Part 59

The Hole in the Spring must be somewhat bigger than the Holding-screw, because the Spring must have room to move and play thereon.

If the Middle of the Spring were against the Middle of that Part of the Tongue, that is betwixt its Axis and the Place of Pressure, the Distance of the Spring’s Hollowness would be just half the Distance of the Spring’s Play, to wit, the One-eighth Part of an Inch; but as the Spring does not quite reach up to the Axis, and reaches much below the Place of Pressure, the Hollowness at the Place where the Setting-screw bears against the Middle of the Spring at D, is considerably nearer to the Place of Pressure than to the Axis of the Tongue; this Hollowness of the Spring at the Setting-screw may be something more than the One-eighth Part of an Inch, to give the Spring a Quarter of an Inch Play: but it seldom has so much.

Fig. 4. in Plate 2. shews the Length and Thickness of the Steel Spring of a Turnep Seed-box: This serves both for a Tongue and Spring: It is made first strait, and then the narrowest End of it is turned round, till it reach to a, and forms the Cylinder A, thro’ which its Axis passes; but is not welded or joined to the other Part of the Spring at a: It is placed in the Box with the Cylinder Part underneath. The Face of this Spring is seen upon its Axis, mark’d K. in Fig. 5. Its Axis is to pass thro’ the Hole E, and screw into the Hole F, in Fig. 2. as is seen more plainly at a in Fig. 9.

As the Top of every Tongue ought to be even with the upper Edges of the Mortise, the Thickness of the Cylinder of the Brass Tongue causes the Hole in the Sides of the Mortise, into which it is held by its Axis, to be far enough from the Edges of the Mortise, to be bored and screwed without Danger of breaking the said Edges; but the Spring of the Turnep-drill being so very thin, there is some Difficulty in making the Hole so high, and near the Edges: To prevent which Danger, Fig. 7. shews the End of a small hollow Cylinder of Iron or Brass, of the Thickness of the Mortise; which, being put into the Cylinder A, in Fig. 4. raises the Spring higher above the Hole; so that it may be made as low in a Turnep Mortise, as that is which holds the Brass Tongue in the Wheat-drill. But we do not always use this inner Cylinder; but must then take the more Care in boring the Hole, or else it will burst out at the Edges of the Mortise.

For, instead of this, we may use a Bit of Woolen Cloth of the Breadth of the Mortise, glued on to the Bottom of the Hopper, which, filling the Vacuity above the Steel Tongue, prevents any Seed from running over it, though the Holes are bored as low in the Mortise as if the Cylinder Fig. 7. were to be used.

Its Shape must conform to that of the Brass Tongue already described.

The Degree of its Stiffness is known by weighing, as has been directed for the other Spring; and being laid with its Face downwards over a Chink, with a small Piece of Wood of the Thickness of a Barley-corn at Each end, and a String taking hold of its Middle, and descending thro’ the Chink, the Weight of Five Pounds, tied to the End of the String, will just bend the Spring, till it touch the Edges of the Chink; and this is the Stiffness of a Spring that has performed well, for many Years, in drilling of Turnep-seed.

The SETTING-SCREW.

Fig. 6. is the Iron Setting-screw, which passes thro’ the Hole in the Fore-end of the Mortise, Fig. 2. and passes up to the Middle of the Spring by the prick’d Line p q in the same Figure. The Use of this Setting-screw is, to increase or diminish the Proportion of Seed to be turned out by the Notches; and this it does by forcing up the Spring and Tongue (where there is one) nearer to, or farther from the Spindle, whereby the Seed-passage is made wider or narrower, as is shewn by the Three prick’d Lines in Fig. 2. and Fig. 3.

