WORKING IT OUT ON PAPER
The next step after, and sometimes even before, you have thought out
your great idea is to make a drawing of the invention it represents.
Nearly every one can do a little _free hand drawing_ and this is a
good way to make rough sketches to aid the mind in further developing
thought.
But if you can make a simple _working drawing_ of your device, that
is a picture in which all of the parts are drawn in proportion, or to
_scale_ as it is called, the whole thing will stand out clearly before
you and you can see where it is wrong and make the needed changes on
paper before you try to build a model.
[Illustration: FIG. 13. A TWELVE INCH RULE]
[Illustration: FIG. 14. A PAIR OF CHEAP COMPASSES]
~Tools for Making Simple Drawings.--~To make simple working drawings,
or _mechanical drawings_ as they are called, all the tools you need are
a good, straight 12-inch rule, as shown in Fig. 13, _compasses_ as
shown in Fig. 14, a medium hard lead pencil, a rubber eraser and some
smooth white paper.
~How to Make Simple Working Drawings.--~At A in Fig. 15 is shown a
drawing in perspective, that is as it would look to the eye, of a
_rectangular_ box, while B is a top view, C is a side view and D is an
end view of the same box; of course the bottom and the other end and
side cannot be seen but you can imagine pretty well that they are there
if you try to.
[Illustration: FIG. 15A. AN ISOMETRIC PERSPECTIVE DRAWING OF A BOX]
[Illustration: FIG. 15. B, A TOP PLAN VIEW OF THE BOX. C, A SIDE PLAN
VIEW OF THE BOX. D, AN END PLAN VIEW OF THE BOX]
To show the top, bottom, sides and ends of a box, or other device, you
don’t need to draw out the whole thing in perspective but you can make
a flat, or plan view of each part as shown at B, C and D in Fig. 15,
that is an outline drawing shown as though you were looking squarely at
it in the center and with the measurements marked upon it.
If now you will make a set of these working drawings of, say, a box
and draw each part to _scale_, that is measured off in proportion, as
shown in B, C and D, and saw out of a board the top, bottom, sides and
ends and nail them together you will have a box like that shown in
perspective at A.
[Illustration: FIG. 15. E, A CROSS SECTION VIEW OF THE BOX. F, DETAILED
DRAWING OF THE HOOK]
Plan views are easy to draw because they are formed of horizontal and
vertical lines, and wheels are shown as true circles. After making your
plan views, though, the safest way is to make a perspective drawing to
the same scale for when you are looking at a square object as it really
is it always appears larger than the plan views would indicate. But
this is ahead of the story.
Now suppose you wanted to show how the box would look if it was sawed
lengthwise through the middle. You simply make a _cross-section_ view
of it as shown at E and any one who knows how to read drawings will
understand it. To show the hook on the front of the box more clearly it
can be drawn separately as at F and this is called a _detail drawing_.
Exactly in the same way any device, apparatus or machine can be shown
by top, side and end views and by _cross-section_ and detail drawings.
[Illustration: FIG. 16. A SIDE VIEW OF A STEAM ENGINE]
Just to see how something a little more complicated would work out on
paper, let’s take the cylinder and steam chest of a steam engine. First
draw a side view of these parts as shown in Fig. 16.
As the steam chest is a rectangle and every side of it is flat it can
be shaded by drawing fine parallel lines spaced equally apart. The
cylinder, pipes and rods are round, or rather cylindrical, and to get
this effect these parts should be shaded with parallel lines drawn
close together beginning at the top and bottom and making them ever
farther apart as you get toward the middle and this will give it a
rounded appearance.
Next draw the end view of the cylinder and steam-chest. Since the
cylinder has been given a diameter of 3¼ inches in the side view, of
course it must have the same diameter in the end view as shown in Fig.
17.
[Illustration: FIG. 17. AN END VIEW OF A STEAM ENGINE]
By looking again at Fig. 16 you will see that the steam chest is 4½
inches long and that it is 2½ inches high but it is in the end view
Fig. 17, that the width of it is shown. The end of the steam chest is
shaded with straight parallel evenly spaced lines and the cylinder
head is shaded with _concentric circles_, that is with circles equally
spaced apart and having the same center.
