_Of the Drill-Boxes._
The Drill is the Engine that plants our Corn and other Seeds in Rows:
It makes the Chanels, sows the Seed into them, and covers them at the
same time, with great Exactness and Expedition.
The principal Parts of the Drill are, the Seed-box, the Hopper, and the
Plough, with its Harrow.
Of these the Seed-box is the Chief: It measures (or rather numbers) out
the Seed which it receives from the Hopper: It is for this Purpose as
an artificial Hand, which performs the Task of delivering out the Seed,
more equally than can be done by a natural Hand.
It is described, together with some of its Appurtenances, in _Plates_ 2
and 3.
_The_ MORTISE.
As the Seed-box is the principal Part of a Drill, so is the Mortise the
principal Part of the Seed-box.
The following Descriptions shew how this Mortise differs from a common
Mortise.
Fig. 1. _Plate_ 2. shews both the upper and lower Edges of a
Turnep-Seed-box, and the Manner how they are posited one over another,
_a b c d_ is a rectangled Parallelogram, and shews the upper Edges (or
Top) of the Mortise. _e f g h_, being a Figure of the same Denomination
with the former, is the lower Edges (or Bottom) of the Mortise. The
Line _e h_ is the Length of the lower Edge of the Hinder-end of the
Mortise. _a d_ is the upper Edge of the Hinder-end of the Mortise, and
posited just over the lower Edge of the same End. The Space between
the Line _a b_, and the Line _e f_, shews half the Excess whereby the
Bottom of the Mortise exceeds the Top in Breadth; as the Space on the
opposite Side, betwixt the Line _c d_, and the Line _g h_, shews the
other Half of that Excess, both which Halves, taken together, shew
the whole Bevel (or Angle of Inclination) described in _Fig._ 2. That
Part of the Line _a b_, from the Angle at _b_ to the Line _f g_, which
intersects it, shews the Excess whereby the Top of the Mortise exceeds
the Bottom in Length.
_Fig._ 2. Is the Mortise cut down by its Four Corners, and laid open.
_a b c d_ is a Trapezium, with Two parallel Sides, and mark’d A, the
right Side of the Mortise; its opposite Side _e f g h_, mark’d B, the
left Side of the Mortise; the Areas of both being true Planes[261].
[261] Take care that these opposite Sides be sure to be true
Planes, especially all that Part of their Areas, that is before the
transverse Axes of their Ellipses herein after described; for should
they be otherwise, the Bevel of the Mortise would be spoiled, and
so would the Ellipses, and the acute Triangles, on the Sides of
the Tongue; which how necessary they are to be true, is shewn in
the proper Place. Workmen are very apt to fail in this when they
file by Hand, and make these Sides of the Mortise convex instead of
plane. Therefore this might be done with less Difficulty, and more
Exactness, with a File placed in a Frame, whereby it might move upon
a true Level without rising or sinking of either End.
_d i k h_ Shew the Fore-end of the Mortise, mark’d C. _a l m e_ shew
the Hinder-end of the Mortise, mark’d D. _a d h e_ shew the Bottom of
the Mortise already described in _Fig._ 1. If these opposite Sides and
Ends were all raised up, until the Angle at _b_ join the Angle at _l_,
and that at _m_ join _f_, and that at _g_ join _k_, and that _i_ join
_c_, the Top of the Mortise would be formed, and the same with the
Parallelogram _a b c d_, in _Fig._ 1. and then the intire Mortise of
the Turnep Seed-box would appear in its true Form, standing upon its
Bottom.
This differs from a common Mortise, in that it is impossible to fit it
with a Tenon; because it is narrower above, and shorter below, as in
_Fig._ 1.
The Areas, or imaginary Planes, of the Top and Bottom of the Mortise,
are parallel to each other, but not equal.
Its Two opposite Sides are equal, but not parallel, by reason of their
Inclination to each other upwards, which is the Bevel hereafter to be
described.
