Application of angled void-extrusion/cut not possible

[tbg4H7P3]

Hello,

I have a problem understanding the behaviour of Revit in a certain situation.

When I create a rectangular shaped solid and I want to cut it with a rectangular shaped void extrusion which is angled.

I face the same problem as described here: https://forums.autodesk.com/t5/revit-api-forum/application-of-void-extrusion-cut-not-possible-for-pr...

The created profile has a perfect aligned cut but to prevent problems (as in the link) when applying the cut the length of the profile is increased. Which leads to the new problem that depending on the angle in which the void extrusion is rotated, the length in which the profile should be increased needs to be bigger/smaller.

In the linked file (CutTestFamily.rfa) I created a test scenario and basically looked up values which I need.

Angle (degrees) of Void Extrusion	Length of Increasement
1	9.17mm
2	4.521mm
3	3.037mm
4	2.275mm
5	1.826mm
10	0.909mm
20	0.448mm
89	0.155mm

This leads to the formula 10/angle (10 to be a little bit bigger). To avoid being below the 1/32inch “Minimal Line Length” I implemented the following function.

        private double GetProfileDistanceByAngleInMillimeters(double angleInDegree)

        {

            const double maxLength = 10.0d; //mm estimated through testing

            var minAllowedLength = ConstructionConstraints.ProfileIncreasementLengthMillimeters; // 1/32 Inch in Millimeters

            return Math.Max(maxLength / angleInDegree, minAllowedLength);

        }

I do not understand how Revit is handling the calculation of the length. I really want to know the real Threshold that Revit is working with so I can have a solution that is always working, since this 10mm is just an estimated value here.

Best regards,

Tim B.

[jeremy_tammik]

Dear Tim,

I doubt that anyone knows.

I'm afraid you will have to continue experimenting and testing.

if you think the values can be calculated using a formula, I will gladly take a look at it. Is it just a 2D problem, and basically a triangle of sorts? Can you make a sketch of what length you are trying to calculate? Is there a reason why you don't want to make it significantly longer?

Why are you modelling such small things, at the limit of Revit's minimum precision? Are they relevant in the BIM?

[tbg4H7P3]

Hey Jeremy,

thank you for your quick reply.

---

Why are you modelling such small things, at the limit of Revit's minimum precision? Are they relevant in the BIM?

---

It is basically to get the best result possible, but the problem is that I automatically create bigger families and often i run into problem which are caused by unknown constraints/weird behaviours of Revit and those could be prevented by fully understand how Revit handles those thinks.

---

Is it just a 2D problem, and basically a triangle of sorts? Can you make a sketch of what length you are trying to calculate? Is there a reason why you don't want to make it significantly longer?

---

It is a 2D and 3D problem.  The reason why i dont want to make it unecessary longer is that the longer the distance gets the higher and wider the void extrusion gets. Since the sizes of the void extrusion are calculated.

Sketch of the problem:

the blueish line in the length that needs to be calculated to avoid the problems mentioned in: https://forums.autodesk.com/t5/revit-api-forum/application-of-void-extrusion-cut-not-possible-for-pr...

Best Regards,

Tim B.

[RPTHOMAS108]

In 2022 I was trying to replicate the usual error with the family you provided and these all seemed to cut (in the family environment).

What was odder still was that if the cut left an edge shorter than short curve tolerance then rather than the cut failing the problem edge would just disappear leaving two unconnected edges. Perhaps that different behaviour was due to family environment or different Revit version?

With respect to the original thread I don't understand why the extension should need to be greater depending on the angle of the cut. In the original thread the cutting plane either falls on the vertical edge in which case it leaves a tiny length of that edge or the horizontal edge where it cuts back the entire vertical edge. So I don't know if the problem here is the same exactly or the theory in the other thread was wrong?

Considering further there is uncertainty of the vertical and horizontal position of the corner being cut when looking at tiny numbers. So the shallow angles may cause the same problem of tiny edge on surface. I would have thought however that if the extension is greater than a significant amount then it should not be an issue.

If you are creating and placing the void with the API then you can reduce it's extent to suit a 10mm extension. However it seems like an awkward way of achieving the cut in reality anyway: If the profile of the solid being cut varies as you go into the screen then you'll likely experience other 3D cutting issues and if it doesn't then why not just extrude that final profile into the screen to start with? 

I found in the past also that cut faces are hard to dimension in the project.