[Illustration: FIG. 18. A TOP VIEW OF A STEAM ENGINE]
In this and many other cases a side view and an end view give all the
outside dimensions needed but sometimes a top view must also be made,
and this is shown in Fig. 18.
[Illustration: FIG. 19. A CROSS-SECTION OF A STEAM ENGINE]
While all of these views show the outside of the steam chest and the
cylinder they give no hint as to how the inside is made. Suppose you
had invented the steam engine of course you would know how the inside
should be made and so you make a cross-sectional drawing of the parts
as shown at Fig. 19, and then the construction and even the operation
of the engine looms up as though you had turned a searchlight on it.
[Illustration: FIG. 20. THE SIDE VALVE SHOWN IN DETAIL]
That is all of it will be clear except perhaps the slide valve and this
is where a detailed drawing comes in to show a small part, or a part
that is hard to understand by looking at the side, end and top views.
The slide valve, see Fig. 20, is drawn in detail and the picture is
made large and bold. The slide valve is made of a cast piece of metal
hollowed out. It and the completed steam chest and cylinder are both
drawn in _perspective_, that is just as the eye would see them if they
were actually made of metal. The latter is shown in Fig. 21.
[Illustration: FIG. 21. AN ISOMETRIC PERSPECTIVE DRAWING OF A STEAM
ENGINE]
~A Simple Way to Draw in Perspective.--~Did I hear you ask how you can
make a drawing in perspective? List and I will tell you the simplest
way--a way so that you do it the first time you try.
Buy a quire of _isometric_ (pronounced i-so-met´ric) _cross-section
paper_ 6 by 9 inches, at a cost of 15 cents, of any dealer in
drawing materials. This paper is lined in faint colored ink in three
directions, as shown in Fig. 22, and which represent length, breadth
and thickness.
[Illustration: FIG. 22. A SHEET OF ISOMETRIC DRAWING PAPER. THE REAL
SHEETS ARE PRINTED IN NEUTRAL TINTS, THAT IS, COLORS WHICH DO NOT
INTERFERE WITH THE DRAWING]
Now _isometric_ comes from _iso_ which means _equal_ and _metric_ which
means _measure_, so isometric means _equal measure_ and the three lines
used in isometric perspective are at equal distances from each other.
The lines which cross the vertical lines on isometric cross-section
paper are 30 degrees from the base, or horizontal line and the vertical
line is, of course, 90 degrees from the horizontal as shown in Fig.
23. Having everything at hand suppose you try to draw a square frame.
Begin by making the first upright and you will see by looking at Fig.
23 that all you have to do is to draw three vertical lines and join
the top and bottom by marking over the 30 degree lines. This done draw
three more uprights in the same way and when you have these on paper it
is easy to put beams on top or struts between them as shown at Fig. 24.
[Illustration: FIG. 23. FIRST STEP IN ISOMETRIC PERSPECTIVE DRAWING]
As all the lines are of equal measure you can mark on the exact
dimensions as shown in many of the isometric perspective drawings in
this book. For a drawing of some device, or of a whole machine, to
give to some mechanic to make for you the better way is to hand him a
perspective drawing together with the top, side and end views, rather
than the latter views alone, and then he will not need to figure out
how they are put together.
[Illustration: FIG. 24. THE NEXT STEP IN ISOMETRIC PERSPECTIVE DRAWING]
To show to a better advantage how isometric perspective works out look
at Fig. 25 and you will see how the bearings of a crankshaft of a four
cylinder gas engine stand out in a vertical line, up and down and in
a horizontal line right and left as though they were real and made in
three dimensions.
[Illustration: FIG. 25. A CRANK SHAFT DRAWN ON ISOMETRIC PAPER]
~How to Make Isometric Paper.--~To make isometric perspective drawings
you can get along without the cross-section paper described above
though this is the easiest and most accurate way to get results.
