​The Cutting Dynamics of the Hickok Pruning Lopper

tree-lopper-26-aluminum.jpgThe Hickok Pruning Lopper, also called a tree shear, is a deceptively simple piece of equipment, its design masking thousands of hours of laboratory and field testing necessary to bring it into production. All that simplicity is based on some very sophisticated principles of cutting dynamics.

The Lopper as Lever

First, start with the principle of the lever, one of man’s oldest tools. The lopper—or scissor-type lever—is a Class I lever with its fulcrum or pivot point (the centerbolt) between the weight and the effort. If you are prying a boulder out of the ground you are using a Class I lever: the boulder is the weight, the effort is you pushing down on the bar and between you and the weight is something to pry against—the fulcrum. Your Hickok Lopper is the same: the weight is the branch between the blade and the hook, the effort is your arms pushing the handles together and the fulcrum is the centerbolt.

As you recall from high school physics, the greater the distance between the fulcrum and the effort, and the shorter the distance between the fulcrum and the weight the less the effort required. In lopper design, then, the placement of the centerbolt in relation to the cutting area of the blade and hook is a critical element in the “cutting geometry” of the shear. Rest assured that your Hickok Pruning Lopper employs some of the most sophisticated cutting geometry ever devised.

Bypass vs. Anvil

Your Hickok Lopper is a “bypass” type shear. The blade “passes by” the anvil or hook. Compare this action to an anvil-type pruner where the blade comes in direct contact with its opposing element, the anvil. The anvil supports the branch while the blade crushes its way through the tissue. Anvil type loppers are useful for cutting old, dead wood and a limited number of pruning cuts but the blade soon dulls and the cuts are not the clean, diagonal cuts preferred by professional pruners. 

Your Hickok bypass pruner, with its proper geometric design, cuts with a sophisticated slicing action using the hook as a finger to hold the branch just right for the clean, slightly angled cuts that allow the branch to heal quickly. In a properly designed, well-maintained and properly used tool the blade never contacts the hook, thus remaining sharp and efficient for thousands of cuts. 

The Cutting Dynamic

As the blade cuts through the branch, the hook supports the branch, holding it in position for the blade to do its work. The forces on the blade change as the blade slices through the tissue of the branch. Picture the side loads as the angled blade cuts into the tissue. The material being cut tries to push the blade toward the hook. The blade must be strong enough to resist this side force, otherwise the resultant steel-on–steel contact will soon dull the blade. If the blade is ground very thin to be sharp, the resistance of the wood is enough to roll up a flimsy blade to one side, making it nearly useless. 

The answer is to grind the blade just right—thin enough to cut efficiently but left strong enough to resist rolling. Helpful in this task is precise ”hollow grinding," removing a certain amount of material in the “hollow” behind the cutting edge of the blade to keep it thin but not enough to allow it to roll. 

Another helpful technique is grinding a slight bevel on the side of the blade next to the hook. This backside bevel (back bevel) helps counter the side force the branch exerts on the blade and insures that the blade edge will never come in direct contact with the hook — the bevel will always push the blade away from the hook. A slight bevel on the back side of the hook assists in this action. 

Careful maintenance (with a sharpening stone) of these various bevels near their factory sets will result in years of efficient cutting and long life from your Hickok Lopper’s blade, hook and other components. The bevels are extremely important in preventing misalignment of the blade and hook.

Keeping it Light

All this grinding, beveling and fine-tuning takes place in a very weight-sensitive environment. Your Hickok lopper head is one of the strongest yet lightest devices of its type ever made. If you consider that the lopper head functions at the end of handles more than two feet (60 cm) long the reasons for weight reduction become obvious. A long day holding a poorly balanced tool with a too-heavy head takes a toll on one’s forearms.

Your Hickok lopper’s balance point is much further aft on the handles than competitive brands. This means the Hickok head is lighter, the tool better balanced, and consequently, easier on your forearms.

Jan 29th 2015

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