Chapter XIV: Preface (14)

The Spring must bear against the Back of the Tongue at each End, and lie hollow in the Middle: But the Degree of Hollowness of the Spring is very material; for thereon depends the Distance of the Tongue’s Motion towards the Spindle by Force of the Spring, and back again quite to the Setting-screw, by the Seed that is pressed against it by Force of the Notches, when they are moved by the Wheels; because the more the Spring is curved, the farther will it thrust the Tongue from its Middle, if its Strength be superior to the Force that resists it, as it ought to be when a Notch is passed and before the next: This Motion of the Tongue is called its Play.

In order to measure the Distance (or Quantity) of this Motion, we must consider, that the Tongue, moving on its Axis above, describes with its lower End the Arch of a Circle, the Chord of which Arch is the Measure required.

To measure this by the Angle the Tongue makes at its Centre, would be no Rule for making Boxes; because some Tongues are longer, some shorter, in proportion to the different Diameters of the Spindles they move against; and yet the Play of the shortest must be as much as that of the longest, that is, it must describe as great an Arch at the Place of Pressure (described in _Fig._ 3. _Plate_ 2.); and therefore the shortest Tongue would make the greatest Angle.

A short and easy Way, then, for a Mechanic to measure, is thus: Screw in the Setting-screw until the Tongue come within a quarter of an Inch of touching the Spindle; then take out the Spindle, and from the Centre of the Hole draw a Line on the Side of the Mortise, perpendicular to the Tongue, and at the Tongue’s Edge make a Mark with the Compasses, or a Pen; then force back the Tongue against the Setting-screw as far as it will go (that is, until the Spring touch the whole Back of the Tongue); produce the said Line to the same Edge of the Tongue, or set the End of the Rule thereon, and draw another Line, by the Rule, from the Mark to the Edge of the Tongue, when farthest back, and there make the second Mark. The Ruler used this Way will shew both the Perpendicular, and the Measure.

But yet a quicker Way is, to set the Tongue, by the Setting-screw up to the Edge of the Hole; and, when it is forced back, measure from the Tongue to the nearest Part of the Hole, which will ever be a perpendicular Line drawn from the Centre of the Hole to the Place of Pressure above-mentioned, and make another Mark there: Now the Distance between these Two Marks is the Measure (near enough) of the Tongue’s Play at the Place of Pressure. Tho’ this Line drawn on the Side of the Mortise be not exactly perpendicular to the Surface of the Tongue, but only to its Edge; yet the Difference is next to nothing, and not to be regarded.

If its Measure be a quarter of an Inch, it is what Experience shews to be of a good Size for all Corn and Peas; a little less is no Harm, but greater is the most fatal Error, into which most of the Pretenders to the making of this Machine have fallen; they give the Tongue half an Inch, sometimes Three quarters of an Inch Play. The Mischief of this Error is yet farther increased, if the Spring be weak, if the Mortise have too great a Bevel, or if the Angle made by the Tongue at the upper Edge of the Mortise be too acute.

When the Tongue has too great Play, the Seed is apt to be turned out too fast, or else too slow, in spite of the Driller. For when the Tongue is set at its due Distance from the Spindle, and is thrust quite back by the Seed pressed against it by the Turning of the Notches; but the Spring being unable to return the Tongue to its former Place at such a Distance, at the time of passing the Intervals which are betwixt the Notches; then the Space between the Spindle and the Tongue being too open, the Seed is sent down too fast.

To prevent that, they set up the Tongue to the Spindle; and then, as often as the Spring happens to overcome the Force of the Seed’s Pressure (as sometimes it will), it is sent out too slowly.

The Inequality of the Running of the Seed makes such Boxes useless, which the Expence of Two-pence (for another Spring, or new Seasoning of that) at most would rectify, if the Maker understood how to mend his own Work. If time did permit, more should be said on this Point, because I find it is the _Pons Asini_ of a Workman. Sometimes it may be prevented, when the Spring is too hollow, and gives too much Play. Screw the Screw, that holds it on the Tongue, down closer, so that the lower Part of the Screw’s Head press against the Spring, and thereby force its Middle nearer to the Tongue, until you find its Play lessened to its just Distance.

The Spring, remaining in this compressed State, has lost the weakest, and retains only the strongest, Part of its elastic Force. Therefore, if you find it then too stiff, make it weaker by Filing or Grinding, or else put another into its Place, which is honestly worth no more than Two-pence.