The Two Ends are neither parallel nor equal, because the Hinder-end D
is perpendicular to the Top and Bottom, and the Fore-end oblique, and
therefore longer.
When Two opposite Sides, or Surfaces, are inclined to each other
upwards, I call that Inclination a Bevel; but when they are inclined
downwards, I call it a Bevel revers’d.
The Line _a e_, being the Bottom, or Base, of the Hinder-end D, by
being longer than the Line _l m_, shews that the Mortise is bevel.
The Two prick’d Lines _m n_ and _l o_, with the Line _l m_, and Part
of the Line _a e_, make a rectangled Parallelogram, which shews the
exact Depth of the Mortise, and forms on each Side of it a rectangled
Triangle, the one _m e n_, and the other _l o a_; which Triangles being
similar and equal, and their acute Angles at _l_ and _m_ being each of
Four Degrees, make the whole Bevel, or Inclination of the Sides of the
Mortise, to be of Eight Degrees, their Hypothenuses being the same with
the Sides of the Mortise.
This End D, being raised up to its Place, will be at right Angles
with the Plane of the Top and of the Bottom of the Mortise; which,
being both rectangled Parallelograms, prove that Bevel, or Angle of
Inclination, to be the same from one End to the other of the Sides,
which Sides are the Hypothenuses of those Two Triangles: But this could
not be proved by the Triangles in the opposite End C; because the
Bases being the same with the other, and having their Legs longer, the
vertical Angles at _k_ and _i_ are more acute. The Legs are longer;
because the End C, when in its Place, is not at right Angles with the
Top and Bottom of the Mortise, as the End D is.
The next thing to be described in the Mortise, is the Bore, great
Hole, or Perforation; which is best shewn in the Side of a Mortise
of a Wheat-drill, being larger, as in _Fig._ 3. wherein _c e b d_ is
the great Hole, and is a Section of an hollow Cylinder, that passes
through the Mortise, with its Axis parallel to the Edges of the Ends
of the Mortise: This Cylinder, being cut by the Side of the Mortise
obliquely, and not parallel to its Base, is an Ellipse.
The prick’d curve Line is a Circle parallel to the Base of the
Cylinder, and the curve Line _b d c e_ is the Ellipsis; and this Curve
is more or less elliptical (or oval) in proportion to the Angle of
Inclination, or Bevel, of the Sides of the Mortise.
Of this Ellipse the longest Diameter (or _Axis transversus_) _b c_ is
at right Angles with the upper and lower Edges of the Sides of the
Mortise.
Its shortest Diameter (or _Axis rectus_) _d e_, is the Diameter of
the Cylinder, bisecting the _Axis transversus_ at right Angles in the
Centre _a_; and is in this Figure one Inch and an half.
This Ellipse being concentric with the Circle, the Letter _a_ is the
Centre of both.
The Semi-ellipsis _c e b_ is the Part of chief Use; and therefore
the Edge must of Necessity be smooth, and without Flaws, as must the
Surfaces of the Sides of the Mortise betwixt the Ellipse and the
Fore-end.
The Tongue of the Seed-box (_Plate_ 3. _Fig._ 1.) differs from that
in the Sound-board of an Organ (from which I took the Idea of it)
in Shape, in Situation, and in the Manner of its being fix’d to the
Mortise.
The Tongue, in the Organ, is on its Surface a long Square, or
rectangled Parallelogram, a little broader and longer than the Mortise
(or Grove) it shuts against; but this Tongue on its upper Surface,
which is here turned downwards, being a Plane, is a Trapezium, of the
same Shape with the Fore-end of the Mortise just now described, except
that the Tongue has a less Bevel.
The Situation of that in the Organ is on the Outside of the Mortise,
which it shuts by its Spring behind it, and opens immediately by the
Finger of the Organist pressing down the Key to let in the compressed
Air to its Pipes; but this Tongue is situate within the Mortise of the
Seed-box, and placed almost, in a manner, diagonally; for, had it been
placed like the other, the Seed getting betwixt it and the Edges of the
Mortise, would not have given Way to its Shutting (as the Air does to
the other), but have kept it always open; which would have render’d it
useless for sowing of Seeds.
