MYP Design Exploded and Assembly Drawings Notes

One Drawing Replaces a Paragraph of Instructions

1. An exploded view pulls every part of a product apart and floats it just clear of where it belongs.
2. Written out, one joint might read "pass the M4 bolt through the bracket, add the washer, then the spacer, then tighten the nut".
3. Drawn exploded, that same joint is understood in about two seconds and in any language.
4. It answers three questions at once: what parts exist, what order they go in, and which way round each one faces.
5. Most exploded views are drawn on isometric axes, because parted lines stay parallel and the eye can follow them.

Centre Lines of Assembly Hold Everything in Order

1. A centre line of assembly is a long dash short dash chain line running through every part that shares one axis.
2. Each part is slid along that line away from its neighbour, never sideways, so the reader can see it drop straight back into place.
3. The bolt, washer, bracket and nut of one joint all sit on a single centre line, which is what makes the order obvious.
4. A product with three different joints gets three centre lines, one for each group of parts.
5. If a part has to move along two different directions to come out, explode it along the one it is fitted on and say the rest in a note.
6. Draw the centre lines faint and thin, because they are guides and the parts are the subject.

Spacing Tells the Story of the Build

1. Leave a clear gap between parts so that no two outlines touch or overlap anywhere on the drawing.
2. Keep the gaps roughly even, since a huge gap suggests a part comes from somewhere else entirely.
3. Arrange parts in the order they are fitted, reading left to right or bottom to top, so the drawing doubles as a build sequence.
4. Keep the largest part, usually the base or the main body, in place and explode the smaller parts away from it.
5. Draw every part at the same scale, so a 6 mm washer stays six times smaller than a 36 mm disc.

Part Numbers and a Parts List Do the Naming

1. Each part gets a number in a small circle, called a balloon, joined to the part by a thin leader line.
2. Number in assembly order, or work steadily round the drawing, so the numbers never jump about the page.
3. The parts list then explains each number once, which keeps the drawing itself clean of text.
4. Give it columns for item number, part name, quantity, material and size, and put it just above the title block.
5. Bought in parts are described by their standard name, so "M4 x 25 hex bolt" is enough for anyone to order the right thing.
6. The quantity column doubles as your shopping list when you cost the project.

A parts list for a simple desk lamp base

An Assembly Drawing Shows the Finished Thing

1. An assembly drawing shows all the parts in their final positions, fitted together as the product will be used.
2. It demonstrates that the parts go together, since a joint that works in your head sometimes collides once everything is drawn in place.
3. A sectional view, drawn as though the product were sliced through, shows what is happening inside a housing that is otherwise sealed.
4. Cut surfaces in a section are filled with even diagonal hatching at 45 degrees, and touching parts are hatched in opposite directions.
5. Assembly drawings carry only the sizes that matter when parts meet, such as the overall height, not every dimension of every part.

Drawing One Without Making a Mess

1. Count your parts first and pick a sheet size that gives each of them room, because a cramped exploded view is unreadable.
2. Group a screwed together sub unit as a sub assembly and explode it on its own drawing, rather than showing forty parts at once.
3. Keep line weight consistent: thick outlines for the parts, thin lines for centre lines, leaders and balloons.
4. CAD software will generate an exploded view from a model, but you still choose the direction, the spacing and the numbering.
5. Test the drawing by handing it to someone who has never seen your product and asking them to describe the build order.

Choosing Between Exploded, Assembled and Flat Views

1. Use an exploded view whenever somebody has to put the product together, take it apart or replace a worn part.
2. Use an assembly drawing when the question is what the finished product looks like and how tall it ends up.
3. Use a dimensioned flat view for each individual part, since neither of the other two carries enough sizes to make anything from.
4. In a design folder the exploded view usually earns its place on the manufacturing plan page, next to the parts list and the sequence of operations.