This Holding-screw has a pretty broad Head, and is screwed in by a Notch, like the Screw-pin of a Gun-lock.

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[263]; but must then take the more Care in boring the Hole, or else it will burst out at the Edges of the Mortise.

[263] 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[264]: 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_.

[264] 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[265], 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.

[265] 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.

D is the Head of the Counter-screw, to be turn’d by the Fingers, to press against the Side of the Setting-screw, to keep it from turning of itself, when it is worn loose.

E is the Hole for the Axis of the Tongue. F is the Hole of an Iron Screw-pin, which both holds the Cover to its Place, and also the Two Halves of the Box together. G is the Hole for another Screw-pin, which holds the Two Sides of the Box together. H and I are Holes for Two other Screw-pins, which likewise hold the Two Halves of the Box together, and are placed one above, and the other below, the Setting-screw; for otherwise that Screw, and its Counter-screw, might force open the Joining of the Box, and then the Setting-screw might be loose, and the Bevel of the Box might be altered; but these Screws, being one on each Side of it, prevent this Inconvenience.

_Fig._ 8. in _Plate_ 2. is one Half of a Brass Turnep Seed-box, lying with its Inside uppermost, which shews the left Side of the Mortise, and half the Fore-end, and half the Hinder-end, of the Mortise, and half of each Screw-pin Hole, by which it is held up to the Bottom of the Hopper. A is half the Hole of the Setting-screw, shewing in the Middle of it the End of the Counter-screw. B is half the Hole, by which the Steel Spring-cover is held in with a Screw. All the other Holes are for the same Purposes, as have been shewn in the Wheat Seed-box.

_Fig._ 9. is the whole Turnep Seed-box, standing upon its Bottom; Part of its Steel Spring-tongue appears in its Place, as also some of the Notches of the Spindle; but more especially the Cover A, which differs from the Cover of the Wheat Mortise, this being a very thin Spring, whose lower End just reaches to touch (but not to bear upon) the Spindle at the upper End of the transverse _Axes_ of the Ellipses; the Mortise being filed away at the End, in order that the upper End of this Spring, and the Screw which holds it, may not lie above the upper Surface of the Box. This Spring is made very weak, to the end that, if by any Chance a soft Seed should stick in a Notch, and be turned round, this Spring might suffer it to pass by without breaking it. B, C, are the Two Flanks or Sides, made necessarily of this Breadth, for bearing against the Wood of the Bottom of the Hopper, to prevent the Seed from falling out betwixt the Wood and the Brass, and that the Hole in the Hopper may be broader than this narrow Mortise of the Seed-box. The left Flank B, being next the wide Side of the Hopper, lies all open, except on the outside of the pricked Lines, where it is covered by the Wood of the End of the Hopper, when it is screwed on to its Place; but the Flanch C, on the right Side, will be all covered by the End of the Box, that will stand upon it, and will reach to the pricked Line that touches the Edge of the Mortise. D is the End of the Setting-screw, appearing in its Place with a Notch, whereby it is to be turned by a Knife; but I think it better to have an End like a T, to be turned with the Fingers. E is one End of the hollow Cylinder, which projects beyond the Flanch, that there may be more Room for the Crank to turn (without striking against the End of the Hopper, or against the Flanch) on the Outside of the Box or Hopper; and for that, the longer this Cylinder is, the better the Brass Spindle will turn in it.

_Fig._ 11. is the Spring-cover, with its Hole, whereby it is screwed into its Place, as it is seen marked A, in _Fig._ 9.

_Fig._ 12. is the Setting-screw pointing against its Hole, its Head being flat, that it may be turned by the Finger and Thumb.

_Fig._ 13. is the Counter-screw, to be turned in the same manner.

_Fig._ 5. shews the Brass Spindle of the Turnep Seed-box, and the Manner of turning it against its Steel Tongue, or Spring; which Manner is different from that of turning the larger Spindles for Boxes of a larger Size, such as the Wheat Seed-box.

This Spindle[266], being but half an Inch Diameter, is too small to be turned by the Two Wheels, as the larger Spindles are; not only because it would be in Danger of breaking by the Weight of the Hopper, and by the Twisting (or Wrenching) of the Wheels; but also because it would soon become loose, by wearing the hollow Cylinder thro’ which it passes; and it would be apt to open the Brass Flanches from the Bottom of the Hopper, whereby the Seed might run out, beside several other Inconveniencies; all which are prevented by turning the Spindle in the manner shewn in this Figure; for here the Spindle never presses against the hollow Cylinder, with any greater Force than that of its own Weight, which is so very little, that the Friction made by it is next to nothing.

