Technical Drawing Tools

Technical drawing tools are the tools used for technical drawing, including pens and rulers. Drawing tools may be used for measurement and layout of drawings, or to improve the consistency and speed of creation of standard drawing elements. Many of the tools used for manual technical drawing are obsolescent, where computer-aided drawing has become common.

• Drawing Tools

• Pens

Traditional and typical pens used for technical drawing are pencils and technical pens.

Pencils in use are usually mechanical pencils with a standard lead thickness. General line widths are 0.18 mm, 0.25 mm, 0.5 mm and 0.7 mm. Hardness varies usually from HB to 2H. Softer lead gives a better contrast, but harder lead gives more accurate track. Bad contrast of the lead track in general is problematic at photocopying, but new scanning copy techniques have improved the final result. Paper or plastic surfaces do require their own lead types.

"Drawing pens"

Traditional already in the 1600s used ruling pen.   Grafos-stylus.   A disassembled Grafos and nibs of different widths.   Rapidograf styluses of different widths: 0.35, 0.5 and 0.7 mm.   Rapido graph stylus parts. The head is possible to disassemble to even smaller parts

In most cases, the final drawings are drawn with ink, on either plastic or tracing paper. The pen is generally Rapido graph-type technical pen, a marker pen that draws lines of consistent width (so-called steel marker pen). The pen has an ink container which contains a metal tube, inside which is a thin metal needle or wire, the soul. Ink is absorbed between the needle and the tube wall, preventing an excessive amount of ink from being released. The needle has a weight and by waving the pen back and forth the needle is released and the ink can run. Previously, the tank was filled from an ink bottle, newer styluses use ink cartridges.

Each line width has its own stylus. Width of the line is standardized: In Finland, the most commonly used set is 0.13 mm, 0.18 mm, 0.25 mm, 0.35 mm, 0.50 mm and 0.70 mm. There are their own style for tracing paper and plastic, because plastic requires a harder pen tip. To function well they require regular maintenance, the finest marker pens in particular

• Drawing Board

The drawing board is an essential tool. Paper will be attached and kept straight and still, so that the drawing can be done with accuracy. Generally, different kind of assistance rulers are used in drawing. The drawing board is usually mounted to a floor pedestal in which the board turns to a different position, and also its height can be adjustable. Smaller drawing boards are produced for table-top use. In the 18th and 19th centuries, drawing paper was dampened and then its edges glued to the drawing board. After drying the paper would be flat and smooth. The completed drawing was cut free. Paper could also be secured to the drawing board with pins. More recent practice is to use self-adhesive tape to secure paper to the board. Some drawing boards are magnetized, allowing paper to be held down by long steel strips. Boards used for overlay drafting or animation may include registration pins or peg bars to ensure alignment of multiple layers of drawing media.

• Drafting Machine

A drafting machine is a device which is mounted to the drawing board. It has rulers whose angles can be precisely adjusted with a controlling mechanism. There are two main types of apparatus: an arm-type parallelogram apparatus based on a hinged arm; and a track-type apparatus which moves on a rail mounted to the top of the drawing board. The accuracy of the arm type apparatus is better in the middle of the board, decreasing towards the edges, whereas a track machine has a constant accuracy over the whole board. The drawing head of a track-type drafting machine slides on bearings in a vertical rail, which in turn is moved along a horizontal, top-mounted rail. Both apparatus types have an adjustable drawing-head with rules attached to a protractor scale so that the angle of the rules may be adjusted.

A drafting machine allows easy drawing of parallel lines over the paper. The adjustable angle between the rulers allows the lines to be drawn in varying accurate angles. Rulers may also be used as a support for separate special rulers and letter templates. The rules are replaceable and they can be for example scale-rules.

Drawing apparatus has evolved from a drawing board mounted parallel ruler and a pantograph, which is a device used for copying objects in an adjustable ratio of sizes.

• Rulers

Rulers used in technical drawing are usually made of polystyrene. Rulers come in two types according to the design of their edge. Straight edge can be used with lead and felt pens, whereas when technical pen is used the edge must be grooved to prevent the spread of the ink.

Architect's scale is a scaled, three-edged ruler which has six different scales marked to its sides. A typical combination for buildings details is 1:20, 1:50, 1:100, 1:25, 1:75 and 1:125. There are their own rulers for zoning work as well as for inch units. Today scale rulers are made of plastic, formerly of hardwood. A pocket-sized version is also available, with scales printed on flexible plastic stripes

Sectional Views

INTRODUCTION

In engineering drawing, various objects have invisible or hidden interior features, which are represented by dotted lines in their projection views. But, when the features, are too many, the orthographic projections obtained get complicated and difficult to understand. In order to understand the interior view details, the object is cut an imaginary cutting plane called Sectional Plane. The part of the object between the cutting plane and the observer is assumed to be removed and view is then shown in section. The view thus obtained is called Sectional View.

Sectional View

The view obtained by cutting an object with an imaginary cutting plane is called Sectional View.

The surface produced by cutting the object by the section plane is called Section. It is indicated by thin section lines uniformly spaced, generally at an angle of 45'. As already imagined, a sectional view is a view seen when a portion of the object nearest to the observer is imagined to be removed by means of a cutting plane or planes, thus revealing the interior construction.  The other views are not affected in any way always represent the entire object.

Types Of  Sectional Views

The sectional views are of mainly two types. These are dependent upon the number of cutting planes cutting the object.

1. Full Sectional View.
2. Half Sectional View.

Full Sectional View

The view obtained after removing the front half portion of an object is called a Full Sectional Views or Front Sectional Views or Simply Sectional Elevation.

When the cutting plane cuts the object lengthwise, full sectional front view is obtained. It is also called longitudinal section. It may be noted that the top view or the slide remain unaffected, that means top view is drawn full not half.

The Cutting Plane 

• The cutting plane is shown in a view adjacent to the sectional view.
• In the section view, the areas that would have been in actual contact with the cutting plane are show with section lining.

Lines Behind the Cutting Plane

• The visible edges of the object behind the cutting plane are generally shown because they are now visible but they are not cross-hatched.

The Cutting Plane

Placement of Section Views

• Section views can replace the normal top, front, side, or other standard orthographic view.

Placement of Section Views

Labeling Cutting Planes

• When more than one cutting plane is used, it is especially important to label them for clarity.

Line Precedence

• When a cutting plane coincides with a center line, the cutting plane line takes precedence.
• When a cutting plane line would obscure important details, just the ends of the line outside the view and the arrows can be shown.

Rules for Lines

• Show edges and contours which are now visible behind the cutting plane.
• Omit hidden lines in section views.
• A section-lined area is always completely bounded by a visible outline.
• The section lines in all hatched areas for that object must be parallel.
• Visible lines never cross section lined areas.

Section Line Mistakes

Cutting Plane Line Style

• Cutting lines are thick lines (0.7 mm).
• The preferred cutting plane line style is made up of equal dashes ending in arrowheads.

Section Line Technique

• Uniformly spaced by an interval of about .10”
• Uniformly thin, not varying thickness
• Do not run beyond outer edges of the visible lines
• Usually at 45˚ angle

Section Line Mistakes

Section Line Technique

Section Lining Symbols

Half Sections

The view obtained after removing the front quarter i.e. one  fourth portion of an object by means of two cutting planes at right angle to each other is called Half Sectional View or Half Sectional Elevation.

It may be observed that the plane or top view also remain unaffected i.e. full side view is drawn.