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Off Topic Hobbies => Mechanical Engineering => Topic started by: gnuarm on February 07, 2021, 06:53:55 pm

Title: Origin and Axes in CAD
Post by: gnuarm on February 07, 2021, 06:53:55 pm
I recently found out that KiCAD defaults to to the origin being in the upper left corner of the drawing and positive being down.  I'm told that in mechanical design the origin is typically in the lower left corner and positive is up.  Is that true?  If working on the mechanical aspects of a design how much does it matter that information on the PCB is oriented differently. 

Has anyone had a problem communicating information between EDA tools and CAD tools because of this?
Title: Re: Origin and Axes in CAD
Post by: fourfathom on February 07, 2021, 06:57:56 pm
I've been able to work around the KiCad origin issue with little or no problem, but it is a detail that can be annoying.

But the new KiCad v6 release will apparently fix this, putting the origin at bottom-left, and the + directions up and to the right.  Here's a thread on v6: https://www.eevblog.com/forum/kicad/kicad-6-is-coming!/ (https://www.eevblog.com/forum/kicad/kicad-6-is-coming!/)
Title: Re: Origin and Axes in CAD
Post by: gnuarm on February 07, 2021, 07:06:07 pm
Yes, thanks.  I am aware that the problem has been resolved in KiCAD and now you only need to change from the default.  i was just wondering how much of an issue it was in the first place. 

For me it would involve remapping everything when working with the software since the mechanical guy would be working in one orientation and my layout software would be working in another.  I don't know what issues might result when using CAD generated data.  The project I am currently on uses KiCAD (not the new release with the axis fix) and the mechanical design exchanges 3D data with KiCAD.  I suppose that is via a standard and automatically converts the axes. 
Title: Re: Origin and Axes in CAD
Post by: JohnnyMalaria on February 07, 2021, 08:27:54 pm
Presumably, it creates the Gerber files with the standard axis orientation otherwise PCBs would come back mirrored. It doesn't seem to be an real issue. FWIW, Windows GDI has the origin at top-left which maybe is why KiCAD evolved that way.
Title: Re: Origin and Axes in CAD
Post by: gnuarm on February 07, 2021, 11:04:20 pm
Not really talking about the Gerber files.  Every board needs to be mounted and often they have connectors which have to line up with the openings in cases.  I've even seen connectors that are fastened to the case as well as the PCB.  In those cases there has to be a common framework for communications. 

That's what I'm asking about.  Do people have problems when the PCB layout tool uses a different frame of reference, or is that already worked out? 
Title: Re: Origin and Axes in CAD
Post by: Bassman59 on February 09, 2021, 07:31:05 pm
Not really talking about the Gerber files.  Every board needs to be mounted and often they have connectors which have to line up with the openings in cases.  I've even seen connectors that are fastened to the case as well as the PCB.  In those cases there has to be a common framework for communications. 

That's what I'm asking about.  Do people have problems when the PCB layout tool uses a different frame of reference, or is that already worked out?

I regularly import the STEP files of board assemblies generated by Kicad into Fusion360. I'm still on 5.1.9 which uses the "Y increasing as it goes down" TV raster format.

There's always some fussing with orientation. F360 has the "top" of an assembly parallel to the X-Z plane, with Y increasing up. See the picture. The imported STEP files seem to have the positive Z axis going up, with the plane of your table (say) as X-Y.

Of course the PCB assembly is "correct" and not mirror image or inverted somehow. It just has to be oriented as you need. So it's always fun to import, say, a STEP model of a Hammond extruded enclosure, and then import the PCBA model, and flip and rotate one with respect to the other to get them lined up.

Now further on this, I have a 3D printer, which is handy for making enclosures. The printer considers the plate to be the X-Y axis, with the origin to be (as you face the printer) the left front of the plate. The Z axis is up. And every time I bring an STL from F360 into Cura for slicing, it has to be flipped/rotated and aligned on the plate. [attach=1] What Fusion considers the "top" and how Cura views the print surface are different.

So all of this is to say that origin and direction just seem to work themselves out.
Title: Re: Origin and Axes in CAD
Post by: beanflying on February 14, 2021, 04:49:29 am
With Fusion there is under preferences the ability to switch the axis around. Generally I don't fuss to much as flipping models to print or Laser cut is still fairly simple post Fusion.
Title: Re: Origin and Axes in CAD
Post by: jmelson on February 19, 2021, 05:03:16 pm
I recently found out that KiCAD defaults to to the origin being in the upper left corner of the drawing and positive being down.  I'm told that in mechanical design the origin is typically in the lower left corner and positive is up.  Is that true?  If working on the mechanical aspects of a design how much does it matter that information on the PCB is oriented differently. 

Has anyone had a problem communicating information between EDA tools and CAD tools because of this?
Hmm, a bit odd.  But, I'm pretty sure you can move the origin to anywhere you want it to be.  I think if Y+ was down I would have noticed that when making Gerbers or pick and place files.  It may well be a configuration parameter hidden in a menu somewhere.

Jon