The Manner of fastening the Organ-tongue to its Mortise is by Parchment
and Leather glu’d to its Surface, and also to the Sound-board, at its
End which is opposite to that pressed open by the Key, and shut by the
Spring; but this our Tongue is held within the Mortise, and moves on
an Axis, which passes thro’ its upper and narrower End, which Axis is
the Pin A (which must be exactly parallel to the Edge of the End of the
Mortise), and also thro’ the Hole _f_ in _Fig._ 3. in _Plate_ 2. which
is seen in its Place at A in _Fig._ 3. _Plate_ 3. and likewise through
both Sides of the Mortise near their upper Edges, and as near the
Fore-end of the Mortise as may be, without the Tongue’s rubbing against
the said Fore-end.
The Breadth of the Tongue must be conformed to the Breadth and Bevel
of the Mortise, and when it is on its Axis, it being raised tight up
as far as the short prick’d Line _l m_ in _Fig._ 3. _Plate_ 2. being
One-eighth Part of the great Hole, and being there, you see its upper
Edges touch both Sides of the Mortise by their whole Length: Then it is
rightly made: and by this touching both Sides of the Mortise tightly
and closely, when raised up to that Degree, it appears, that the Two
upper Edges of the Sides of the Tongue are inclined to each other in
an Angle that is more acute, by about One-third, than is the Angle of
Inclination of the Sides of the Mortise.
Hence, when the Tongue is let down to its Place, there will be on each
Side of it an empty Space, betwixt it and the Mortise, of the Form of
a very acute Triangle, whose vertical Angle is more or less acute,
according as the Tongue approaches nearer to, or recedes farther from
the Spindle.
This _Fig._ 1. _Plate_ 3. is the brass Tongue with its Back-side
upwards. The Two outer Lines _a b_ and _c d_ are the Edges of the upper
Surface (tho’ turned downwards in this Figure), which are inclined to
each other, as afore-mentioned; but the Two inner Lines _e f_ and _g h_
are nearer to each other, whereby this under Surface is narrower than
the upper: Both must be plain Surfaces, but the upper and its Two Edges
very free from Flaws, and smooth, or polished.
The Reason why the under Surface is narrower than the upper, is to
preserve the Bevel of the empty Triangle: For though the Bevel of the
Sides of the Mortise would be sufficient for this, if both Sides of the
Tongue were sure to keep equally distant from the Spindle; yet as the
Tongue never is so tight on its Axis, but that sometimes one Corner of
it may be nearer to the Spindle than the other, in this Case, that Side
which is nearest to the Spindle would reverse that Bevel, so as to make
the small empty Space that is betwixt the Mortise and the Tongue, wider
above than underneath.
C C are the Two little Knobs that prevent the Spring from slipping to
either Side, and are at the Distance from one another of the Breadth of
the Spring.
_Fig._ 2. shews one Side, and the Thickness of the Tongue the other
Side, being the same. _a b_ shews the polished Surface (being a true
Plane), whereon the Seed runs down to the Spindle. _c d_ the Back-side,
which lies turned uppermost in _Fig._ 1. _b e d_ shews one End of the
hollow Cylinder of the Tongue, thro’ which its Axis passes.
The Length of the Tongue must be such, as will reach lower than just
to touch the Bottom of the great Hole as a Tangent: for, if it be
not longer than that, it might happen, that when the Mortise is empty
of Seed, and the Tongue set up close, a Wheel might, in Turning, or
otherwise, go a little backwards, and cause a Notch of the Spindle to
take hold of the End of the Tongue, and tear it out of the Mortise:
Therefore let the Tongue reach a little below the Spindle, as the
pricked Line _g h_, in _Fig._ 3. of _Plate_ 2. doth.
