10 Replies Latest reply on Oct 17, 2017 10:16 AM by Matt Lombard

# Why can't I measure the angle between two flat surfaces?

Straightforward question, but nothing on the forum about it with a quick search. Why is it that I can measure the angle between two solid faces, but I can't between two surfaces? They are 'fill' faces, but they are flat.

Solid Faces;

Surfaces;

• ###### Re: Why can't I measure the angle between two flat surfaces?

If you know that they are flat, why are you using Fill instead of Planar Surface?

• ###### Re: Why can't I measure the angle between two flat surfaces?

Because I was making an odd shape within constraints, and converting a 3D sketch into a representation of surfaces I could make an assembly within.

• ###### Re: Why can't I measure the angle between two flat surfaces?

I'm no expert in surfacing but I'm guessing the Fill surfaces aren't truly flat.

Use the Zebra shading for a quick check

• ###### Re: Why can't I measure the angle between two flat surfaces?

I think that was it. There is a tiny amount of distortion, even though the square I used to make the surface was perfectly perpendicular.

• ###### Re: Why can't I measure the angle between two flat surfaces?

When you use surface-fill feature, the result will be a composite curve which can be tangent or curvature to others while surface flat feature will provide you a flat surface as Jim mentioned - see att. file

• ###### Re: Why can't I measure the angle between two flat surfaces?

I'm late to this, but just wanted to add some ideas. A quick check for planar surface is if you can open a sketch on it. That will tell you immediately.

The whole thing about angles between planes is much more complicated than it seems. You can only truly measure an angle between lines. You can't measure between planes. When you think you're measuring between planes, you're actually trying to measure the maximum angle between the planes. If the measurement is angled, the measured angle will change. So you have to specify where you want to measure the angle with another plane, or with two lines. If you just ask SolidWorks to measure between two planes, it's going to give you what it thinks you are asking for, which is not guaranteed to be what you are actually asking for. It might be measuring between the plane normals, or between the U-V curves, or the maximum angle, you don't really know. You need to specify measurements like that more clearly. I would create another plane, and then create intersection curves and measure the angle between the curves.

Look at the picture below. All of the angles are between Plane1 and FrontXY. When you ask SW with the Measure command, it gives you 67 deg, which is the max angle that can be measured. But all of the angles are valid. This is why I'm always careful when specifying angles between faces, because that implies that you are measuring the maximum angle, which might be obvious or not.

• ###### Re: Why can't I measure the angle between two flat surfaces?

Welcome back Matt.

• ###### Re: Why can't I measure the angle between two flat surfaces?

Matt Lombard wrote:

If you just ask SolidWorks to measure between two planes, it's going to give you what it thinks you are asking for, which is not guaranteed to be what you are actually asking for. It might be measuring between the plane normals, or between the U-V curves, or the maximum angle, you don't really know.

Hi Matt,

Welcome back.

Measuring between planes in SOLIDWORKS measures the angle between the plane normals (which is really equivalent to the maximum angle as shown in your example) so it should always be consistent. But, certainly measuring between a plane and lines/edges or betwen two lines/edges is easier to visualize for users so is a good suggestion if there are lines/edges that can be used for the specific situation.

Thanks,

Jim

• ###### Re: Why can't I measure the angle between two flat surfaces?

Yes, welcome back Matt.

Steve C

• ###### Re: Why can't I measure the angle between two flat surfaces?

Thanks guys.