But you can make these drawings on any kind of paper if you know how to
use a _protractor_ and measure of 30 degrees. To do it right you should
have some drawing tools and if you are an inventor you should have them
anyway.
~Drawing Tools You Need.--~For making drawings of any kind you should
by all means have a _drawing-board_ as shown at A in Fig. 26. As a
drawing board must be perfectly square and made so that it cannot warp
it is better to buy one of a dealer in drawing materials.
[Illustration: FIG. 26A. A DRAWING BOARD]
A good board is built up of thoroughly seasoned strips of white pine
glued together and fitted with end ledges; a small board say 12 by 17
inches on the sides can be bought for 50 cents or a little more and it
will serve you well. A 12 inch _triangular boxwood architect’s scale_
is shown at B in Fig. 26 and is much handier to use than a common rule.
[Illustration: FIG. 26B. A TRIANGULAR SCALE]
A beginner’s set of drawing instruments consisting of _compasses_, with
pen and pencil points, a _ruling_ pen and a box of leads all in a nice
pocket case, as shown at C, Fig. 26, can be bought for $1.25 and these
compasses are easier to handle than the one shown in Fig. 14.
[Illustration: FIG. 26C. A SET OF INEXPENSIVE DRAWING INSTRUMENTS]
But the chief instrument you need is a _protractor_, as shown at D,
Fig. 26. This is a _semicircle_ of brass, or of German silver, 3¾ or
4½ inches in diameter and costs 10 cents or 40 cents, according to the
size and metal it is made of.
[Illustration: FIG. 26D. A PROTRACTOR FOR MEASURING CIRCLES AND ANGLES
BY DEGREES]
A protractor, as you may or may not know, is used to lay off _angles_
and to measure _angles_ in _degrees_. The curved part or scale of the
protractor is divided into 180 degrees since there are 360 degrees in
a circle. The figures start at both corners with 0 so that an angle of
any number of degrees right or left can be marked off. Now the lines
formed by marking off angles of 30 degrees are the only ones you will
have to make for isometric perspective. To do this fasten a sheet of
paper to your drawing board with thumb tacks at each corner and draw
a straight line across the paper near the bottom. Put your protractor
on the edge of the paper and the pencil line exactly as shown in Fig.
27; lay your rule so that its edge crosses the straight part of the
protractor at the middle, marked A in the drawing and also on the line
of the scale of the protractor marked 30 degrees and then draw a line
on the paper along the edge of your rule.
[Illustration: FIG. 27. THE POSITION OF THE PROTRACTOR ON PAPER]
This done place the protractor on the opposite and left hand edge of
the paper and the horizontal line and lay your rule with its edge
crossing the middle of the straight part of the protractor as before
and on the 30 degree line of the scale and so that when you draw the
line it will cross the other 30 degree line as shown in Fig. 27.
If now you draw another line at 90 degrees, that is vertically, between
the two crossed lines, also as shown in Fig. 27, each of the three
lines will be exactly the same distance apart in degrees. You can go
ahead now and draw lines ⅛ inch apart parallel with each of the three
lines and you will have a sheet of isometric cross section paper of
your own making.
~How to Draw Isometric Ellipses.--~_An Easy, Rough Way._--There is
just one more little thing you should know about making isometric
perspectives and that is how to draw disks, wheels and anything else
that is circular in form so that they will look right and be right.
[Illustration: FIG. 28A. THE PROPORTION OF AN ISOMETRIC ELLIPSE]
In isometric perspective everything that is round in reality is drawn
in the shape of an _ellipse_, that is a closed curve that is longer
than it is wide as shown at A in Fig. 28; there are different shaped
ellipses but there is only one used for isometric drawing and this is
always in the ratio of 1¼ to 2; that is if an ellipse is 2 inches long
it will be 1¼ inches wide; an ellipse 4 inches long will be 2½ inches
wide and so on.
An easy, though rough way to draw an isometric ellipse is to make
a line as long as the diameter of the disk or wheel you intend to
represent; draw another line which is the width of the ellipse through
the center and at right angles across it, see A again and then draw the
curved line around the end of them free hand.