As for the Posture in which the Tongue ought to stand in the Mortise,
it is shewn by the Three pricked Lines in _Fig._ 3. _Plate_ 2. where
the pricked Line _g h_ makes an Angle of Forty-five Degrees, being the
nearest that it can stand to the Spindle; the pricked Line _i h_ makes
a somewhat greater Angle, and it is a mean (or middle) Distance from
the Spindle; and the pricked Line _k h_ is supposed to be its greatest
Distance, where the Tongue makes its greatest Angle with the Top and
Bottom of the Mortise. If the Tongue stood so obliquely as to make
an Angle much less than Forty-Five, the Tongue would rise too much
against the Bevel of the Mortise, and the Spring would have the greater
Difficulty in returning it to its Place, when driven back by the Force
of the Notches.
And beside, when the Tongue stood wide from the Spindle, there might be
so much Room betwixt it and the Sides of the Mortise, that some Seeds
might fall thro’ there.
The Steel Spring is D, properly placed upon the Back of the Tongue, in
_Fig._ 1. _Plate_ 3.
At first, I made the Spring double, _i. e._ with Two Legs, in Imitation
of that in the Organ, and fastened into its Tongue, much after the same
manner as the Spring of the Organ is into its Tongue or Flap, which
prevents the compressed Air from passing out of the Sound-board, except
whilst the Key is thrust down by the Finger of the Player; but the
Drill-spring requiring to be of a vastly greater Strength than that,
I made it of Steel, of the Breadth of half an Inch, instead of Brass
Wire: This performed very well, and several Drills are yet extant, that
have only this Sort of Springs: Yet I found there was great Difficulty
to set the Legs at their due Distance from each other; for their
Seasoning would alter them from what they were, whilst the Steel was
soft: They also took up too much Room in the upper Part of the Mortise.
Then, to remedy these Inconveniencies, I made it single, with only
one Leg, which by full Experience is found to be much better than the
double one; it does not contain a Fourth Part of the Metal, and is most
easily made, requiring none of that Trouble and Nicety that the double
Spring doth. I shall therefore give a Description of the single Spring
only.
B, the End of the Screw, which holds the Spring to the Tongue, thro’ a
Hole near the upper End of the Spring; D, the Middle, against which the
End of the Setting-screw bears.
Its Length is almost the whole Length of the Tongue; the End E reaching
very near to the lower End of the Tongue, and the End B is as near
the upper End of the Tongue; as it can be placed without touching the
Cylinder of the Tongue.
The Breadth is usually about half an Inch; the Thickness must be in
proportion to its other Dimensions, and according to the Degree of
Stiffness required.
The longer it is, the thicker it must be, to have the same Stiffness;
but the broader it is, the thinner it must be of the same Length; so
that it is hard to determine its Thickness. It is made stiffer or
stronger by being cut shorter; it is made weaker, or less stiff, by
filing or grinding it either thinner or narrower.
The common Thickness is about that of a Shilling[262].
[262] Not quite so thick as a milled Shilling, but rather of an old
broad stamped Shilling, which is a little thinner.
The Degrees of Stiffness are measured in this manner; _viz._ Fix Two
Boards together, leaving a Chink betwixt them, in one Place of an Inch
long; lay the Spring (when seasoned across this Chink) with its Middle
exactly over it; then put a String over the Spring, which may pass
with both Ends thro’ the Chink, and tie so much Weight to the Ends of
the String under the Boards, that will pull down the Middle of the
Spring, till it touch the Chink, and is strait with both its Ends; This
will shew the Degree of Stiffness. But note, That the Spring must be
crooked, and bear only upon its Ends, with the hollow Side upwards.
