Fig. 10
DIAGRAM SHOWING DOUBLE SHEAR STROKE OF THE
KNIFE PASSING OBLIQUELY THROUGH THE PILE
At the beginning of the stroke the knife is higher at the right-hand
side; when finishing the cut the knife is parallel to the table
To ascertain if a knife has a correct face, hold it flat, face up, with one end on a window ledge, and look along the face for variations. This is a simple matter which any one can do. Use a perfectly straight and clean-edged steel rule and pass it along from one end to the other as shown in Figs. 11 and 12. A dark spot shows the point of contact of the rule with the knife. These dark spots should show only exactly at the cutting edge and at the back edge. If a dark spot shows away from the cutting edge, it indicates that the knife is imperfect there and will not make a true cut. Regrinding the face by the makers can correct this fault, except where it is the fault of the one who hones the knife after it is sharpened.
Fig. 11
Fig. 12
Hone the knife only on the bevel. To remove the wire edge burrs along the edge lay the hone flat on the face and rub gently so as not to round over the edge.
A knife will sometimes cut better after it has been ground the first time. A polished knife will give a better surface to the cut. The cutting of the same kind of stock will often vary with different makes of knives. An oily rag tied to a stick kept handy and passed along the bevel of the knife before cutting hard stock will improve the cut. A blunt bevel is preferred for hard stock; a long, thin bevel for soft stock.
A general rule for the length of bevel on knives is two and one-half times the thickness of the knife. This may be varied to suit the different materials to be cut, but must be held within reasonable limits to preserve the strength of the cutting edge of the knife and also to secure accurate, clean cutting.