[Illustration: FIG. 28B. HOW ELLIPSES STAND OUT IN RELIEF]
How these ellipses are made to appear as if they were set either in a
vertical or a horizontal position and at right angles to each other is
shown at B in Fig. 28. The _axis_, that is the spindle, or shaft on
which the disk, or wheel, is mounted, must always follow the 30 degree
line running at right angles to the edge of the board or whatever it
is supposed to be fastened to or goes through; and the thickness of the
disk or wheel is always shown on the same sides as the thickness of the
board or other part on which it is mounted, all of which is brought out
clearly at B in Fig. 28.
~How to Draw an Isometric Ellipse.--~_A Harder but More Accurate
Way._--Begin by drawing a straight line as long as you want the longest
axis of your ellipse to be, as shown at A B, Fig. 29. Divide this line
into four equal parts. Now take your compasses and with the needle at
the center of the line O draw a circle having the line as its diameter.
[Illustration: FIG. 29. HOW AN ISOMETRIC ELLIPSE IS DRAWN]
Next start at A with your dividers and divide the whole circle into ten
equal parts and then take your rule and draw a line from the point C on
the circle through the point G on the diameter and _produce_, or extend
it to the bottom of the circle; draw a line from D through G and extend
it to the top of the circle; draw a line from E through H and extend
it to the bottom of the circle when it will intersect the line C G at
the point J; and finally draw a line from F through H to the top of the
circle which will intersect the line D G at I.
Take your compasses and using G as a center draw the arc K A L; then
using H as a center draw the opposite arc M B N; using the point J as a
center, draw the arc K M so that its ends will meet the upper ones of
the end arcs perfectly; using the point I as a center draw the fourth
and last arc L N when the ellipse is completed.
When making isometric ellipses much care must be taken to make all
the points and draw all the lines with the greatest accuracy as the
slightest error will distort the whole thing.
~How to Shade Drawings.--~Besides the few hints for shading perspective
drawings which I have given above there are certain ways to shade
cross-sections and elevations to show whether it is made of metal,
glass, wood, liquid, cork, carbon, insulation or other materials. There
are also different kinds of shading to show fine and coarse fabrics and
the various colors.
[Illustration: FIG. 30. A SHADING AND LETTERING CHART FOR DRAWINGS]
The patent office has prepared a chart showing the shading that should
be used to represent the different materials and colors and these are
reproduced in Fig. 30. The letters of the alphabet both _upper_ and
_lower case_, as the capitals and little letters are called, which
are used by mechanical draftsmen are also shown in Fig. 30. As these
letters and figures are clear, easy to make and are preferred by the
patent office they are good ones for you to use.
~How to Make Electrical Symbols.--~In making drawings, either for
yourself or for the patent office, of electrical apparatus to show
how it is connected up you do not need to draw out a plan view or a
perspective of each part but you can make what are called _symbols_.
Symbols are simply a few lines or signs that stand for or represent
a certain piece of apparatus; as an illustration suppose you want to
show a dry cell, all you need to do is to make a couple of parallel
lines, one shorter and heavier than the other like this:
[Illustration: cell]
and if you want to show a battery you make as many pairs of parallel
lines as there are cells in this fashion:
[Illustration: battery]
And just so with every separate piece of electrical apparatus, and all
of them are shown at A and B in Fig. 31.
[Illustration: FIG. 31A. A CHART OF ELECTRICAL SYMBOLS]
[Illustration: FIG. 31B. A CHART OF ELECTRICAL SYMBOLS]
~How to Read Electrical Diagrams.--~From the plates of symbols given
at A and B in Fig. 31, you will see that the symbol for a battery is
a pair of parallel lines as shown above, that the symbol for a motor
is made in this fashion:
[Illustration: motor]
and that a switch is made like this:
[Illustration: switch]
now if you want to show a battery, a motor and a switch wired
together all you have to do is to join the symbols with lines as shown
at C in Fig. 31 and you will have what is called a diagram.
