General > General Technical Chat

Do tables of XY coordinates tarnish the souls of engineers?

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filssavi:
I think it’s more lazyness and tradition than anything else

The MCAD workflows are designed to automate a certain typical style of diagram, which is the traditional one, for anything else you probably would have to fight with the tool, or at least take three times as much as you would do normally. This would be worthwhile if the creators of said diagrams were also the users, however I am willing to bet  in a vast majority of cases the mech engineers never even spoke with a PCB designer, let alone tried himself.

And for the silicon vendors, there is absolutely no economic incentive to change things

Rerouter:
I think its more a case of its one of the last steps, so slap down enough measurements to make it reproducable, but no real thought as to making it easy to model,

Atleast on the up side, more manufacturers are starting to produce footprints for various CAD packages. even if you still have to verify them,

It seems USB connectors / SD card connecors / Sim card connectors are some of the worst offenders as they have different offsets as that keeps all the pins the same shape in manufacturing.

Kicad hs some plugins that let you quickly rebuild it doing the intermediate steps for you, but I haven't used them myself.

penfold:
When you are verifying the footprint, it is much easier to measure horizontal and vertical distances to the edge of a pad or feature than it is to guess an arbitrary centre or make two measurements to average (maybe your cad program has the option to place the pad origin away from its measured centre or perhaps one might be doing this in Gerber format... the component manufacturer doesn't know).
There may even be some valid engineering reasons to offset a pad or alter its dimensions slightly in which case you are perhaps more interested in verifying that you haven't ridiculously exceeded the recommendations of the edges of the pad w.r.t an origin that's easy to measure to or even a creepage/clearance constraint, again which need to be measured to an edge.

Circles and holes are also a special case for so many reasons, but I believe they're a Gerber primitive or most Gerber viewers can pick up the drill file to place centre markers.

I would imagine the reason they have been presented for so long in such a manner is that manufacturers have never been able to find a compromise between the "information you need to build the footprint" and "information that's more helpful when measuring" so they simply give you the information that they would use to verify your footprint should you complain to them.. and leave it at that to avoid confusion.

Berni:
Yeah i absolutely hate these kind of drawings too.

Id say its just laziness. The thing likely exists as a drawing in a 3D mechanical CAD. When turning it into a drawing the designer can easily click edges and plonk down dimensions. So he just clicks enough edges to make it unambiguous. Drawing centers would require extra work to do.

But yeah some of it is probably that mechanical engineers find this form of measurements makes "more sense" because its how its usually done, and that way tends to work better for simpler drawings of most mechanical parts.

Brumby:
The documentation stage in any IT project has to be one of THE least tasks to be given appropriate time allocation - especially if the project has made it to implementation.  A management decision.

I can see the same "logic" occurring in other disciplines.

I'd bet there are many engineers just grimacing at the drawings they've been forced to leave because they're "good enough".

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