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HOW TO SHARPEN A DRAWKNIFE
by Patrick Wilson

When to Use

Trail crews use drawknives to strip bark from logs before building checkdams, steps, and waterbars. It’s important to remove all the bark to keep destructive insects from hiding under it and to shave off any punky, unsound wood to provide solid, long-lasting raw materials for trail construction. Drawknives are also perfect for smoothing bark before painting blazes. The sharper the tool, the more proficiently each task can be accomplished.


How to Use

Drawknives are designed to be used bevel-up. Gently pull the tool down and toward you, skewing it at 45° to its line of travel and using a slight sideways slicing motion (figure 1). Be extremely careful not to pull the knife into your leg or other valuable body part. A properly sharpened drawknife will glide through wood with little pressure.

Skewing the blade of a drawknife, as with a chisel, lowers the effective bevel angle without decreasing edge durability, because the cutting force is spread out over a greater blade width. Geometry works to your advantage, in effect making the edge simultaneously strong and keen. (A 30° bevel skewed at 45° gives an effective bevel angle of less than 21°, but with the full strength of the 30° bevel.)


FIGURE 1

Design of the Tool

Drawknives, whether designed for carving, carpentry, or bark-peeling (our focus), are single-bevel tools with bevel angles of 25°–33°. They are essentially wide, short chisels. As with all edge tools, their edge angle (= bevel angle, for single-bevel tools) should be as small as possible while maintaining durability. About 30° is perfect for bark-peeling, although the exact angle isn’t critical, and many trail workers will simply want to follow the factory angle. You can check the bevel angle of your drawknife using a protractor or bevel gauge (figure 2).

FIGURE 2

How to Sharpen

Properly sharpening a drawknife involves techniques used for flat-backed, single-bevel tools like chisels and plane irons, as well as those for double-bevel tools like kitchen knives. (Excellent jigs exist for kitchen knives but not drawknives). The goal is to have a flat, polished back meet a consistent, polished bevel to form a razor-sharp edge. The tools and techniques described below have numerous applications.

 

Lapping the Back

The first—and critical—step in sharpening single-bevel tools is to lap (i.e., flatten) the back.


Sandpaper Method

Tape sandpaper to a flat surface, such as a granite surface plate (figure 3) or piece of plate glass and lap the back of the tool by rubbing it side to side while holding down firmly. Periodically use a crepe block (figure 4) to keep the sandpaper from loading with grit. It helps to draw a grid on the back of the drawknife with a marker so you can see where metal is being removed (figure 5).
Work through successively finer grits of sandpaper, e.g.,
USA100x (141µ)*
USA220x (60µ)
USA320x (45µ)
USA400x (23µ)
USA600x (16µ)
*100-grit, U.S. standard, 141-micron grit size. Japanese water stones use a different standard, herein abbreviated JAP. Grit size in microns is given for consistent comparison.
If the back isn’t polished enough for you at this point, finish lapping with fine stones, as below.
 
FIGURE 3

FIGURE 4

FIGURE 5

 

Stone Method

In the unlikely event that the back of your drawknife is already fairly flat, or if you don’t have a flat surface available for the sandpaper method, you can use diamond hones or flattened oil or water stones.
(For comparison, a grade-A surface plate is flat to within 0.0001" over its entire surface; glass, to within 0.001" per inch; and diamond hones, to within 0.003" per inch.)

 

Diamond Hones

Using a few drops of water on each hone, lap the back of the drawknife by rubbing it side to side while holding down firmly. Work through successively finer grits, e.g.,
     

X-Coarse (60µ)
Coarse (45µ)
Fine (25µ)
X-Fine (9µ)

    Oil and Water Stones
     

Flattening/Deglazing
Don’t underestimate how fast stones wear or how easily they glaze over. Never use an oil or water stone, especially for lapping, before flattening and deglazing it.

     
  • Rub coarse stones against an extra-coarse diamond hone under running water (figure 6). A DMT XX-Coarse (120µ) hone is perfect for the job, takes seconds, and doesn’t wear out.
  • Alternatively, lap coarse stones on a piece of plate glass sprinkled with a little water and USA90x (160µ) silicon carbide powder.
  • Fine stones can be flattened against coarse ones that are known to be flat (figure 7). Do not mix oil and water stones.
      Using oil or water as appropriate on each hone, lap the back of the drawknife by rubbing it side to side while holding down firmly (figure 8). Work through successively finer grits, e.g.,
       

Washita oil stone (29µ)
Soft Arkansas oil stone (20µ)
Hard White Arkansas oil stone (14µ)
Hard Black Arkansas oil stone (9µ)

       

JAP800x water stone (16µ)
JAP4000x water stone (3µ)
JAP8000x water stone (1µ)

      The sandpaper method, followed by use of the two finest water stones, is ideal. A final polish can be put on the back with Tormek paste (3µ) and/or chromium oxide polishing compound (0.5µ) (figure 9).
 