If ten or a dozen Pounds Weight pull it down to the Board, it is a good
Degree of Stiffness, for a large Box: We are not confined to be very
nice or exact in the Degree of Stiffness; for by our Fingers pressing
it, we that are practised in it, know well enough, whether a Spring be
of a sufficient Degree of Stiffness, without weighing it; but for such
who are unacquainted with them, it is best not to trust to Guess, but
Weights; and to adjust the Stiffness to that of a Spring, that has been
known to perform well.
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.
If ever there shall be Occasion for this Sort of Notches, it must be
when a great Proportion of Seed is to be drill’d by a small Spindle,
and low Wheels: The Smalness of the Spindle may not, by a single Set,
admit of a sufficient Number of Notches (of a proper Bigness) in its
Circumference; not that a double Set, by its double Number, will
throw down a greater Quantity of Seed than a single Set of the same
Width and Depth, but a less Quantity; But it may be feared, that a
very small Number of Notches might not spread the Seed so much as to
cause it to lie even in the Chanels, one Notchful falling all to the
Ground, before any of the next Notchful reaches it, which would make
Chasms or Gaps in the Row of Corn or Legumes: This, such a double
Number of Notches will certainly prevent.
It would seem, that the higher the Wheels, the more need there should
be for this double Set of Notches: But it appears to be otherwise;
for the greater Distance the Seed has to fall, the more it spreads,
and strikes oftener against the Funnel and Trunk; and by that means a
Notch from high Wheels will, with the same Quantity of Seed, supply a
greater Length of the Chanel (or Furrow) than a Notch will from low
Wheels.
In all my Practice I never had any Occasion for such a double Set of
Notches, either with high or low Wheels, or even when I drilled into
open Chanels, without Funnels or Trunks to my Drill-plough; and yet
my Rows of St. Foin, and of Corn, were always free from Gaps, being
equally supply’d with Seed from one End to the other.
If ever there is Occasion for more than a single Set, it must be for
Beans, for which also I think a large Spindle is better than a double
Set of Notches in a small one. The largest Spindle I have known made,
is of Two Inches and an half Diameter, and that only for Horse-Beans.
The best Sort of Notches for a double Set are those which have convex
Bottoms; because such are less liable to drop their Seeds without the
turning of the Wheels, than any other Sort: And a double Set must
be in greater Danger of this, as the Tongue is always hindered from
pressing so closely against any Notch, being held open by the Seeds
on the opposite Interstice; which is contrary to a single Set, where
no Seed can lodge at either End of a Notch, to hold open the Tongue,
or hinder its pressing against it.
_Note_, When I made my Boxes of Wood, I had double Boxes, with a
Partition between such a double Set of Notches; but never made such
in Brass, not knowing whether that Partition, by its Thinness of hard
Metal, might not cut the Spindle: Yet I never found any Occasion for
a double Row of Notches. I made those double Boxes only for drilling
Two Sorts of Seeds at once into the same Chanel.
The other Way of varying the Proportion of Seed in the same Boxes, is
by the Diameter of the Wheels, when we can alter them; for Wheels, of
what Diameter soever they are, must turn round all the Notches at one
Revolution; so that Wheels of Twenty Inches Diameter will deliver out
a third Part more Seed than Wheels of Thirty Inches Diameter, into the
same Length of the Chanels; but we seldom have any Occasion to alter
the Wheels, unless it be on account of planting a Species of Seed of
a different Magnitude, as the largest Sort of Peas, and small-grain’d
Wheat, or St. Foin Seed are.
These are all the Ways we have to alter the Proportion of Seed, we
drill with the same Seed-boxes; these Two Sizes, already described,
being sufficient for all Sorts of Corn and Seeds which we commonly sow,
from Marrow-peas to Turnep-seed; but, for drilling of Beans, the Boxes
must be larger, and are commonly made of Wood, the Spindle Two Inches
Diameter, or more, and the Boxes Two Inches wide: Where note, That this
Increasing of the Width of the Mortise, from an Inch and an half, to
Two Inches, increases the Quantity of Seed to almost double; because
this Half Inch is all added to the Middle of the Notches, where they
are deeper than their Ends; the Bevel of which takes up a considerable
Part of the Length of the Notches. For Beans, they also contrive to
have their Wheels as low as conveniently they can. These Wooden Drills
are now become common in many Places.
