Straight Edge

As shown in Fig. 66a, the under surface of the front iron must be perfectly flat so that it can bed evenly on the cut iron ; but if this face is found to be slightly curved, as in Fig. 66b, it must be corrected on an emery bench stone in the manner illustrated in Fig. 67. The iron should be moved on a circular path on the stone and with the side of the stone towards the operator ; this will enable the position of the blade to be clearly seen and accurately controlled. If the blade is merely pushed backwards and

forwards along the stone the edge will almost certainly be made rounded.

If the contact face of the front iron is not made truly fiat to bed evenly on the cut iron, the wood shavings will wedge themselves between the two irons and will then tend to block the throat of the plane.

Should, however, the curvature of the front iron be found to be excessive and too great for correction on the stone, this must be corrected by grinding on the side of the emery wheel.

Needless to say, the upper surface of the cut iron in both the single and double types of blade must also be perfectly flat, but it is hardly possible that a defect in this particular will be found in a tool of reputable make where correct methods /if manufacture are employed ; likewise, the cutting edge will be found to lie truly at right angles to the sides of the blade, and the proper angle to suit the work for which the plane is intended will be ground on the cutting edge.

Stoning the Gutting Iron. As has already been mentioned, the cutting angle of the blade of the block plane is usually 30 deg,, but where a double iron is used, as in smoothing and jack planes, this angle is reduced in value to between 20 and 25 deg., and the form of the ground blade becomes as depicted in Fig. 68. During

facet

facet

the stoning operation, however, this angle is made more obtuse by some 3 deg. or more, as in Fig. 69 ; this is in order to lessen the amount of work required during the final sharpening on the stone.

To ensure that this angle is accurately maintained right across the edge, a simple stoning jig of the type illustrated in Fig. 7, Chapter II should be employed.

This particular jig was brought to the writers' notice many years ago by a skilled cabinetmaker, who with the aid of this appliance sharpened his plane irons with truly remarkable speed and precision.

As will be seen in the drawing, this device comprises a frame and a clamp to hold and position the blade, and at the extremities of the side-members a hard wood roller is fitted which rolls on the surface of the stone.

The method of setting and adjusting the blade in the jig is also described and illustrated in Chapter II.

Alternatively, the blade can be set on a stone with a dry surface by adjusting the iron until the trailing part of the cutting edge is just clear of the stone's surface, as represented diagrammatically in Fig. 70.

When the blade has been set in the jig, it is moved backwards and forwards along the stone, which at the

ANCLE Ml EXAGERAT TO SHOW

ANCLE Ml EXAGERAT TO SHOW

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outset may be a fine grade of carborundum or India stone to give more rapid cutting. To begin with, firm pressure should be applied, but as the work nears completion the pressure should be reduced.

After a few passes have been made, the cutting edge should be examined to see if a wire edge has been formed, as indicated in Fig. 71 ; this can be felt with the finger

WIRE r EDGE

on the back of the blade, or it can readily be seen with the aid of a magnifying glass.

To remove the wire edge, the blade, while still held in the jig, is applied to the stone in the manner described for truing the front iron and as shown in Fig. 72 ; but it

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