FIGURE 6

FIGURE 7

FIGURE 8

FIGURE 9
  Sharpening the Bevel
  A flat, polished back provides the necessary foundation for a sharp, consistent bevel. Although no jig is made for holding a drawknife at a constant angle against a stone, (as one would do with a chisel), a knife jig can be used for this purpose. Alternatively, stones can be used freehand, with the drawknife clamped to the edge of a bench. With either method, it helps to blacken the bevel with a marker so you can see where metal is being removed (figure 10).
  Power tools should not be used on drawknives. Dry grinders will draw the temper from the metal; both wet and dry grinders will produce a hollow grind and a weak edge. The finest sharpening job can be done only by hand.
  If lots of metal needs to be removed, e.g., to repair a damaged knife or to change the bevel, use a file (figure 11) or a XX-Coarse diamond hone (figure 12) while the drawknife is clamped to the edge of a bench. Then proceed with one of the following methods.
 

FIGURE 10

FIGURE 11

FIGURE 12
    DMT Aligner Jig (figure 13)
    Using a DMT thick-blade holder, clamp the jig onto the drawknife at one end, set an appropriate angle, and begin honing at the location of the jig, starting with the coarsest hone (figure 14). (The jig can be adjusted for a bevel angle up to 30° for most drawknives.)
    Move the clamp one inch to the side and hone at that location (figure 15). It helps to mark the back of the knife to guide the location of the clamp (figure 16).
    After removing metal all the way to the edge and along the full length of the blade with the coarsest hone, repeat the process with each of the finer hones. During each step be sure to remove all the striations left by the previous hone.
    After the bevel has been honed smooth and flat with the X-Fine diamond, it can be polished with Tormek paste (3µ) and/or chromium oxide polishing compound (0.5µ) applied to a piece of wood cut to the same size and thickness as the diamond hones. Stroke away from the edge only.
    To form a 1° micro-bevel, use a DMT ceramic (7µ) hone, which is slightly thinner than the diamond hones. The micro-bevel can also be highly polished using Tormek paste (3µ) and/or chromium oxide polishing compound (0.5µ) applied to a piece of wood cut to the same size and thickness as the ceramic hone. Stroke away from the edge only.
    Just as with kitchen knives, for which it was designed, the DMT jig enables you to produce a perfectly flat, consistent, and highly polished bevel on a drawknife. Highly polished edges not only cut better but last longer than cruder edges.
   

FIGURE 13


FIGURE 14

FIGURE 15

FIGURE 16
    Freehand Stones

FIGURE 17

FIGURE 18
    Although the DMT jig can’t be beat for consistency and repeatability, it is possible to do a fine job on a drawknife bevel without a jig, using diamond hones, oil stones, or water stones.
    Clamp the drawknife to the edge of a bench and lightly rub the hone or stone side to side, lubricating it with oil or water as appropriate (figure 17). Concentrate on keeping the hone or stone consistently dead flat against the bevel. With care, you will be able to see and feel whether you are hitting the bevel exactly.
    Work through the same sequence of grits as with lapping and finish with Tormek paste (3µ) and/or chromium oxide polishing compound (0.5µ) applied to a piece of wood (figure 18).
    By closely watching exactly what is being polished, it is possible to polish an approximately 1° microbevel—in addition to the primary bevel—along the entire edge.
  Stropping

FIGURE 19

FIGURE 20

FIGURE 21
  The final step in sharpening a drawknife involves lightly stropping both sides of its edge on a strip of leather charged with chromium oxide polishing compound (0.5µ). Hold the back of the knife perfectly flat against the leather and very lightly pull the knife, away from its edge, along the leather (figure 19). Then hold the bevel against the leather and very lightly pull it, away from the edge, along the leather, taking care to maintain the exact bevel angle (figure 20).
  Testing
  Razor Edge Systems makes a handy, inexpensive edge tester that can be used to quantify sharpness and detect even the most microscopic imperfections in an edge (figure 21). A level-100 edge, which can be achieved using the above methods, equals that of a brand-new razor blade.
Resources
  Leonard Lee’s Complete Guide to Sharpening (Taunton, 1995; ISBN 1561581259) is the most useful, comprehensive guide to sharpening edge tools; it includes sections on metallurgy, abrasives, sharpening equipment, and technique.
Good sources of sharpening equipment include
 

Diamond Machining Technology (DMT)
Lee Valley Tools
Woodcraft