Create curve arc three

Coreform Cubit
#1

version 2020.2
windows 64

I am having what seems to be a tolerance issue with “create curve arc three”. all three curves are coplanar, but I get an ACIS error when I enter

create curve arc three curve 1 2 3 full

Is there a tolerance setting that lets this command work?

image
image796×414 2.05 KB
cubit02.cub (12.0 KB)

#2

What are you expecting for a result?
The documentation for this command states:

6 . Arc Three: The following command creates an arc either through 3 vertices or tangent to 3 curves. The Full qualifier will cause a complete circle to be created.

The ACIS geometry engine cannot find the arc tangent point on the circles so it fails.

This is a more common use case.

image

#3

It should (and sometimes does) give this result

ideal
ideal620×647 31.2 KB

If it fails, I discovered a workaround. By extending the line, Cubit draws the circle on the other side:
workaround
workaround620×647 31.9 KB

Then I have to make a series of geometric transformations to mirror the circle to the correct position.

This tells me that maybe there is a parity problem with the algorithm. It only finds a solution for certain orientations of the line.

#4

Thank you your report. We will have to examine the algorithm.

#5

I upgraded to 2021.4, but am experiencing the same issues. I am attaching a script that shows highly variable behavior of this function for different straight lines and on translations.curves.cub (19.6 KB) arc3.jou (952 Bytes)