Identifying/Avoiding Topological Naming Problems

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
Workshop_Notes
Posts: 591
Joined: Wed Sep 29, 2021 8:35 am

Re: Identifying/Avoiding Topological Naming Problems

Post by Workshop_Notes »

teletypeguy wrote: Fri Jun 02, 2023 9:13 pm ...how I could identify them from the dependency graph...
It may or may not help but there is a woodworking workbench, (https://github.com/dprojects/Woodworking). Maybe you could make the same thing as you have made using that and compare dependency graphs.
chrisb
Veteran
Posts: 53945
Joined: Tue Mar 17, 2015 9:14 am

Re: Identifying/Avoiding Topological Naming Problems

Post by chrisb »

teletypeguy wrote: Fri Jun 02, 2023 10:51 pm It does not really need a datum plane to offset then, does it? A datum plane can be generated on the base plane, then offset and sketch on it, but I now find that I can just sketch on the base plane and then offset the sketch. Seems like same result, so is the datum plane unnecessary in this offset case?
Exactly! You don't need the DatumPlane here, and it would not change the topological naming issues if you used one. I almost always use Sketches without DatumPlanes.
To avoid issues and yet ease the placement of sketches, you should have a look at the Basic Attachment Tutorial.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
drmacro
Veteran
Posts: 8872
Joined: Sun Mar 02, 2014 4:35 pm

Re: Identifying/Avoiding Topological Naming Problems

Post by drmacro »

teletypeguy wrote: Fri Jun 02, 2023 10:51 pm
drmacro wrote: Fri Jun 02, 2023 10:04 pm The best is to create a sketch attached to a base plane and use the Attachment>Position property to adjust the location of the sketch. Many times this is done with an expression referencing Pad.Length for example.
I see. That is easy enough to do when starting a new project so I will try to get in the habit of offsetting. It does not really need a datum plane to offset then, does it? A datum plane can be generated on the base plane, then offset and sketch on it, but I now find that I can just sketch on the base plane and then offset the sketch. Seems like same result, so is the datum plane unnecessary in this offset case?
thx
There are very few instances the require a Datum plane. The are handy for use as arbitrary mirror planes, if you need to place a sketch at a specific angled offset from the origin, or if you are going to have multiple sketches that need the same arbitrary offset. In other cases the Datum is redundant/superfluous.
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
User avatar
Shalmeneser
Veteran
Posts: 9475
Joined: Wed Dec 23, 2020 12:04 am
Location: Fr

Re: Identifying/Avoiding Topological Naming Problems

Post by Shalmeneser »

drmacro wrote: Sat Jun 03, 2023 9:38 am There are very few instances the require a Datum plane. The are handy for use as arbitrary mirror planes, if you need to place a sketch at a specific angled offset from the origin, or if you are going to have multiple sketches that need the same arbitrary offset. In other cases the Datum is redundant/superfluous.
Should we add this text to the wiki (PartDesign_Plane) ?

With the caveat about TNP :
DatumPlanes or sketches attached to a face are prone to TNP.
drmacro
Veteran
Posts: 8872
Joined: Sun Mar 02, 2014 4:35 pm

Re: Identifying/Avoiding Topological Naming Problems

Post by drmacro »

Shalmeneser wrote: Sat Jun 03, 2023 2:53 pm
drmacro wrote: Sat Jun 03, 2023 9:38 am There are very few instances the require a Datum plane. The are handy for use as arbitrary mirror planes, if you need to place a sketch at a specific angled offset from the origin, or if you are going to have multiple sketches that need the same arbitrary offset. In other cases the Datum is redundant/superfluous.
Should we add this text to the wiki (PartDesign_Plane) ?

With the caveat about TNP :
DatumPlanes or sketches attached to a face are prone to TNP.
Only if my typos are corrected :oops: :
"There are very few instances the require a Datum plane. They are handy for use as arbitrary mirror planes, if you need to place a sketch at a specific angled offset from the origin, or if you are going to have multiple sketches that need the same arbitrary offset. In other cases the Datum is redundant/superfluous.
"
And the TNP caveat:

"DatumPlanes or sketches attached to any generated geometry (edge/face) are prone to TNP."
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
User avatar
teletypeguy
Posts: 96
Joined: Thu Jun 01, 2023 8:41 pm

Re: Identifying/Avoiding Topological Naming Problems

Post by teletypeguy »

Datum planes for mirroring, angling wrt base planes, and more than one sketch on the plane -- got it. And create the datum on a base plane and move it from there. Never create datum plane from a face. I will try to only use them when needed.

I spent a little time leaning on solidworks when a buddy was teaching me the basics of solid modeling. I got used to using sw "reference planes" and found them handy. I made a little enclosure for a pcb and added a ref plane for top of pcb so I could use that when cutting connector openings and so on. I am unclear whether the sw ref plane was a global thing or attached to the body. Doesn't matter as I am going to use FC now, so I just need to learn the "best practices" as they say, to try and not get into trouble.
User avatar
teletypeguy
Posts: 96
Joined: Thu Jun 01, 2023 8:41 pm

Re: Identifying/Avoiding Topological Naming Problems

Post by teletypeguy »

Workshop_Notes wrote: Sat Jun 03, 2023 9:06 am ...there is a woodworking workbench, (https://github.com/dprojects/Woodworking). Maybe you could make the same thing as you have made using that and compare dependency graphs.
That looks interesting. It says it is only tested on linux freecad, so I will try it on my pop-os (ubuntu-based) install of freecad. But heading off on a trip so will be a few weeks until I get a chance to try it. thx.
Post Reply