am not a crane operator.
I have seen knuckle booms perform tree work on a few occasions, and have used a variety of stick cranes to perform tree work ranging from 15t to 175t with the most common being in the 100t or 120t crane. I started my tree service in ’03, hired a crane for the first time in ~’05, and the last time I used a crane was last May, producing $18.2k of work doing two jobs in a very long day. My biggest tree picks to date have been 25klbs (~55’ radius), 22klbs (~60’ radius), and 19klbs (don’t remember the radius), all with a 120ton crane which I have worked from a ~30’ radius out to ~145’. I understand there are differences between stick booms, and do not attest to know every difference. I do attest that both are levers and there is shared physics between them.
My analogy was a knuckle boom could use a grapple saw as a grapple to pick a log off the ground (not a “dyanamic load” as compared to catching a cut piece) and telescope it out to the limits of the chart without breaking any rules. I understood that is not what you intended and even said so, but in a technical sense, that would be a grapple saw holding a piece at the edge of the chart. My point was in that particular application, you wouldn’t need to increase the margin of safety in your chart, even though you were using a grapple saw to move wood. You would need to account for the weight of the grapple saw and use your traditional chart. In that application, the grapple saw is little more than a mechanical “sling.”
The reasons I can come up with as I am typing this for why a knuckle boom resembles a fishing pole (more so than a stick boom and way more than older cranes) are:
1: (Simplified) In a weightless cantilever beam loaded at the end (approximation of a crane), deflection equals load multiplied times length to the third power divided by three times the modulus of elasticity times the second moment of area.
(Simplified) At the supporting end of a constant cross section cantilever beam (cranes are an optimized cantilever beam with varying cross section), max stress at the support is weight times length divided by elastic section modulus.
High strength steel has the ~same modulus of elasticity as any other steel. The fact that it has a higher yield point means it can take more stress in general and at the extreme fibers and still be inside the steel’s design factor for that application. The lower the strength of the steel is, the greater the section modulus must be to withstand a given stress. Section modulus can be increased by adding to the boom’s dimensions or thickness. Knuckle booms from the top tier manufactures are highly engineered, some are even built from proprietary steel. Because they are at the edge of our current engineering, they can utilize optimized configurations to extract exacting amounts of performance from a given shape and strength of material. All this sums up to a steel that can take more stress/load and thus more strain (deflection/bowing/fishpoling). This is also why stick cranes of yesteryear deflect considerably less than modern stick cranes, huge advances in engineering and steel production result in the newer booms able to take more stress on a smaller section modulus.
2: The sections of a knuckle boom are designed as an optimized cantilever beam that collapses and can collectively can fold into a given area. For example. the Effer 655 6S+6S with the manual pull out has 12 areas where it telescopes. There are tolerances between every section and the section it telescopes from. While these tolerances are small, they do add up when you multiply them times twelve in this example.
3: The weight of the boom itself causes deflection as it is part of the total load experienced by the collective “boom.”
Lumberjack
Branched out member
They are designed to withstand side loads which are produced by accelerating a load from slewing, wind loads on the boom as well as the suspended load, as well as side loads produced from not being set perfectly level.
According to the knuckle boom dealer I have the most time with talking to, their knuckle booms can operate way out of level, but they recommend staying within 5* of level and keeping the tires in contact with the ground to help spread the load (vs cribbing a stick boom crane to ~1* of level). 5* out of level setup with the above mentioned 655 6S+6S, assuming additional 5* of lateral boom deflection, an produce a side load of 273lbs (98.5’ boom length and a 1575lb load).
From my understanding, load readouts on a knuckle boom are based on readings from transducers placed on the knuckle/boom/jib/extension cylinders. This makes sense given the max pressures on the cylinders are at max loading regardless of boom configuration. For example, it doesn’t matter if the knuckle cylinder is at 50% pressure if the jib cylinders are approaching 100% pressure, the crane is limited by the jib. As long as all the cylinders stay within their designed operating psi, the crane is in chart. Hopefully that makes some sense.
Cranes are made to pick up “static” loads, not loads that are moving as craneguy1 mentioned. “… the piece does not remain in the same orientation…” and that’s the only practical way to produce a chart for a human to practically understand while in the field.
In one axis, the loads of a grapple saw are the same as rigging down a tree. According to ANSI 1/2” Stable Braid has a working strength of ~1klbs for tree work. However that is not a practical hard and fast rule if you apply it to say that it can catch a 1klb piece rigging trees. A 1klb 3’x3’ block imparts far different loading than a 1klb limb peeling down against the rope which is far different from a 1klb top being caught with a negative block which is far different from a 1klb top being lifted by a positive block. Riggers understand various properties and make informed decisions on what is practical and safe. Knowing 1/2” Stable Braid is rated for 1klbs working strength is far different than understanding how to apply that knowledge to practical use.
In that regard, there are many variables that I can think of that affect how a knuckle boom will respond to a piece being cut. I’ll type up another response illuminating my thoughts on those variables. There are similarities between a knuckle boom’s boom and an excavator’s boom in those regards. The required margins of safety are vastly different, probably by an order of magnitude or more.
Lumberjack
Branched out member
James, I doubt the Mecanil grapples do, but I can check. The GMT opens because the grapple circuit has a work relief installed. In other applications that's a very good thing, like running the grapple saw on a 12t excavator (A 312CL with a blade showed the highest lifting capacity to be 19100lbs!). The work relief is a cartridge valve and depending on how the valve block is made (with the guidance of GMT), it may be possible that the cartridge could be replaced with a load holding valve, but that isn't ideal for your intended purpose.
