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.