[266] I believe, if it were less by a Fourth or Third of its
Diameter, it might be better, as being more proportionable to the
Smalness of the Turnep-seed. I have had the Mortise much wider; but
it cannot well be made much narrower, whilst the Tongue is of this
Fashion; for this Steel Tongue, if narrower, would either be too
stiff, or else apt to break, nor would there be Room in the Mortise
for a sufficient Setting-screw to follow it. But there is another
Fashion, wherein a narrower Brass Tongue has a broad Spring behind
it; and when it is in this Manner, the Mortise may be a Fourth of
the Breadth of this. I have had many of these when I made my Boxes
in Wood; but cannot describe them by these Cuts; neither are such
narrow Mortises necessary, unless it were for drilling Tobacco seed,
Thyme-seed, or some other Sort of an extraordinary Smalness.

A the Spindle, exactly fitting the Bore of the hollow Cylinder; which, when it enters the said Cylinder at its left End, in _Fig._ 9. will be stopped by the Wreath B B B; which Wreath, being circular, is cast on the Spindle, and is Part of it; the other End of the Spindle will then appear without the right-hand End of the said hollow Cylinder, at E in _Fig._ 9. and is kept there by the Wreath _Fig._ 14. which is to be put on upon the End of the Spindle, until it come to the Shoulder at _a_, which Shoulder is exactly even with the End of the hollow Cylinder; so that this Wreath will touch the End of the said Cylinder by its whole Surface. Then, to fix in this Wreath from coming off, we make use of the Slider, _Fig._ 15. whose Two Claws A, B, being thrust down by the Two Notches of the Spindle, at _b_ and _c_, until its other Part C, which is perpendicular to its Claws, comes down to the Flat of the Spindle, and environs one half of the Hole, covering the Part of the Flat which appears of a darker Colour; and then the upper Part of C, in _Fig._ 15. makes one level Surface with the Flat D of the Spindle; and then the Iron Fork E, being screwed into the Hole F, holds down the Slider fast, so that it cannot rise up; and then the Spindle, being in its Place, will run round without moving endways, being confined by these Wreaths.

The Spindle being thus placed, so that it may turn easily, we place the Seed-box upon its Flanches with its Bottom upwards; and then setting one sharp Point of a Pair of Compasses, or some such Instrument, upon the Spindle, within the Mortise, close to the Edge of the Hole or Ellipse at the End of the transverse Ax, turn round the Spindle, until the said Point makes a Mark round the Spindle, which will be a Circle; by the same means make such another Mark at the opposite Ax; then unscrew the Fork, and take out the Slider, pull off the Wreath, and take out the Spindle, and cut the Notches between the Two said Circles and Marks; the Edges of the Ends of the Notches must be Arches of these Circles. These Notches should differ from those already described in the Wheat-drill, in nothing but the Smalness of their Dimensions; their Depth should be about the Thickness of a Turnep-seed, or something deeper. The Breadth of their Bottoms is uncertain, and must be greater or less according to their greater or less Number; but we commonly have Seven or Eight Notches, and make them about the Breadth in which they appear in this Figure; but whatever their Number be, they must be all equal, and so must all their Interstices.

G is the End of a wooden Spindle, thro’ which passes the Iron Crank H, and is fastened to it by its Screw and Nut, at _d_; Part of which Crank enters the Wood at _e_, which prevents its Turning in the Spindle.

This Crank, by its other End, passing thro’ the Two Legs of the Fork E, and equally distant from the Top and Bottom of it, turns the Spindle by the Motion of the Wheel which is fixed on the other End of the wooden Spindle. If this Crank were to turn the Spindle by a single Pin, instead of this Fork, the Seed could never be delivered out equally to the Ground; for as soon as the Pin began to descend, and decline from being perpendicular to the Horizon, it would, by its own Weight falling down, turn the Spindle half round in a Moment, and there remain with its other End downwards perpendicular to the Horizon under the Spindle, until the Crank reached it there, and so no Seed would be turned out by one Semicircle of the Wheel, and a double Proportion would be turned out to the Land that was measured by the other Semicircle; but the hinder Leg of the Fork, bearing against the hinder Part of the Crank, prevents this Inconvenience.