The Wooden and Brass Seed-boxes differ not in any of the most essential
Parts of them; only the Wooden Box must be thicker, as the Wood is not
so strong as Brass; the Spring is made strait instead of crooked; and,
being let into the Back of the Wooden Tongue, bears against it at each
End; and the Chanel, into which it is placed, being made hollow in the
Middle, the Spring has its Play there, and must be stiffer and have a
little more Play in the Bean-drill, than in any lesser Seed-box.
I, at first, made all my Seed-boxes of dry Box-tree Wood, which
performed very well, and are still used: But, a few Years ago, a
Gentleman advised me to make them in Brass; the doing of which has put
me to a great deal of Trouble and Expence, for want of understanding
the Founder’s Art: Yet this I do not repent, because they are, in some
respect, better than those made in Wood; especially to those who do not
well understand their Fabric; for, to such, the Swelling and Shrinking
of the Wood was inconvenient in small Boxes: And I now am told, that
they are cast in _London_ of the best Brass, at the Price of One
Shilling _per_ Pound, and so smooth as to require very little filing.
And these Brass Boxes being also more lasting than Wood, and not much
more expensive, when Workmen know how to make them, I think it not
worth while to give any particular Directions for making them in Wood.
As to the Spindles of the Turnep-boxes, I have often made them with a
mix’d Metal, of half Pewter, and half Spelter, which perform very well,
and are easily made; because this Metal will melt, almost as soon as
Lead, in a Fire-shovel, to be cast in a Mould; but Brass will not melt
without a Crucible.
The first Idea that I form’d of this Machine, was thus: I imagin’d the
Mortise, or Groove, brought from the Sound-board of an Organ, together
with the Tongue and Spring, all of them much alter’d; the Mortise
having an Hole therein, and put on upon one of the Iron Gudgeons of
the Wheelbarrow; which Gudgeon being enlarg’d to an Inch and an half
Diameter, having on it the Notches of the Cylinder of a Cyder-mill, on
that Part of it which should be within the Mortise, and this Mortise
made in the Ear of the Wheelbarrow (thro’ which the Gudgeon usually
passes), made broad enough for the Purpose; this I hoped, for any thing
I saw to the contrary, might perform this Work of Drilling; and herein
I was not deceived.
As for placing a Box over this Mortise to carry a sufficient Quantity
of Seed, it was a thing so obvious, that it occasion’d very little
Thought; and an Instrument for making the Chanels, not much more;
neither for applying Two Wheels, one at each End of the Axis, instead
of the single Wheel in the Middle of the Axis of the Wheelbarrow.
At first my Plough made open Chanels, and was very rude, being composed
of Four rough Pieces of Planks, of little Value, held together by Three
Shoots, or Pieces of Wood, which held them at a Foot Distance one from
the other; These Pieces, being cut sharp at Bottom, made the Chanels
tolerably well in fine Ground. But I soon contrived a Plough with Four
Iron Shares, to make Chanels in any Ground: This drew a Hopper after
it, having Four Seed-boxes at its Bottom, carried on a Spindle by Two
low Wheels, which had Liberty to rise and sink by the Clods that they
pass’d over: The Seed-boxes delivered their Seed immediately into the
open Chanels.
[Illustration: _Plate. 3_
_P. 344_
_W Thorpe sculp._]
This Plough and Hopper were drawn by an Horse, and the Seed, lying
open in the Chanels, was covered sometimes by a very light Harrow, and
sometimes by an Hurdle stuck with Bushes underneath it.
I soon improv’d this Plough to perform better, and to make Six Chanels
at once, and sometimes a great many more.
This Plough and Hopper, with their Improvements and Alterations, are
shewn in _Plates_ 4. and 5.