Thumbs and grapples allow an excavator to pick, place and sort demolition materials with relative ease. But selecting the appropriate tool for your job is complicated by the wide assortment of options. There are many different types and configurations of thumbs and grapples, each offering unique benefits and limitations.
Make the right choice and you will be rewarded with increased productivity. Choose the wrong attachment and productivity will suffer and/or attachment uptime and overall life will decrease.
Bucket Thumb Considerations
The bucket/thumb combination can handle most tasks, and if you need to dig with your machine, it provides an effective solution. Like the thumb on your hand, the excavator bucket thumb can grasp oddly shaped items, then folds out of the way for normal digging and loading.
Yet, this is not a one-size-fits-all solution. “There are a lot of thumb styles on the market today,” says Tracy Black, operations manager, Kenco. “Most thumbs are designed to handle just about anything, but certain types can be more productive.
“For example, if the debris is smaller in nature, then a thumb with four tines spaced closer together would be much better than two tines spaced further apart,” he explains. “Larger debris allows for less tines and greater spacing, which in turn gives the operator better visibility. The thumb will also be lighter, which gives the machine a larger payload.”
Also available are both hydraulic and mechanical versions with a variety of teeth that intermesh with the bucket teeth. Mechanical thumbs are typically mounted with a simple weld-on bracket with no special pins or hydraulics required. They provide a low-cost solution for occasional use, while hydraulic thumbs provide a strong, positive grip on the load.
“Having the added flexibility and precision of a hydraulic thumb will prove more efficient over time by allowing the operator to easily grasp objects,” says Mark Nye, Nye Mfg.
There is a trade-off between cost and productivity, however. “Hydraulic thumbs are more expensive but they will outperform a mechanical model,” notes Black. “Most purchases are relevant to the amount of work done with the thumb. If you use it every day, I recommend going hydraulic. If it’s an occasional use, mechanical might make more sense.
“Mechanical thumbs are fixed in one position and the bucket must curl against it,” he points out. “Most mechanical thumbs have three manually adjusted positions. A hydraulic thumb has a greater range of motion and allows the operator to control it from the cab.”
Some manufacturers also offer progressive link hydraulic thumbs, which provide greater range of motion, often up to 180°. This allows the thumb to grip throughout the entire range of the bucket. You can pick and place objects further around the end of the stick. It also provides load control through most of the bucket’s range of motion. By contrast, no-link hydraulic thumbs are simpler and lightweight with a range of motion typically from 120° to 130°.
Thumb mounting styles also affect performance. Universal-style thumbs, or pad mount thumbs, have their own main pin. A baseplate welds to the stick. A pin-on style thumb uses the bucket pin. It requires a small bracket to be welded to the stick. A hydraulic pin-on thumb is able to maintain its relationship with the rotation of the bucket and is engineered to match the bucket tip radius and width.
“Thumbs that hinge with the bucket pin allow the thumb to rotate on the same plane as the bucket,” says Black. “Thumbs hinging on a stick-mounted plate tend to shorten their relative length to the bucket tip radius when it’s rolled out. Pin-mounted thumbs are typically more expensive. Weld-on thumbs are more generic in nature and designed to work in their respective excavator weight class.”
Nye suggests there are several advantages to pin-mounted vs. stick-mounted thumbs. With the pin-mounted thumb, the tips intersect with teeth regardless of bucket position (full curl to partial dump). “When the bucket is removed, so is the thumb, which means it is not sticking out under the arm where it could possibly get damaged or be in the way,” he comments. There is no pivot bracket on the stick to interfere with other attachments.
Pin-mounted thumbs also work well with pin grabbers and quick couplers. “The thumb stays with the machine independent of the bucket,” says Nye. But with no quick coupler, the main pin and thumb has to be removed with the bucket, meaning extra work.
There are also several advantages to stick-mounted thumbs. “The thumb stays with the machine and is unaffected by attachment changes,” says Nye. It is easy to remove when not needed (except baseplate and pivots). But the tips will only intersect the bucket teeth at one point, so thumb length is important. “When using a pin grabber, the thumb needs to be extra long, which increases twisting forces on the bracket.”
When selecting a thumb, it’s important to match the bucket tip radius and tooth spacing. Width is also a consideration.
“Wider thumbs are good for picking up bulky materials like municipal waste, brush, etc.,” says Nye. “Yet, wider thumbs produce more twisting force on the bracket, and more teeth equal less clamping force per tooth.”
“A wider thumb will offer more material retention, especially if the bucket is also wide,” says Black. “Again, debris size can be a factor along with the loading protocol. If the bucket is primarily carrying the load, the thumb is being used in a supportive role. If the machine is using the bucket in the neutral or rolled-out position, the thumb is now carrying more of the load so width becomes more of a factor.”
A grapple attachment will typically be much more productive in most applications (demolition, rock handling, scrap handling, land clearing, etc.) than a thumb and bucket. For demolition and serious material handling, it is the way to go.