The Line _f g_ is Part of the Surface of a Board, thro’ which the wooden Spindle passes, and by which it is held in its Place; as shall be shewn hereafter.

The Axis of this wooden Spindle ought to fall into a Line with the Axis of this Brass Spindle; but, unless Care be taken to prevent it, the wooden Spindle will so much wear the Hole thro’ which it passes, and be worn by it, as to have Room in the Hole to deviate from this Exactness, and may descend so low, that the Crank may come out of the Ends of the Fork; and for this Reason it is, that the Fork is made so long as it is; but when this wooden Spindle does, by the Contrivances hereafter shewn, keep its Axis in a Line with the Axis of the Brass Spindle, or very nearly so, then the Legs of the Fork need be no longer than half an Inch; and in that Case, the Joint of the Crank, which is perpendicular to the Spindle, must be shorter, or else descend deeper into the Wood, so that its End, which turns the Fork, may be in the Middle betwixt its Bottom and the End of its Legs.

The Use of the other End of the Spindle is this: When we have a mind that it should be turned by the left Wheel instead of the right, we screw in the Fork into the Hole I, and place a short Screw in the room of the Fork, to hold down the Slider.

_Note_, It is not absolutely necessary, that the hollow Cylinder, which appears on the Sides of the Seed-box, should both, or either of them, project farther than the Flanches; but I think it better that it should do so, at least, on that Side which is next to the Fork.

This Cylinder should be bored as true, and as even, as the Barrel of a Fusil is bored: and the Edges and Surfaces of its Ends must be smooth, and without Jaggs, to the end that the Wreaths may turn glibly against them.

The Figure or Shape of all Sorts of Seeds disposes them, more or less, to form an Arch, when they are pressed from above, and confined on all Sides.

The most effectual Way to prevent this is, to take care, whenever many Seeds are to descend together by their own Gravity thro’ a narrow Passage, that such Passage be never narrower downwards than upwards; but, on the contrary, that it be wider downwards, on some or one of its Sides; in which Case, if the Surfaces of all the Sides of this Passage be smooth, it is impossible, that Seeds should of themselves form an Arch therein.

On this Maxim depends the infallible Performance of a Drill, and from hence are derived the Uses of the Bevel of the Mortise: What I mean by the Word Bevel, in general, has been already defined.

The Bevel of the Mortise of the Seed-box is that Inclination of its Sides, whereby it is wider downwards, and narrower upwards; by which means the Seed is prevented from arching in the Mortise before it descends to the Notches of the Spindle. And this is the First Use of our Bevel; for this Arching might happen in the Mortise, if the Planes of its Sides were parallel to each other; and would be unavoidable, if their Inclination were downwards, as it is upwards; but these Planes opening downwards, the lower the Seed descends, the more Room it has to expand; so that the very Weight, which would otherwise cause it to arch and stop, does by means of this Bevel force it to descend to the Notches, and then it is safe from all manner of Danger of stopping. The Ends of the Mortise are at such a great Distance from each other, and the Cover so very thin, as to lie almost even with the upper Part of the Spindle, that the Seed can never form an Arch that way; or, if it did, the continual Motion of the Tongue would immediately break it down at the Fore-end of the Mortise.

The Second Use of this Bevel is, that it gives room for the Tongue to be in the same manner bevel, tho’ in a less Degree: By this means, the Seed cannot by any Impediment be stopped in its oblique Descent to the Notches, from the Fore-end, and all that other Length of the Mortise, along and upon the Surface of the Tongue.

But if the Mortise had not this Bevel, the Tongue could not have it; for then either the upper Surface of the Tongue must have no Bevel at all, which would destroy the Two empty Triangles which ought to be on its Sides; or else it must have a Bevel the contrary Way (_i. e._ a Bevel reversed), and be narrower downwards than upwards, which would cause the Seed to arch thereon, and hinder its free Descent to the Notches.

