Introduction

Trail crews routinely use bypass loppers to cut back woody vegetation, saplings, and tree limbs, as well as to swamp around blowdowns and work sites. Loppers are easy to sharpen, even in the field, and cut like new with a little care. The techniques described below work for all sizes of bypass loppers and for hand pruners, which are recommended for clipping roots while doing treadwork. (Anvil-style loppers require different sharpening techniques.)

The objective in sharpening these single-bevel tools is to restore the bevel on the cutting blade without compromising the blade’s flat back, which keeps the two halves of the tool meeting perfectly like scissors.

Periodically use a rust-eraser or steel wool to remove any rust from your loppers and lightly oil them after each use.

Keychain diamond hones (figure 1) are perfect for field sharpening, not only because they are thin enough to fit between lopper blades but because they are light and compact, require no lubrication, create a negligible wire edge, don’t wear out, and fold to protect their working surfaces.

With the loppers held wide open, preferably by another person, lightly hone the beveled edge at its existing angle until all nicks are removed and the bevel is of consistent width and even curvature (figure 2). If the blade is badly damaged, use a coarse or extra-coarse hone first, then finish with a fine or extra-fine one.

Never touch the flat back of the blade with the hone and never tamper with the hook on the opposite handle. Sharpen only the beveled edge of the blade.

Because a nick in the blade can fold over in use and compromise the flat back, it’s worth carrying a keychain hone to remove any serious nicks as soon as you notice them.

Even if you keep your loppers nick-free and periodically hone them freehand, sooner or later they’ll need a precision sharpening job. A DMT Aligner jig (figure 3), which is designed for knives, can easily be pressed into service on loppers. The jig uses diamond hones and enables you to achieve a perfectly consistent, polished bevel along the entire edge of the blade

Take apart the loppers and clamp the blade-handle in a vise, with the flat back of the blade level and facing down (figure 4). Use an engineer’s protractor to measure the bevel angle at several points along the blade (figure 5). A typical angle is 30°.

The key to using the DMT jig with loppers is to position a guide loop (made from an eye screw) at the center of curvature of the blade and at the correct height for the desired bevel angle. (The DMT knife clamp is too long to work on loppers.) Check the center of curvature and bevel angle by measuring the distance from the eye screw to the edge of the blade at a minimum of three points along the blade (figure 6) and by measuring the bevel angle with an angle-finder, also at a minimum of three points (figure 7). The measurements should be equal, as should the angles. Don’t let the guide loop move during sharpening: a millimeter discrepancy in any dimension equals nearly a degree error in bevel angle.

Mark the bevel with a black marker (figure 8) so you’ll know you’re honing in exactly the right places. Starting with the black, extra-coarse (60µ) hone (figure 9), remove enough metal to take out even the smallest nicks, to produce a thin wire edge (which you can feel with your finger) along the entire underside of the blade, and to form a smooth and symmetrical profile. As recommended by DMT, first rub the hone back and forth perpendicular to the blade, then rub it lightly lengthwise along the blade.

Marking the bevel each time you switch hones, work through coarse (45µ), fine (25µ), and extra-fine (9µ) hones to remove the striations left by each previous hone. Rub each hone perpendicular to the blade first, then lightly lengthwise along it. With a jeweler’s loupe (figure 10), you can monitor your progress and make sure you’re not switching hones prematurely.

To put a mirror finish on the bevel and remove any trace of a wire edge, polish the bevel with Tormek paste (3µ) applied to a piece of wood cut to the same size as the diamond hones (figure 11). To avoid gouging the wood, polish away from the edge only. If you can feel any wire edge on the back of the blade, remove it by holding the Tormek-impregnated wood dead flat against the back of the blade and lightly pushing away from the edge (figure 12). Finish by polishing the bevel (always away from the edge) on a piece of wood charged with 0.5µ chromium oxide compound.

Razor Edge Systems makes an elegant, inexpensive edge tester, which you can use to ensure that your loppers have a glass-smooth, level-100 edge (figure 13).

Before reassembling the loppers, lightly grease the threads of the bolt and the contact area between the blade and the hook.

Although a belt grinder can’t reproduce the precision bevel attainable with a DMT jig, a grinder will remove nicks and yield a perfectly serviceable edge in no time. After marking the bevel, hold the blade at an appropriate angle and guide it freehand across the belt, always grinding away from the edge to keep from removing too much metal or damaging the flat back (figure 14).

Use a USA400x belt (400-grit, U.S. standard, 23µ grit size) to remove nicks, then switch to USA600x (16µ) and USA1200x (6µ) for final honing, marking the bevel at each belt change. Finish with a polishing belt charged with 0.5µ chromium oxide compound, always polishing away from the edge. Never grind or polish the flat back of the blade.

Test the edge and reassemble as above.