Observe, that the prick’d Line p q, Fig. 2. (being the Mortise of the Turnep-box) stands higher than the same Line doth in Fig. 3. which is the Mortise of the Wheat-box. The Reason of this Difference is, because the Spring in the Wheat-box bears at its lower End against the Tongue below the Seed-passage, and at its upper End below the Axis of the Tongue, whereby the Middle of that Spring is lower than the Spring of the Turnep-box, which, being both Spring and Tongue, bears against its Axis above, and against the Seed-passage below; therefore its Middle is higher. This Setting-screw should be placed perpendicular to the Tongue when at its mean or middle Distance from the Spindle, which may be supposed to be the middlemost of the Three mention’d prick’d Lines. This Setting-screw ought to be smooth and round at its End, which bears against the Spring; for, if it should have sharp Corners or Edges, the Spring might be wounded by them, and in time might break there, being press’d by every Notch that turns against it; and, as I have computed it, a Spring undergoes One hundred thousand of these Pressures in one Day’s Work; and yet, in my whole Practice, I have had only one Spring broken, and that was in drilling a large Sort of Peas with a Wheat-drill, and was occasioned by a jagged End of the Setting-screw, which was not placed perpendicular to the Spring, by which means the rough End of the Screw made Scratches against it a Quarter of an Inch long, and so deep, that the Spring broke off there: Let not this Setting-screw be any longer than just to force the Tongue up to the Spindle; for, if it should be longer, an ignorant Driller might happen, by the Force of the Screw, to break the Tongue, or its Axis; but in the Turnep-drill, which has only a Spring instead of a Tongue, the Setting-screw may be a Thread or Two longer; because the Spring will yield a little to it, after it touches the Spindle, and is sometimes of Use in that respect, when the Notches are too large. This Screw must be of such a Bigness, that it may not be in Danger of bending; for if it should be bent, it could not be screw’d up with any Certainty, because its End, being crooked, would be below its Place at one Half-turn, and above it at the other Half-turn, and so the Spring might be set farther from the Spindle instead of nearer, and nearer instead of farther, by the Crookedness of the Setting-screw. Its Head may be made with a Notch in it, to be screw’d in with a Knife, or else with a Head like a T, to be turn’d with the Fingers, which I think is best, especially for a Wheat-drill; because as the Brine and Lime, which stick on the Wheat, grow drier, it will run faster; and therefore the Setting-screw must be frequently screw’d in to lessen the Seed-passage.

The Seed-passage, or Place of Pressure, is where the Seed passes down betwixt the Spindle and the Tongue; and is in that Part where they are nearest together; for there the Seed is press’d hardest by the Force of the Notches, which carry it down: And this Passage is higher or lower, as the Tongue stands nearer or farther from the Spindle; for as it stands wider, it becomes nearer to perpendicular to the Top of the Mortise, and then the Seed-passage is higher; and when it stands nearest to the Spindle, then the Seed-passage is lowest. This appears in Fig. 3. by the Three prick’d Lines a n, a o, and a p.

The Spindle, with its Notches, is best shewn where it is large, and made of Wood, as that of the Wheat Seed-box; it is a solid Cylinder that passes thro’, and fills the great Hole, or hollow Cylinder, of the Seed-box; it is of various Lengths, according to the Distance its Wheels go asunder; it is always in large Boxes the Axis of Two Wheels, and turns round with them, as the Axis of the One Wheel of a Wheelbarrow does with that: These Wheels, by their Circumferences, measure out the Ground over which they carry the Seed-box, and, by the Notches in their Axis, deliver down the Seed equally, whether they move swift or slow; because an equal Number of Notchfuls of Seed will be deliver’d thro’ the Seed-passage at each Revolution of the Wheels.

The Notches resemble those in the Hinder-Cylinder of a Cyder-mill, which break the Apples by turning against the Notches of the Fore-cylinder, as our Notches turn against the Tongue; and bruise the Apples which come betwixt them, as our Notches might sometimes bruise soft Seeds, if the Tongue stood close to the Notches, without any Spring behind it to give Way to their Pressure, and return the Tongue again to its Place, at every Interval betwixt Notch and Notch.

