TNP problem understanding how to get around it

[drmacro]

Hows is hiding the pad going to help?

The datum plane is not necessary with this example I know I could detach the sketch and accomplish the same thing but the datum plane is an easy way to get a sketch (or multiple) in the correct orientation.

But this doesn't solve my underlying problem. How do I create a sketch while using the external geometry tool but not have it dependent on the external geometry ?

Is there now way around the TNP?

External geometry referenced to sketch geometry is less prone to TNP, but not immune.

External geometry attached to generated geometry is very prone to TNP. So hiding generated geometry and selecting sketch geometry is better.

Using expressions avoids TNP, when expressions can be used. For example, using a expression for the Attachment offset Z that references Pad.Length moves the sketch to the top of the Pad (assuming it is padded in the Z direction). And there is no TNP, since no geometry (edge, face, vertex) names are used.

The possibility of TNP can be reduced by good modelling techniques, but, it is a side effect in all parametric modellers.

[jmanatee]

Starting to understand... I tried it referencing the pads sketch and that worked,

I am understand using the expression to get the placement,

Still curious why in that video his version of freecad the external geometry tool didn't create the External Geometry parameter.

[drmacro]

...
Still curious why in that video his version of freecad the external geometry tool didn't create the External Geometry parameter.

He is working in 0.18. Things are somewhat different in later versions.

[jmanatee]

It would be nice to have a tool similar to the external geometry tool but just created construction geometry

Or to be able to convert the external geometry to construction geometry

Thanks for everyone's help

[chrisb]

It would be nice to have a tool similar to the external geometry tool but just created construction geometry

Or to be able to convert the external geometry to construction geometry

Why would you do that? External geometry i as good as - immutable - construction geometry.

[jmanatee]

It would be nice to have a tool similar to the external geometry tool but just created construction geometry

Or to be able to convert the external geometry to construction geometry

Why would you do that? External geometry i as good as - immutable - construction geometry.

External geometry is only immutable if the base object isn't changed. So using the external geometry tool can cause the TNP.

My goal is to be able to grab the edge of the base object to be able to set position of items in the current sketch and not have the TNP occur if the base sketch changes.

Not sure this actually matters in real life use of freecad. But as I am learning I came across several articles and videos discussing the TNP and ways to avoid it. So I went down a rabbit hole trying to figure this out. Basically as I better understand what causes the TNP, I will know how to avoid creating it.