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You have a design problem statement, which gives you numerical specifications for performance, spatial constraints etc, and you have finally come up with some mechanism ideas you synthesised into a machine concept.

You’ve sketched your design’s parts and the final assembly.

So: How do you now go about calculating the dimensions of your undimensioned design?

tripleee
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Hisham
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    I don't see how you can sketch something and have no idea about what particular dimensions they should be. You might not know the *exact* dimensions but surely you have some idea. – DKNguyen Sep 27 '22 at 04:49
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    The way an engineer works is different based on many outside parameters (experience, problem, training etc). There is no gold standard or universally accepted way, so this is very much opinion based. So in my opinion you'd a rough sketch of ideas and try to identify the key elements in the design, and try to size them by rough calculations (ignoring computationally intensive calcs as much as possible). IF there is any previous experience you can build on that (e.g if you are asked to size the ducts in an AC system in a building and you've already done a similar building) – NMech Sep 27 '22 at 05:51
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    A part of engineering is to quantify the unquantifiable. Calculus, numerical analysis, measurements, guesstimation, models, simulations, whatever gets the job done. – StainlessSteelRat Sep 28 '22 at 02:42
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    If the design is going to interact with the real world in some way, that will determine the scale. – Drew Sep 29 '22 at 05:19

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If you use parts, such as gears, screws, pulleys, etc., they are available in different sizes; it's less expensive to purchase an existing size part, as opposed to custom manufacturing something, but sometimes it's necessary to use a minimum number of customized parts to consolidate a portion of the mechanism.

The material you use to manufacture your device has various qualities such as melting point, elongation or bendability, and strength; these qualities must be sufficient to ensure the life of the device.

Your device may require certain properties such as salt resistance, polishability, recyclability, etc.

All those factors and more go into the design, that also must be balanced with cost and availability. This doesn't have a short simple answer, and the answer varies for each device and its application, etc.

Rob
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