The best Way, that I can think of, to shew the making of these Notches, is by a Section of the Spindle at right Angles, in the Middle of the Notches, as in Fig. 4. of Plate 3. which is a Circle whose Circumference is cut off by Six Notches; which shew the different Sort of Notches, that increase or diminish the Proportion of Seed to be carried thro’ the Seed-passage by them: The Length of the Notches we never alter; but make them always parallel to the Axis of the Spindle, and of the Length of the Distance there is between the lower Ends of the opposite Axes transversi of the Ellipses, or great Holes, of the Mortise; for if any Part of the Surface of the Spindle should be betwixt the End of a Notch and the Hole, one or more Seeds coming betwixt that Surface and the Tongue, might hold it open, and prevent its pressing against the Notch, to hold the Seed therein from falling without the Turning of the Wheels.

This Proportion of Seed is alter’d by the Number of Notches, and by their Depth or Breadth, or by both. b c is the Depth of a Notch, which we call its Side; and is that which takes hold of the Seed, and carries it down thro’ the Seed-passage. The Manner of cutting this is seen by its being a Portion of the Radius A c. The Bottom of a Notch is made in different Forms: As, first, it may be convex, as is shewn by the curve Line b d. We may enlarge the Capacity of this Notch, by taking off the Convexity of its Bottom, as in the Bottom of the Notch shewn by the Line e f; and if we would increase it more, we make it concave, as g h.

The convex Form is best for turning out a great Proportion of Seed; because such a Bottom may be broader than one of any other Form, in a Notch of the same Depth and Capacity; and such a Notch, having its Capacity more in Breadth than Depth, will be less liable to let fall any Seed without the Turning of the Wheels, than a Notch that is deeper and narrower, except it be very narrow, which it cannot be for throwing out a large Proportion of Seed; for a great Number of Notches cannot have altogether the same Capacity as a lesser Number of the same Depth may. The concave Notch, if it were as broad as the convex may be, would make the Interstice, that is before it, liable to be broken out, and so Two Notches would become One; but the Convexity of the other supports the Interstice like an Arch, and for that Reason may be made to reach almost quite to the Notch that is before it, without that Danger.

But of whatever Sort or Dimensions one Notch is made, all the rest should be the same exactly; and consequently, the Interstices (or Intervals) between Notch and Notch, of which the Line f c, being an Arch of the Circle, is the Breadth, must be equal, and cannot be otherwise, if the Notches are all equal and equidistant, as they appear in the adjoining Fig. 5. which is a Section like the former, and shews Six Intervals, with their Six Notches, of the Size wherewith we drill St. Foin with high Wheels; but when we would drill very thin, it is better to have but Four or Five Notches instead of Six.

But these cannot be equal, unless the Notches are all of equal Breadth, and equidistant from one another; and if they are otherwise, the Seed will not be equally delivered to the Ground.

Fig. 6. shews a Notch of the Spindle. a b is the upper Edge of the Side of the Notch, being always an acute solid Angle. c d is the Edge of its Bottom, being always an obtuse Angle. e f is the Angle made by the Side and Bottom, and is always shorter than the aforesaid Two Edges, by reason of the Obliquity of the Two Ends; this Angle is never obtuse, except when the Bottom of the Notch is concave. These Three Lines must be parallel to the Axis of the Spindle.

Fig. 7. is one End of the afore-described Notch; the Line a b being joined to the Line f d of Fig. 6. and the Line a c, being joined to the Line b f in Fig. 6. would be the End of that Notch in its proper Posture; and then the Line b c, being an Arch of the cylindrical Spindle, would be the Edge of the upper End of the Notch. a b c, being the Area of this End, is a Plane, and, when in its Place, makes an Angle of Forty-five Degrees with the Axis of the Spindle. The other End is the same with this in all respects, except that, being opposite to it, it is inclined to it in an Angle of Ninety Degrees, at the bottom Angle of the Notch, at the Line e f in Fig. 6.

Fig. 8. is a Notch lying with its Ends near it, and is of the same Dimensions with those appearing in the Seed-box, Fig. 3.

