How do I create a plane that is perpendicular to a surface?

Kira_Lee · October 2021

I am trying to make a revolved cut feature that I can drop onto a cylinder face (the cylinder should be able to be anywhere in space) but the sketch plane has to be perpendicular to the face chosen.
I've used the code below where realPlane is the plane chosen by the user.

var sketchPlane1 = plane(vector(0, 0, 0) * inch, realPlane.origin);

but if my realPlane.origin happens to also be the world coordinate of 0, 0, 0 in space, this doesn't work.

For this feature, the length of the cylinder isn't fixed nor is it known in the feature - the only input/parameter is the face that's chosen.

Thanks in advance!

_anton · October 2021

If you have a planar face and you want to make *some* plane perpendicular to it, you can construct it with perpendicularVector(facePlane.normal) as the normal. https://cad.onshape.com/FsDoc/library.html#perpendicularVector-Vector

_anton · October 2021

If you have a planar face and you want to make *some* plane perpendicular to it, you can construct it with perpendicularVector(facePlane.normal) as the normal. https://cad.onshape.com/FsDoc/library.html#perpendicularVector-Vector

duncan_ledesma · December 2025

Testing using the TFR planes - perpendicularVector only works for Front "Cannot resolve plane". This is not a complete answer unfortunately.

Here is my file if you're curious. It attempts to make a sketch given a face and extrudes a cylinder. The relevant portion is three lines long and comprises two println sandwiching the plane.normal reassignment:

FeatureScript 2837;
import(path : "onshape/std/common.fs", version : "2837.0");

annotation { "Feature Type Name" : "Cylinder", "Feature Type Description" : "Make a cylinder in the middle of the plane" }
export const f3 = defineFeature(function(context is Context, id is Id, definition is map)
    precondition
    {
        // Define the parameters of the feature type
        annotation { "Name": "Face", "Filter": EntityType.FACE }
        definition.face is Query;
        annotation { "Name" : "Diameter" }
        isLength(definition.diameter, LENGTH_BOUNDS);
        annotation { "Name" : "Length" }
        isLength(definition.length, LENGTH_BOUNDS);
        
    }
    {
        
        // Assertion
        if (definition.diameter <= 0 || definition.length <= 0) throw regenError("Absolute values only");
        
        // Face -> Plane
        var plane = evPlane(
            context, 
            { "face" : definition.face }
        );
        
        println("Before: " ~ plane.normal);
        plane.normal = perpendicularVector(plane.normal);  // uncomment this line to use original behaviour
        println("After: " ~ plane.normal);
        
        // Plane -> Sketch
        var sketch = newSketchOnPlane(
            context, 
            id + "sketch", 
            { "sketchPlane" : plane }
        );
        
        // Sketch -> Add circle 
        skCircle(sketch, "circle", {
                "center" : vector(0, 0) * millimeter,
                "radius" : definition.diameter,
        });
        
        skSolve(sketch);
        
        var skr = qSketchRegion(id + "sketch");
        
        opExtrude(context, id + "extrude", {
            "entities" : skr,
            "direction" : evOwnerSketchPlane(context, {"entity" : skr}).normal,
            "startBound": BoundingType.BLIND,
            "startDepth": definition.length / 2,
            "endBound" : BoundingType.BLIND,
            "endDepth" : definition.length / 2
        });   
    });

If I learn of a solution that works for all test cases, I will come back to this thread.

NeilCooke · December 2025

You can't just change a plane's normal, you need to reconstruct it using plane(plane.origin, perpendicularVector(plane.normal))

duncan_ledesma · January 1

https://forum.onshape.com/discussion/comment/125001#Comment_125001

Replying to confirm that this solved my issue. I spent a shameful amount of time trying to fix it in other ways the other day, but it's obvious even to a non-mathematician.

How do I create a plane that is perpendicular to a surface?

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