Extend Surface only sees partial edge on simple surface

I have a simple arc sweep 1 rail 9mm then 11mm then 14mm rad arcs.

One simple surface !

ExtendSurface refuses to see the entire edge to extend this onwards as if I had 17mm or whatever arc.

Why ?

Simple things that refuse to work…grrrr !

Is there by the way a sweep I can do that will not stop at the 14mm rad curve but continue deveoping the increasing radius arc ?

I would like the extendSrf apart from actually recognising the surface edge, also to give me a drag to extend option rather than just ask for an extension factor.
I can see where I want to extend it to, not fully along the rail but near the end, and would like to drag extend, like one can create a solid and see it move up and down.

I havent a clue what extension factor my distance is, its a visual thing is 3D and I extend and snap to a location, extension factors dont get used much with me !
ExtendSurface.3dm (43.8 KB)
Do others agree with this lack of option ?


Hi Steve- the sweep is a two surface polysurface. You’ll have to explode and extend each, though I think another section curve for Sweep might be a better bet. ( I see that your arcs are all 90 degrees but they are structured differently- I am not sure why that is, but that is why it is making a polysurface. I’ll see if we can force simplifying 90 degree arcs to the simplest structure)

The extension factor is problematic- except in simple cases, the actual amount extended is not constant across the entire edge. Also extension is calculated in the surface parameter space and not 3d space, so that is another complication.
I would over-build this and cut it back to where you like it. I agree it would be nice to be able to extend with more precision on freeform surfaces.


Hi Pascal.
To make the arcs I simple drew circles in ortho view, then cut them to quarters there, I dont understand why they differ, same circle tool, just different rads. Then each one was 3d rotated in perspective view and taken out from the centre line and met up with the rail.
So to see this become two surfaces from that simple act of trimmed circles swept to 1 rail is odd. very odd.

Do others get such strange things happen or is it just me ?

Doesnt half ruin ones evening, had hope to finish and have meal hours ago.

you lost me there a bit.

The circle diameter and progression didnt seem easily estimated for the next one, they dont all lie on a straight line at their lower edges else I could have added another arc. They were from a plan and they didnt indicate the last radius !


Hi Steve - how did you cut them into quarters? I ask because cutting a circle into 90 degree arcs should result in 3 point arcs even of splits are not on the spans of the circle. You ended up with one 3 point arc and two that are 5 point- I’d like to reproduce that- it seems wrong to me.