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HOW TO SHARPEN A HAND WEEDER
by Patrick Wilson


Introduction

Although weeding by hand is never glamorous, it can be safe and efficient with a properly sharpened tool. Hand weeders (also called swing blades, grass whips, and weed cutters) take lots of abuse and need frequent sharpening, because they inevitably hit rocks, wood, and dirt along with the weeds and woody vegetation they’re intended to cut. Fortunately, sharpening these tools is easy.

I describe below how to make a weeder safe, easy to handle, and unlikely to fall apart, and then show how to use either a file or a belt grinder to sharpen both the common serrated-blade and the heavier non-serrated-blade varieties of weeder.


Optimizing the Tool

So you won’t get cut by a sharp blade, and the blade won’t get damaged if it bumps against other tools, make a simple sheath out of fire hose (figure 1) and use it to protect the blade whenever it’s not in use.

If you wrap a bicycle inner tube around the top foot or so of handle (figure 2) and duct-tape it in place, the handle with be more comfortable and less tiring to hold, you’ll have more control over the tool, and you’ll be able to maintain a good grip even if the handle gets wet.

Because the original bolts that hold a serrated blade in place tend to work loose, they should be replaced with 1/4" x 3/4" stainless steel pan-head slotted machine screws with lock washers and nylon nuts (figure 3). These won’t loosen. (Non-serrated weeders have blades riveted in place and hence no bolts to replace.)


Figure 1

Figure 2

Figure 3

Sharpening the Blade
  Serrated
 

Reverse the blade so that its bevel faces away from the handle, i.e., up, when the tool is held handle-down in a vise. Use a 10-inch mill file to remove enough metal to take out any nicks and to restore the serrations along the full length of the blade (figure 4). Be sure to wear gloves, because a slip while filing in the direction of the blade would otherwise be disastrous. The serrations on this type of blade can be restored many times, because a serrated shape is built into the metal stock that forms the blade.

Although sharpening serrated blades isn’t an exact science, try not to deviate too far from the original bevel angle of 25°. Check the angle periodically with a small brass bevel gauge or an engineer’s protractor (figure 5).

A belt grinder makes quick work of serrated weeder blades. A 40-grit belt, grinding into the edge, will hog off worn metal yet leave the edge adequately keen for its intended purpose (figure 6). Restoring the serrations is much more important than achieving a finely honed edge anyway.

When you’re finished sharpening, flip the blade back so that its bevels face up, towards the handle. It’s worth doing a quick sharpening job after every 10 hours or so of use rather than wasting time with a dull, frustrating tool.

 

Figure 4

Figure 5

Figure 6
  Non-serrated
 

Because they rely on heft and sharpness rather than serrations to do the cutting, non-serrated blades require finer honing than do serrated ones. The riveted blade can’t easily be removed—and doesn’t need to be, because its main bevels already face away from the handle. (Non-serrated blades are designed for bevel-down use; serrated ones, for bevel-up use.)

With the weeder’s handle held in a vise and your hands protected by gloves, use a 10-inch mill file to remove any nicks and to create an even 25° bevel along the entire length of the blade (figure 7). Verify the angle with a bevel gauge or protractor.

Hone the edge freehand by working through successively finer grits of sharpening stone. (See my drawknife article for suggested grits and for instructions on flattening stones.) Use a black marker to mark the bevel (figure 8) each time you switch stones, so you can see exactly where metal is being removed and keep from rolling the edge by holding a stone at too blunt an angle. Put on the final polish with 0.5µ chromium oxide compound applied to a piece of wood and carefully rubbed along the (marked) bevel. If you can see or feel any wire edge, use a fine-grit stone—very lightly and at an angle of just a few degrees—to hone the back bevel just enough to remove the wire (figure 9).

As usual, a belt grinder speeds up the whole process. Grinding away from the edge (figure 10), start with a 40-grit belt to remove any nicks, work through successively finer belts to hone the edge, and finish on a polishing belt charged with 0.5µ chromium oxide compound. At each belt change, mark the bevel so you can monitor metal removal. (See my axe article for tips on honing and polishing with a belt grinder.) If any wire edge remains, lightly hone the back bevel, as above.

You’ll end up with a brightly polished 25° bevel and a razor-sharp edge. When backed up by the heft of the tool itself, such an edge will cut dense, woody vegetation as if it were light weeds.

 

Figure 7

Figure 8

Figure 9

Figure 10

Resources
Good sources of sharpening equipment include:
  • Lee Valley Tools (stones and hones, basic belt grinder, chromium oxide compound)
  • Woodcraft (stones and hones, chromium oxide compound)
  • Van Sant Enterprises (belt grinders, belt grinder attachments for bench grinders, sanding and polishing belts)