The Cover B appears with its upper Surface rightly placed in the Mortise, in Fig. 3. of Plate 3. where its Breadth is shewn to be the same with that of the Mortise; but its Shape, and other Dimensions, are best seen in Fig. 3. of Plate 2. where s t is its Length, and reaches from the Hinder-end of the Mortise, to within the Tenth of an Inch of the upper End of the Axis transversus of the Ellipsis; its greatest Depth is from v to w, and is made so deep, that its Bottom, at w, bearing against the End of the Mortise, may prevent its Point, which is at t, from sinking down to touch the Spindle, which it neither must do, nor be so high above it as to suffer a Seed to pass between the Spindle and it, tho’ the Seed is not apt to pass that Way, because the Notches throw it forwards from the Cover. z is the Hole, thro’ which an Iron Screw-pin passes, and screws into the opposite Sides of the Mortise, to hold it firm in its Place: ’Tis made so thin betwixt x and y both for Lightness, and that the Seed may come the more freely to the Notches, without Danger of Arching at that End. The Use of the Cover is to prevent any Seed from falling down behind the Spindle.

Fig. 10. Plate 2. is the Fore-end of a Wheat Mortise, with its Hole A, thro’ which the Setting-screw is screw’d, and passes up to the Back of the Tongue by the Line q r in Fig. 3.

Fig. 9. in Plate 3. is the hinder End of a Wheat Mortise, which by its prick’d Lines, and the Two right-angled Triangles they make, shews the Bevel of the Mortise, and also its Depth; it also shews the Difference of the Bevel of the Mortise, and that of the Tongue, Fig. 1. which is placed against it: These Figures having been already demonstrated in the Description of the Turnep Mortise, and in these, I need say no more of it, but that I think these last-mention’d Figures sufficient Directions for understanding and making the Mortise of a Wheat-drill.

Fig. 3. of Plate 3. exhibits to View a Wheat Seed-box, with its Appurtenances, standing upon its Bottom; B the Brass Cover; C the Tongue hanging upon its Axis; c the End of the Iron Screw that holds on the Spring, coming thro’ the Tongue, and filed smooth with it; a, a, a, are Three Notches of the Spindle, with their bevel Ends; b, b, are Two Interstices betwixt the Notches.

Hitherto we have been speaking of the Parts contained in the Wheat Seed-box; let us now come to the Parts containing: As, first, d e f g is the upper Surface of the Brass Seed-box, shewing the Top of the Mortise, and what it contains; h h h, and h h h, shew the Ends of the hollow Cylinder, and its Bases coming out on each Side, farther than the Box; for if it did not project farther out than the Sides of the Box, the Surface of it would be so narrow, that it would cut the wooden Spindle by the Friction made between it and the Spindle; but the Surface, being of this Breadth, never wears into the Spindle, but makes it smooth and shining; i i i, and i i i, shew a Portion of the wooden Spindle (of an Inch and an half Diameter) coming out of the hollow Cylinder, on each Side of the Brass Box.

The Spindle is kept from moving end-ways, by Wreaths, in the same manner as the Axis of a Wheelbarrow is; which Wreaths shall be described together with the Hopper. k is the Hole by which the Fore-end of the Seed-box is held up to the Bottom of the Hopper, by a Screw and Nut. l is the Hole where the Hinder-end of the Box is held up, in the same manner as the Fore-end is. m n o p shew where the Two Halves of the Seed-box are joined together.

Fig. 10. shews the Outside of One Half of the Brass Seed-box. A A A shew the Thickness of the projecting Base of the hollow Cylinder, which is made the thicker, to the end that the Hole may be bored large, and made an Inch and Three Quarters Diameter, when a Spindle that is to go therein is required to be of that Bigness, by reason of its extraordinary Length, as it is in the Fore-hopper of the Wheat-drill. B C shews the Thickness of the Ends of the Seed-box, whereby it is held up to the Bottom of the Hopper; if they are not quite a quarter of an Inch thick, they will be strong enough; especially C, which is the hindermost, and which is never pull’d down by the Turning of the Spindle, but is rather raised up by it.