Care should be taken to work back to the lines gradually, to cut only part way thru from each side (in the case of a thru mortise-and-tenon), and to keep the cut faces perpendicular to the surfaces.
In sharpening a chisel it is of first importance that the back be kept perfectly flat.

The bevel is first ground on the grindstone to an angle of about 20 deg.

and great care should be taken to keep the edge straight and at right angles to the sides of the blade.
[Illustration: Fig.77.Whetting a Plane-Bit.] After grinding it is necessary to whet the chisel and other edged tools.

(See also under oilstones, p.

121.) First see that there is plenty of oil on the stone.