[Fig. 6.] shews one of the Tines of a Drill-harrow made of Wood: Its Edge a b is made roundish at b, by which means it raises the Earth on its Sides; but does not drive it before: This Edge from a to b is Six Inches long; from b to c, being its Bottom, is One Inch and a quarter; from c to d is the Back, an Inch and an half thick at Top, gradually tapering downwards to c, where it is half an Inch thick, being shoulder’d all round: It has a flat Tenon A, which passes thro’ a Mortise in the Harrow-head; the Length of which Mortise is parallel with the Length of the Harrow-head, into which it is held by a Pin, passing thro’ the Hole of the Tenon, above the Harrow; as may be seen in [Fig. 7.] at a; and its Fellow at b.
These Two Tines are Eight Inches asunder at their Points, and Six Inches and a quarter asunder at their upper Parts, just under the Harrow-head. The fore Edge of the Tine A inclines a little to the Left, as the Edge of the Tine B doth to the Right.
[Fig. 8.] shews one of the Legs of the Harrow. At a is seen the round Tenon, which passes thro’ the Harrow-head up to its Shoulder, and is pinned in thro’ an Hole of the Tenon just behind the Harrow-head; upon this Tenon the Harrow-head may turn: The other End has an Hole at b, thro’ which it is pinned on to the Beam. The Length of the Leg from the Shoulder at a, to the Hole at b, is Twenty Inches: Its Thickness is an Inch and a quarter, and its Breadth an Inch. The Two Legs are seen mark’d C, D, in [Fig. 7.] They bend down in the Middle, to give the Harrow the more room for rising and sinking; they are parallel to each other, and distant a little more than the Breadth of the Beam, that they may have Liberty to move thereon, when one End of the Harrow-head sinks lower than the other, by the Unevenness of the Ground.
The Harrow is pinned on to the Beam by the Iron Pin, [Fig. 9.] passing thro’ the Hole of the Leg at g, and thro’ the Beam, and also thro’ the other Leg on the other Side of the Beam, where the Screw at the End of the Pin has a Nut screw’d on it. This Pin is round from its Head all the Way thro’ the first Harrow-leg, and thro’ the Beam; but all that Part of the Pin, which is in that Leg against which the Nut is screw’d, must be square; whereby that Part being bigger than the round Part of the Pin, and than the Hole in the last-mention’d Leg, cannot turn in the Hole of that Leg; for if it did, the Nut would be soon unscrew’d by the Motion of the Harrow; but the Pin must have room to turn in the other Leg, and in the Beam. This square Part of the Pin is seen at a, [Fig. 9.] The whole Length of the Pin, from its Head to the End of the square Part at a, where the Screw begins, is of the Thickness of the Two Legs, and of the Breadth of the Beam.
We sometimes set the Legs of the Harrow Two Inches wider asunder, by making them each an Inch thicker at their fore Ends in their Inside, and reaching Five or Six Inches behind their Iron Pin: These thicker Parts, bearing against the Beam, keep the hinder Part of each Harrow-leg an Inch distant from the Sides of the Beam, whereby the Harrow-legs are Six Inches asunder, instead of Four, by means of these added Thicknesses.
When a Drill is taken up to be turn’d, the Person that does it, takes hold of the Harrow-head, and lifts it up: The Legs of the Harrow, bearing against the cross Piece, support the whole Weight of the Drill.
When the Harrow does not go deep enough, we tie a Stone upon the Middle of the Harrow-head, by a String that passes thro’ the Holes at h. All the Wood of this Plough and Harrow is Ash, except the Limbers.