A Third great Use of this Bevel is, that, besides the Bevel of the Tongue aforementioned, it gives place for Two empty Triangles, one on each Side the Tongue, which have each its vertical Angle extremely acute at the Axis of the Tongue, and have their Bases at the Bottom of the Mortise, and of the Tongue: These Triangles are also Bevels, which consist of the Difference, or Complement, of the Bevel of the Tongue, and that of the Mortise, the latter being about One-third greater than the former; _i. e._ One-third of the whole Bevel of the Mortise is divided between these Two Triangles, to each a Sixth Part; so that if the Angle of Inclination of the Sides of the Mortise were Nine Degrees, then the vertical Angle of each of these empty Triangles would be of One Degree and Thirty Minutes, and Six Degrees, would be left for the Bevel of the Tongue. And these triangular Spaces help to secure the free Motion of the Tongue, and free Descent of the Seed down its Surface; because they permit no Impediment to lodge in them, they being, by means of the Bevel of the Mortise, wider downwards, both obliquely and perpendicularly, so that no Dust, nor whatever else happens to get in betwixt the Tongue and the Side of the Mortise, can rest there; for it will be immediately removed thence by the Motion of the Tongue, and its own Gravity, and either thrown perpendicularly down, or else obliquely to the Notches, and the first Notch that takes it will carry it out at the Seed-passage.

The Fourth Use of the Bevel is, that thereby the Sections of the hollow Cylinder (before described) do form Ellipses instead of Circles; which they must have been, if cut parallel to the Bases of that Cylinder; and the Sections must have been thus parallel, had the Mortise been without any Bevel.

Now the Two Semi-ellipses, which are on the Fore-sides of their longest Axes or Diameters, and next to the Tongue, are opposite to, and do still uniformly depart from each other, even from the upper End of their said longest Axis, until they arrive at the lower End of the same Axis, which is below the Seed-passage, as its upper End is very near the Cover.

This Opening of these opposite Semi-ellipses makes it impossible for any thing, of itself, to get into the remaining Parts of this hollow Cylinder, betwixt them and the solid Cylinder, call’d the Spindle, which turns continually therein, when the Wheels are going: For you will see, that if you make a Mark on the Spindle, close to the Side of the Mortise, at the upper End of the longest Ax of the Ellipse; and then turn the Spindle until this Mark come against the lower End of the same Ax; and there make another Mark on the Spindle, close to the Side of the Mortise; and draw a Line from one Mark to the other, parallel to the Ax of the Spindle, which will be the Measure of that Part of the Bevel of the Diameter of the Hole; every Point in this Line will, by an intire Revolution of the Spindle, generate a Circle, which will cut the Ellipse in Two Places, once on the Foreside of its longest Axis, and once on the Back-side or hinder Half of it; and that all these Points, in this Surface of the Spindle, described by these Circles, will enter the Hole, by the said hinder Semi-ellipse, as the Spindle there turns upwards (as it always does); and they will all again come out on the fore Semi-ellipse, as they descend towards the lower End of the said Ax of the Ellipse.

As these Points thus come out of the Hole, or (if I may use the Expression) as they emerge, they oppose every thing that would enter the Hole, they still moving from the Hole, and push away from it whatever they meet; nay, if any thing were in the Hole, these Points (whereof this Surface consists) would bring it out by this Semi-ellipse, which is always press’d by the Seed when the Drill is at Work; but as these Points immerge by the other Semi-ellipsis which is behind the Spindle, they can carry with them into the Hole nothing but Air, because the Cover never suffers any thing else to come there from above; and the Seed falls out of the Notches by its own Gravity, just before it reaches the lower End of the transverse Ax, being the Place where the opposite Ellipses are farthest asunder; and none of it is ever carried so far back as the hinder Semi-ellipses; and therefore nothing can be carried into the Hole from below.

Thus that Part of the Surface of the Spindle will keep the Hole empty and clear, before ever any Notches are cut; but when the Notches are made on the Spindle, they have yet a much greater Force to drive and expel whatever would enter the Hole, their Shape being such as nothing can enter against their bevel Ends; but what is at their Ends will be thrown presently into the Mortise; insomuch that when a Spindle has been too little for the Hole by a Quarter of an Inch, that is, a sixth Part of the Diameter of the Hole, it will perform very well in drilling large Species of Seeds; and when the Mortise is run empty, nothing at all is found in the Hole, it being thus kept void and clean by the Notches.

_Note_, That what is here, and elsewhere, said of the Ellipse of the one Side of the Mortise, must be understood the same of its opposite Ellipse, on the opposite Side of the Mortise.

All these Advantages accruing from this Bevel of the Mortise, I believe that, without it, all Attempts of making a Machine to perform the Work, which this does, would have been vain.

