NOTES TECHNICAL DRAWING Technical drawing is all about clear, thorough and precise communication of the Subject. A good set of technical drawings will clearly communicate all aspects of a product – size, detail, assembly, materials, parts etc. and allow someone to build the product without any further information. Here are some things to remember:

Fig. 1. Pawson, Sandy (2005). Black Diamond Headlamp Orthographic Drawing. Sandy Pawson 2008

NOTES TECHNICAL DRAWING GENERAL

• If you are using a computer to generate your technical drawings take

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the time to set up settings/ preferences before you start drawing as this means they will be the same across all your drawings. Particularly things like dimension, tolerance and text presets. There are some example boards of 1st and 3rd angle projection in the workshop on the north wall by the roller door and clearly explain how to layout your orthographic drawings. Always get someone to check your drawings over and take some time doing so – preferably someone who is familiar with technical drawing. It is useful to boost the line weight of the outline of your object to clearly define the edges. Hand drawn technical drawings are just as usable as computergenerated drawings (and in some cases easier to create). However, hand drawn drawings still need to be precise, so if you choose to do them by hand take time over them, use draughting film (you can trace over underlaid drawings and scratch off unwanted ink lines).

Fig 2. 1 st (ON LEFT) & 3rd (ON RIGHT) angle projection symbols. http://en.wikipedia.org/wiki/Engineering_drawing. Retrieved 27/08/08

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LAYOUT The layout of your drawings should provide absolute clarity and allow the reader to easily understand your product. Here are some tips for layout. Consistently use the same title block, font, border etc. across your drawings. This gives your drawings uniformity and ties your drawings together as one set (see Fig 1.). Ensure all orthographic views are laid out according to the projection style stated (see Fig 2.). Clearly label your views – in the title blocks (as the drawing title) and in the drawing if multiple views are on one page (Plan, front elevation etc). Use an appropriate drawing scale (usually 1:1, 1:2, 1:5, 1:10, 1:25 etc. not 1:1.33). General assembly drawings need to be a consistent scale (if on one sheet or many) but parts, auxiliary or section views should be drawn to a scale that fits the page. Any sizeable blocks of text (notes, parts lists etc.) should be located in the title block. Small isolated notes can be on the drawing (preferably in grey) if they do not clutter the page. Use centre lines to indicate a symmetrical view, circle centres, radius centres or pivot points (see Fig 3.).

Sandy Pawson 2008

NOTES TECHNICAL DRAWING • Always show where a section view is cut with a labelled cutting line and indicate which way the view is orientated (see Fig 4.). If the section view is on a supplementary drawing make a note of the drawing number where it can be found.

Fig. 3 Technical Drawing Line Types & weights. http://en.wikipedia.org/wiki/Engineering_drawing. Retrieved 27/08/08

Fig. 4. Pawson, Sandy (2005). Black Diamond Headlamp: Section Drawing.

Sandy Pawson 2008

NOTES TECHNICAL DRAWING

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TEXT All Text on your Drawings should be clear and easy to read. Ensure all text is: Of an appropriate size – Avoid smaller than 10pt if possible. In a clear font – Avoid decorative or elaborate fonts. Spelt correctly – enough said. Concise – All text should be straight to the point. If you are handwriting text use guides to ensure it is straight, use a pen or sharp dark pencil and really consider your handwriting – scrawled, sketchy or overwritten notes look untidy! Text used for dimensions, numbering, notes etc. can be in 50% grey to aid clarity, Drawing names (plan, section AA) should be in black. THE TITLE BLOCK The Title Block should be clear concise and easy to read. It is traditionally positioned along the bottom of the page in a separate ruled partition. Every Title Block should contain: Title – name of the product. Drawing Title – general assembly, exploded view, section AA etc. Drawing Number – 01 of 08. Date Drawn – 08/08/08 Drawn By – (your name) Checked By – name of person who checked them. Scale of Drawing – 1:1 (full size) 5:1 (5 times larger than product). Units – dimensions in mm, meters, inches, etc. Tolerances - all measurements ±0.5mm, all angles ±0.5°. A space for Notes. A space for Revisions. Orthographic Title Blocks should contain: The type of projection used and the appropriate symbol – third angle projection. Exploded / Assembly Drawing Title Blocks should contain: Parts List – Numbered, inclusive list of all product parts correlating to the numbered parts in the drawing (include things like screws eg 2 x M6 by 8mm Screws, cheese head, square drive, zinc coated) Part Drawing Title Blocks should contain the following information: Part Number – as indicated on an exploded view or assembly drawing. Number Required – for the product. Material – of the part & Process of forming (injection moulded LDPE) Finish – of the part (spark eroded) Colour – of the part (if varied or unknown indicate this) If you are not doing parts drawings the material, finish, number required and colour information should be included elsewhere in your drawings (normally on an exploded or assembly drawing).