You can _read_ a diagram, that is understand how it is connected up, in
an instant for you can see at a glance how the wires run. Because the
wiring is shown so simply and clearly diagrams of this kind are usually
called _wiring diagrams_.
[Illustration: FIG. 31C. A SIMPLE WIRING DIAGRAM]
In drawing wiring diagrams try to place each symbol in such a position
that the connecting lines which represent the wires cross each other as
seldom as possible, otherwise your diagram will be confused and it will
be hard to follow out the circuits.
~Some Aids to Drawing.--~The following aid to drawing and designing was
published in the _English Mechanic_ and you will find it very helpful
if your invention has to do with an automobile, aeroplane, or any large
machine which is used or actuated by a person.
[Illustration: FIG. 32A. THE DIMENSIONS OF A MANIKIN]
Make a manikin, that is a little jointed figure of a man as shown at A
in Fig. 32. The figure can be made to any scale but 1 inch to the foot
which is ⅙ full size is a good ratio to make it but it must of course
be made to the same scale as the machine you are drawing.
To get the right proportions rule a sheet of paper a couple of inches
wide and about 8 inches long so that the divisions will be ¹/₁₂ inch
square and draw on this the different parts of the manikin as shown at
B in Fig. 32. Now since every ¹/₁₂ inch on the paper is equal to 1 inch
for a man 6 feet tall your manikin will be 6 inches high when it is
jointed and complete.
[Illustration: FIG. 32B. THE PROPORTIONS OF A MANIKIN DRAWN ON
CROSS-SECTION PAPER]
The figure can be made of cardboard if it is to be used only a few
times but thin wood, celluloid or hard rubber, or sheet tin, brass or
copper will make a much more substantial one. Whatever the material
that is used the edges of each part should be filed smooth; and when
you rivet the parts together to make the joints the latter should work
smooth and yet stiff enough so that the parts will stay in whatever
position you place them.
[Illustration: FIG. 32C. A TRIAL POSITION OF THE MANIKIN]
When you lay the manikin on your drawing you can see whether or not the
levers are in the right places as shown at C and D in Fig. 32.
[Illustration: FIG. 32D. ANOTHER TRIAL POSITION OF THE MANIKIN]
~Making Cardboard Models.--~In drawing out your invention you will
often find that you can’t get the image you have in your mind’s eye
down on paper.
There may be the movement of a lever, the turning of a wheel or the
motion of a cam that you cannot quite see through and try as you will
to work it out on paper the thing refuses to materialize. Under such
conditions it would be a great waste of time and money to set about
building a real model but there is an easy way out of the difficulty
and that is to make a cardboard model of the device.
Just as an illustration take the case of an aeroplane. Say that your
big idea is a scheme for controlling the _elevating planes_ and the
_direction rudder_; you have clearly in mind the use of an elevating
plane on each side of the rudder and yet when you try to draw it out
these two parts won’t fit together at all as you expected them to do.
When you reach this point get a sheet of heavy cardboard, shears,
bottle of liquid glue, pins, matches or toothpicks, some thin wire, a
few corks and a sharp knife.
Out of these materials you can build up the _fuselage_, as the body of
the aeroplane is called; next you can fasten on the rudder and then the
elevation planes; and when you have the tail-planes put together with
real materials and actual shapes and sizes they will stand out in bold
relief and you will have no trouble in making your drawings from the
cardboard model.
Or suppose you have an idea for a gyro-motor such as are used for
driving aeroplanes. Now in this motor the shaft to which the pistons
are fastened stands still and the cylinders in which the pistons move
revolve. It is rather a curious motion and not easy for a fellow who is
not posted on mechanics to grasp offhand.
What’s the thing to do? Why, make a cardboard model of the mechanism
using pins for the shafts and you will have a model that will look like
Fig. 33, and when you turn the cardboard disk with the cylinders marked
on it you will see at once exactly how the motor works.
[Illustration: FIG. 33. A CARDBOARD MODEL OF A GYRO ENGINE]
And so it is with many other contrivances; when you come to any part
that doesn’t seem to fit or is not clear, make a cardboard model and
your troubles will vanish as dew-drops in the morning’s sun.