Productivity will be much better with a grapple in applications where you are handling the same material over and over and don’t need to dig with the machine. It has the capability to grab more material in a pass than with the bucket/thumb combination.
Grapples also tend to work better on irregular objects. Some items grapples can lift easily are hard pressed to fit between a bucket and thumb combo.
The simplest configuration is the contractor’s grapple, which features a stationary jaw and an upper jaw that operates off the bucket cylinder. This type of grapple tends to cost less and there is less maintenance.
Demolition and sorting grapples can greatly enhance the productivity of primary or secondary demolition applications. They are capable of moving large volumes of material while sorting recyclables.
“In most situations, a demolition grapple would be the ideal choice,” says Black. “Demolition grapples provide great versatility by affording the operator the ability to not only pick debris, but also create it. Lighter grapples are available but aren’t typically recommended for demolition. Similar to thumbs, if the demolition is being created by another means, then a lighter duty, wide grapple might suit your needs better.”
Sorting and loading can be optimized using different types of grapples for each application. “Sorting requires customer input to determine what is to be picked while letting waste fall through,” says Black. “This grapple type allows the operator to rake the material as well as pick and load.
“Depending upon the material and whether or not the grapple is being used for any of the demolition will probably dictate what is used for loading,” he continues. “Most contractors are going to use what is on the machine to do everything. Given the opportunity, it would be ideal to have both on the job. The demolition grapple could handle the heavy work and let the lighter/wider grapple come in to take care of the smaller material.”
Durability is critical when handling demolition debris. “Most sorting grapples have internal cylinders and rotate motors which require two extra hydraulic circuits. They are not as strong and durable as mechanical demolition grapples,” says Nye. “Most loading is done with mechanical grapples where the operator can smash the material down for compaction without damaging the grapple.
“Mechanical demolition grapples are simple with virtually no moving parts,” he continues. “Maintenance costs are kept to a minimum and wear parts are limited to abrasion from loading/unloading materials. A good operator can spin, flip, manipulate and sort materials fast and effectively with a mechanical grapple with no need for the expense and headache of a rotating sorting grapple.”
If the application demands precise material handling, however, a rotating grapple may be the better choice. It offers up to 360° rotation, which allows the operator to grab from any angle without moving the machine.
In the right job situation, a rotating grapple can outperform any fixed grapple. The downside is that with hydraulics and rotators, the price goes up. Weigh the initial cost vs. the expected gain, and be sure to check the rotator design to make sure it is fully protected from debris.
Tine spacing is an important consideration for material to be sorted. “Ideally, the unwanted material should easily pass through the grapple,” says Black. “This creates quicker, more productive cycle times.”
There are many different tine configurations available. Typically, if a customer is working with smaller debris, a larger number of tines is the way to go. Demolition grapples usually have a two-over-three tine configuration for picking larger items. Brush or debris grapples are normally a three-over-four tine design. The more contact area the grapple applies to the load, the more the clamping force will decrease.
The type of material being handled will have a major impact on the most appropriate tine configuration. “Heavy steel beams and blocks call for a two-over-three tine configuration,” notes Nye. “General-purpose demolition calls for a three-over-four tine configuration. Brush, municipal waste and bulky materials call for four-over-five tines. Precision picking calls for an optional hydraulic brace rather than a standard rigid brace.”
Seek advice on tine spacing based on the material you handle. “Kenco has provided grapples for all types of material,” says Black. “We have the ability to create custom tine spacings which allow certain size debris to fall through while retaining what is needed. These tine spacings can also be plated off to retain as much as possible.”
There are also plate shell and rib shell designs available. Plate shells are used more in the waste industries vs. the rib shell version, which tends to get material stuck within the ribs. The plate shell stays clean and keeps working longer. However, the depth of the ribs on the ribbed version gives strength to the shells. The ribbed design also allows for increased visibility and screening of material.
Quick Couplers Impact Choice
Certain demolition grapples can work with or without a quick coupler. (Direct pin-on grapples typically do not work well on couplers.) If you intend to use a quick coupler in the future, it’s best to purchase it with the grapple, since grapples should be set up at the factory to work with the coupler. It is quite expensive to retrofit grapples at a later date.
“Quick coupler-mounted grapples are a compromise,” says Nye. “They may tend to ‘double act,’ making it a little more challenging for the operator to master. Forces are lower due to the pin centers and extra height. Direct pin-on grapples offer the most simple and effective option for mounting. There is no double action and the machine’s breakout force is increased due to increased pin center distance.”
Purpose-designed coupler-mounted grapples are available. “Kenco offers a coupler-mounted grapple that keeps the same geometry as a pin-on version,” says Black. “The two halves of this grapple are connected via two short pins, which are kept in direct line of the machine stick pin. This gives you the proper rotation without sacrificing coupler usage.”