Sandy Pawson 2008

NOTES TECHNICAL DRAWING

Fig 5. Datum Dimensioning – From a line left) and a centre (right). http://www.engin.brown.edu/courses/En174/Dimensioning.htm. Retrieved 27/08/08

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DIMENSIONING Dimensioning is a key aspect of all technical drawing. The aim of dimensioning is to convey all required accurate (to your tolerances), clear dimensions as clearly as possible. Ensure all Dimensions are: Of an appropriate text size – Avoid smaller than 10pt if possible. Grey in colour – Around 50% minimises drawing clutter. Within your tolerances – Don’t show dimensions to three decimal places if your tolerances are one decimal place. Have leader lines that extend to roughly 2mm from the points you are dimensioning to. Avoid overlapping leader lines. Referenced from a datum – measure all dimensions from a common edge, point or centre line to avoid progressive error (see Fig 5.). Written horizontal or vertical so they are readable from the bottom or right edge of the page. Diameter dimensions are indicated correctly – ∅ 25mm Radii dimensions are indicated correctly – R 10mm Angle Dimensions are indicated correctly – 30° Avoid placing dimensions inside a drawing – place them along side the views extending leader lines if necessary. Avoid using horizontal or vertical leader lines when indicating internal dimensions (see Fig 6.).

Sandy Pawson 2008

NOTES TECHNICAL DRAWING

Fig 6. Pawson, Sandy (2005). Black Diamond Headlamp: Dimensioning correction

ORTHOGRAPHIC DRAWING An orthographic drawing (sometimes called a general assembly drawing) is a layout of plan and elevation views of a product according to standard conventions. Orthographic views are laid out in either 1st angle projection or 3rd angle projection and are essentially a set of scaled, associated views suitable for dimensioning to define a product or part. Orthographic views should: • Arrange views according to your chosen projection method, with each view equally spaced and aligned (see Fig 1.). • Include your chosen projection method in your title block (see Fig 2.). • It can help to include a labelled pictorial (generally isometric) view along side your orthographic views to aid in the interpretation of your drawing (particularly when people unfamiliar with orthographic are using the drawings).

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SECTION VIEWS A Section or Cut-Away view shows the internal workings of a product cut through a labelled plane. This allows us to show assembled parts and hidden detail invisible from the outside. Ensure all section drawings: Are labelled according to the cutting plane – Section AA (see Fig 4.). Have the cutting plane shown on a related drawing including the side from which it is viewed. If this is on a separate page note the drawing number where it can be found. If you are showing a section view on an orthographic drawing ensure it is orientated according to your projection method – a section view viewed from the left will appear on the left in third angle projection, and on the right in first angle projection. Are hatched appropriately – each separate part hatched in a different direction (never hatch vertical or horizontal). Rods & Screws are not hatched (see Fig 4.).

Sandy Pawson 2008

NOTES TECHNICAL DRAWING

Fig. 7. Raleigh Gran Sport DL160 Exploded Drawing. http://www.sheldonbrown.com/retroraleighs/catalogs/1977-drawings/pages/12-gransport.html. Retrieved 27/08/08

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EXPLODED VIEWS An exploded view shows all the parts of a product and how they fit together. These drawings are usually in a pictorial view (isometric, perspective etc.) and have less stringent conventions, however it is good to remember the following: Explode the components a constant distance (eg 20mm between each part) to keep a uniform look. Exploded views generally are not dimensioned. Show where components line up (screw points etc.) with dotted lines. If you are using perspective as the basis of the exploded make sure it is appropriate to your product scale. If you are rendering the exploded view it can help to turn shadows off as they sometimes complicate the drawing (especially when cast onto a ‘floor’ plane). If you are using the exploded drawing to number parts (for a parts list) make sure these numbers (or letters) and arrows are in 50% grey and are numerical down the page (1, 2, 3… not 5, 2, 12… see Fig 7).

Sandy Pawson 2008