There is also within the Mortise unavoidably another Bevel, which is as the Reverse of the former, and notwithstanding is as useful; and this Bevel is, the Inclination which Part of the curvilineal Surface of the Spindle, beginning a little above the fore End of the shortest Diameter of the Ellipses, and descending down to the Seed-passage, has to the lower Part of the Surface of the Tongue opposite against it. These Two Surfaces meeting one another below, when the Tongue is set up close to the Spindle, form a mix’d Angle, which stops up the Seed-passage, except when a Notch comes against it.

When the Tongue is set from the Spindle, to the Distance of several Diameters of one of the Seeds that are to be drill’d, this revers’d Bevel causes the Seed to arch at the Seed-passage, and stop there, till the Notches force it thro’, which would, without this Arching, fall out by its own Gravity, without the Turning of the Wheels.

The Seed arches here the more firmly, the more it is press’d upon by the incumbent Seed from above it; and the former Bevel (which I call the Bevel of the Mortise) permits the incumbent Weight to press the harder on the Seed that is near the Seed-passage; and this might be reckon’d a fifth Use of the former Bevel: For as it prevents the Seed from arching in any other Part of the Mortise, so it does, by the same means, cause it to arch the more strongly at the Seed-passage, which is sometimes (_viz._ when the Tongue must be set wide) as necessary, as it is for it to escape arching before it comes thither. And the more strongly this Arch presses against the Tongue, the more the Tongue by its Spring presses against it; and this Pressure being reciprocal and equal, the Seed cannot fall out spontaneously; for when the Passage is thus wide, if you throw into the Mortise a few Seeds, suppose Five or Six at a time only, they will all pass through immediately, without any Motion of the Wheels; but if you throw in a large Quantity together, there will only a few of the lowermost fall through, unless the Wheels do turn and throw them down by the force of the Notches.

Indeed we do not care to set the Tongue so very wide from the Spindle, unless it be when we are obliged to plant a very much larger Proportion of Seed than the Notches are design’d for, and when we have no Opportunity of changing the Wheels for such as are lower, nor of changing the Spindle for another that has greater or more Notches in it.

Four-and-twenty Gallons of large Peas are as proper a Proportion to drill on an Acre, as Six Gallons of Wheat are.

There are divers Ways to vary (_i. e._ increase or diminish) the Proportion of Seed; as, First, by the Setting-screw, with which we can, without any Inconveniency, set the Tongue so far from the Spindle, as to permit one Round of the Notches to turn out Four times the Quantity, as it will do when the Tongue is set close up to the Spindle; and thus we can vary the Proportion by innumerable intermediate Degrees.

Next, if we would increase the Proportion yet farther, we can inlarge the Notches; but we cannot add to their Number, unless there be room to double it, by making a new Notch between every Two; but we cannot diminish the Proportion of Seed by the same Notches, because they cannot be made lesser or fewer.

If we would make any other Alteration in the Proportion of Seed by the Notches, it must be done by making another Set of them; which we may do, because the wooden Spindle may have Three Rows of Notches in it, of which we may use either, by moving the Wreaths and Wheels towards one End or the other of the wooden Spindle; as shall be shewn in the Descriptions of the Hoppers.

But as for the Brass Spindle of the Turnep-drill, we can have but one Set of Notches in it[267]: And therefore, tho’ we can increase the Proportion of Seed by enlarging the Notches, or perhaps by doubling their Number; yet we cannot lessen the Proportion of Seed by the Notches, unless we have a new Set of them, and that will occasion a Necessity of having another Spindle; but, as to the Setting-screw of the Turnep-drill, it will increase the Proportion of Seed with the same Notches, much more than the Setting-screw of the Wheat-drill will do.

[267] But by putting on a Wreath (that is a little broader than the
Mortise) upon the Spindle (made longer for that Purpose) we can, by
changing this Wreath from one End of the Spindle to the other, have
Two sets of Notches of different Sizes, and of different Numbers in
it: Or if we would have Three Sets, we need only make Use of Two such
Wreaths, and let the Spindle be long enough to receive them. So we
may use which Set we please.

Tho’ several Sets of Notches may be useful to those who drill many
Sorts of fine Seeds different in Magnitude in a very great Degree;
yet I never found more than one Set of Notches necessary in this
Spindle.

Nor have I used any more than one Set of Notches in one Mortise of
any Sort; but in a wide Mortise, there may be made a double Set of
Notches, consisting of Two Rows, all of equal Bigness, and half of
the Length, and double the Number of a single Row, one End of each
Notch reaching to the Middle of the Mortise, and pointing against the
End of an Interstice, that is between Two or its opposite Notches.