Page:Popular Science Monthly Volume 90.djvu/476

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��Popular Science Monthly

��How to Plot Angles Accurately in Fractional Parts of a Degree

THE following is a simple and accurate method of plotting angles, especially where they are to be inter- preted in fractional parts of degrees

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��A method of plotting angles where they are interpreted in fractional parts of a degree

which would be difficult to read from or- dinary protractors.

As an example let it be required to lay off an angle of 29°— 21'— 28". By consulting a table of natural tangents we find the tangent of the given angle to be .5625, and as this represents the altitude of a right angle triangle whose base is unity, it is quite evident that, if we lay off a base line 10 in. long, the altitude will be ID ins. x .5625, or 5.625 ins., as in Fig. I.

Again, suppose it is required to determine the angle b, in Fig. 2.

Lay off on — x, or — x produced, — /, equal to 10 in. and from / erect a perpendicular / — 5 of any convenient length. Extend — y, if necessary to intersect / — 5 at u.

For reasons previously explained, t — u is ten times the natural tangent of angle b. Therefore, if t — u is measured and found to be 4.78 in., the tangent of b will naturally be 4.78-Mo, or .478 = 25° — 33'. — Harry B. Wrigley.

��Bracing the Back of a Long File for Level Work

THE drawing shows a method of trussing a long file so as to make the teeth on the cutting face more effective, and also to produce a slightly

���A truss rod placed on a long file to brace it and make the cutting more effective

convex surface, enabling the file to be used for broad work without rounding.

��A block is placed near the center of the file, over which a 3<^-in. or ^/le-in. rod passes. This has a hook to engage the file at the forward end, and passes through a hole drilled in the handle, where a nut is run on the threaded end. By tightening this nut the file may be sprung slightly convex, increasing its usefulness for certain classes of work.

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��Holding Reference Drawings on a Drawing Board Conveniently

T is quite necessary to have on the

��drawing board at times a bound bunch of blue prints for reference and they cannot be kept in place very well on a slanting surface. To facilitate their easy handling and hold them. in place the arrangement shown was constructed.

It consists of a wood cylinder A about I >^ in. in diameter and about 24 in. long,

���Clamp arrangement to hold a bundle of reference blue prints on a drawing board

supported by two ^-in. bent rods which are fastened to the bar B, the latter being supported by two brackets C fastened to the bottom side of the drawing board.

A rod D is fastened to the bar B and extended to a convenient point at the front of the drawing board. The rod D is held in position by the hook E, which is double, the same as the brackets C. To release the drawings unhook rod D and move it downward. The rod D can be bent so that when it is in the hook it will bring the proper pressure on the cylinder A to hold the drawings in position on the board.

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