In my talks with a knuckle boom dealer here in the US, they said they would require a load holding valve in the grapple and showed me an example of a traditional grapple/rotator, with the load holding valve being plumbed in up by the rotator with hoses going to the cylinder (or it might have been above the rotator, don't remember). The load check would need to be mounted on the base of the cylinder, directly to the port, to get the most secure method. Any failure/compromise between the base side of the cylinder and the load holding valve will cause the cylinder to collapse. If the load holding valve is in the valve block, there is still the hose from the valve block to the cylinder to consider. If it fails, the grapple fails. The salesman and I disagreed in this regard, but there wasn't a practical way to illustrate this on a trade show floor.
The GMT needs a bleed valve/small orifice vented to tank in the grapple open side of the circuit to give fluid a place to go for tilt down and if the grapple is over powered. This could complicate the load check installation, but it shouldn't be insurmountable. The load check would negate the work relief for the grapple, and it doesn't matter if the open circuit falls to zero psi with regards to the load check's functions (assuming it gets its signal from the open side of the circuit to allow fluid out of the cylinder).
- Location
- Home of the New Jersey Devils
Well you sorta have a grasp of things 
Lumberjack
Branched out member
I have plenty to learn, always, but I feel pretty good about my foundation.
classictruckman
Participating member
- Location
- Ottawa Valley, Ontario, Canada
All cranes including kbooms are required to have holding valves to prevent the load being dropped in the event of a hydraulic failure, I understand why it's a safety feature to open the grapple during an overload in most applications, but not on a crane.
Lumberjack
Branched out member
I understand, one way or another it can be handled.
The dealer I was talking to said the arrangement on their grapple was fine. Extrapolating from that, hoses between the load check and the cylinder are ok to them.
On some outriggers the load check is on the port, on others it's connected with a steel line. If I was designing it would be on the port.
I've seen outriggers with the load check on the port, or connected with a steel line. The steel line has been welded or connected with a threaded fitting. The steel line is plausibly more robust than rubber hose for sure. If the threaded fitting loosens, the outrigger will collapse.
I'm certainly not trying to fear monger, only illustrate that every system has a weakness and nothing in this life is for certain.
The dealer I was talking to said the arrangement on their grapple was fine. Extrapolating from that, hoses between the load check and the cylinder are ok to them.
On some outriggers the load check is on the port, on others it's connected with a steel line. If I was designing it would be on the port.
I've seen outriggers with the load check on the port, or connected with a steel line. The steel line has been welded or connected with a threaded fitting. The steel line is plausibly more robust than rubber hose for sure. If the threaded fitting loosens, the outrigger will collapse.
I'm certainly not trying to fear monger, only illustrate that every system has a weakness and nothing in this life is for certain.
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allmark
Participating member
All the load holding valves I have seen don't prevent failure of the cylinder if anything before the cylinder fails it prvents fluid from escaping the cylinder. Therefore they're not a safety for overloading the cylinder
On the effer cranes if the cylinders are over loaded they will slowly bleed and lower the boom on the lift cylinders.
On the effer cranes if the cylinders are over loaded they will slowly bleed and lower the boom on the lift cylinders.
Lumberjack
Branched out member
Correct, Mark. Load holding valves, like a double pilot check valve, lock the fluid between the valve and the cylinder. Double pilot check valves require pressure on the open side of the circuit to allow fluid out of the base end of the cylinder (and the opposite in the extend direction).
Work reliefs, like on the GMT, are there to protect the cylinder/machine if the pressure in the cylinder goes over a set pressure. The system relief prevents you from pushing a cylinder beyond system pressure, but after the work valve is closed, the fluid in the cylinder is locked between work valve and the cylinder. If the load increases on the cylinder, there's no protection for the circuit without a work relief, which is just a pressure relief between the valve and the cylinder.
Effer drifting down like that is work relief valving, but they must combine the functions of the work relief and the load check valve. Work reliefs can dramatically increase the amount of energy absorption (shock load) the boom can handle without failure. I would like to see a schematic of their valving. The load check could be a velocity fuse combined with a work relief, for example. Lots of ways to get to the same result.
Work reliefs, like on the GMT, are there to protect the cylinder/machine if the pressure in the cylinder goes over a set pressure. The system relief prevents you from pushing a cylinder beyond system pressure, but after the work valve is closed, the fluid in the cylinder is locked between work valve and the cylinder. If the load increases on the cylinder, there's no protection for the circuit without a work relief, which is just a pressure relief between the valve and the cylinder.
Effer drifting down like that is work relief valving, but they must combine the functions of the work relief and the load check valve. Work reliefs can dramatically increase the amount of energy absorption (shock load) the boom can handle without failure. I would like to see a schematic of their valving. The load check could be a velocity fuse combined with a work relief, for example. Lots of ways to get to the same result.
SJ_Treeguy
New member
- Location
- Deep Southern NJ
Your the man Lumberjack !! Thats like 4 hours of typing , you explained it very well Thanks for the schooling in hydraulics and metallurgy, that helps me understand kboom construction and operation better. And i thought i knew a lot after 15 years of kboom ownership, my grandpa was right " you can learn something new every day".
Lumberjack
Branched out member
Thanks; happy to help!
I'm sure you have far more practical knowledge from experience!
I'm sure you have far more practical knowledge from experience!
Lumberjack
Branched out member
It's not a crane, but here's my latest video of the GMT035 on my mini excavator. I used to think a crane was out of reach for my little town in the South East US... I'm thinking a grapple saw may end up justifying buying a kboom, especially after spending the last two days taking down trees in the crazy Mississippi heat/humidity. A 655 6S/6S hd and grapple saw could have done all the aerial cuts except two (~60' of fat trunk, dropped two logs then the trunk from the ground).
Merle Nelson
Been here much more than a while
- Location
- SF Bay Area, CA
Scarry productive.
