how original parts or models of machinery is made.

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How are machines parts made so exactly. I assume there is a master model that all lives are made from but how are those master models created so precisely and how are they measured.

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There’s a variety of manufacturing methods used to create machine parts.

The “simplest” is to create the parts from stock material in a workshop, piece by piece, using lathes, mills, etc to precisely machine down each piece to the required specifications.

When designing a machine, the entire thing will be modelled in CAD, with each part being inspected for conflicts with other parts.
From this CAD model, parts will be assigned tolerances, which will determine the minimum and maximum size each part can be and still work.

As for measurement, measuring tools are calibrated against known standards, so that each tool agrees with each other. There is some tolerance in this process, which needs to be understood.

This is a very simplistic look at design and manufacture.

1) A lot of design work is done on computers using CAD. These are electronic design files that allow the designer to check their work and ensure they get the parts modelled correctly before fabrication

2) Complex equipment are typically broken down into major sections. Each section is designed to fit into the whole machine. Different people will be in charge of designing their own sections. This reduces the design time. Some sections, motors etc, might be purchased – a designer can select these components from a standard catalog.

3) Standardization. Many parts are standardized like screws, nuts, bolts and electronic components. Rather than designing things from scratch, the CAD tools already “recognize” these standard parts and sizes. So the designer just has to place a predesigned part into their model.

Any complex equipment will have many prototypes. Some prototypes are for fit – ie the parts might not work but are there just to ensure that they fit together. Others are functional prototypes – they are designed to mimic the function but not necessarily the appearance. Some are appearance models – for example car manufacturers might build a full scale model out of clay just to have a sense. Some are test models – to test reliability and functionality.

Designing large equipment is a complex task usually requiring the collaboration of many people, each with some particular expertise mechanical, electrical, thermal, noise etc.

Comes in two parts, engineering and manufacturing. Engineers create the design, these days in computer models, but historically sketched on paper. Output of their work is manufacturing documentation. That includes drawings, circuit diagrams, 3D model files for CNC, bills of materials etc, it’s the complete specification needed to build the machine. For manufacturing it’s a matter of dividing up the labor, lots of parts are off the shelf and you have to buy them, a lot of metal work you can outsource or make in your own machine shop. Once you have all you need, then it’s assembly, putting it together according to drawings. Oh, and software, better not forget about that or your machine is a gigantic paperweight.

Of course, no real machine build is this straight forward. Engineers make mistakes, fail to foresee problems, manufacturing parts doesn’t always turn out right, mistakes happen and sometimes you only find out when putting the thing together or trying to get it working. Assembly mistakes also happen, it’s easy to connect something wrong and have it go up in smoke. Software of course is an endless source or difficulties on anything but the simplest machines. It’s a constant back and forth between all parties involved to sort out problems and get the machine up and running.

Lots of detailed answers here. I just want to add that when it comes to measurement, you could use something called a gage block set. It is basically a set of blocks that have been precision made to be exactly a certain length (1mm, 2mm, etc). You use these blocks to calibrate your machine so when your machine says 1mm you can be sure that it’s actually 1mm, not 1.5mm or 0.99mm. These blocks are made in such a way that they have very low tolerances, depending on their grade, with tolerances around 0.0003mm on a 1mm block for an example.

Of course this isn’t the only way to calibrate machineries. You could use high precision sensors too for things like semiconductor production. But it’s the simplest one to do. There’s an entire field just based around how we measure stuff it’s fascinating.