Question About Tangent Planes

[lil.ethereal.x]

Hiya

When constructing a plane tangent to a face, I can use the tangent plane tool under the construction tab fine on an even curve, but with a conic curve I first need to define the angle of the desired tangent plane in a sketch, then use the plane tangent to face at point as the tangent face comand just refuses to let me select the conic face. Attached is a screenshot that will hopely show what I'm talking about. On the left there is a surface extruded from a conic curve and on the right there is a surface extruded from an arc. The tangent plane on the arc is made using a tangent plane command and defining an angle of 45 degrees but the tangent plane on the left required me to make a sketch to define a line, 45 degrees from vertical and then use the plane tangent to face at point to create the desired construction plane.

Is this normal behaviour? I don't understand why I can't just use the tangent plane command on the conic surface. I have basically no understanding of how fusion works under the hood so implementing this may be far more work  than it's worth, I'm just curious if there's an answer I'm not seeing

Thanks,

Lil

[jhackney1972]

I think you can illustrate, what I believe, is the issue by adding a line to your left hand conic sketch.  The same reason the tangent plane will not work is also the reason the line will not constrain to the curve using a tangent.

[g-andresen]

Hi,

Here is another proof that the position of the tangent to the curve must be defined

günther

[lil.ethereal.x]

Hiya 

Sorry for the delay, life got onto of me.

Your explanation doesn't really help me understand what the problem actually is. All you've done is provided me with another example of fusion struggling with tangents on uneven curves and told me it's the same reason tangent planes don't work either.

The thing that's baffling me is that fusion doesn't actually struggle to find the gradient of the tangent plane. When constructing a plane tangent to face at point the only extra geometry fusion requires is the point at which the tangent plane should intersect with the conic surface. Fusion can calculate the gradient of the tangent plane  perfectly happily all it needs is the point to intersect the arc. I can't see any reason why fusion is making a fuss about it.

Thanks,

Lil

[lil.ethereal.x]

Hiya

I'm not looking for proof that tangent planes need to be defined I'm looking for an explanation as to why they need to be defined. The fact they need to be defined is the whole thing that I'm struggling to understand. The simple workaround is the one that I've shown in my original post and the one that you've shown in your video. I'm just curious why this is the case.

Thanks,

Lil

[g-andresen · Accepted solution]

Hi,

Because a tangent is a straight line that touches a curve at only one point, you must define that point.

günther

[lil.ethereal.x]

Hiya

When trying to make a tangent plane on an evenly curved surface I don't need to define the point where they touch just the angle at which the tangent plane will sit and when trying to use a tangent constraint in a sketch it fails even when an intersection point is defined.

I'm not sure there is an explanation that will satisfy my curiosity, oh well.

Thanks,

Lil

[lil.ethereal.x]

Hiya

When trying to make a tangent plane on an evenly curved surface I don't need to define the point where they touch just the angle at which the tangent plane will sit and when trying to use a tangent constraint in a sketch it fails even when an intersection point is defined.

I'm not sure there is an explanation that will satisfy my curiosity, oh well.

Thanks,
Lil

[g-andresen]

Hi,

In this screencast you can see that the planes on the right-hand body are determined both by the wave profile and by the tapering of this profile and that there can only be a tangential plane at one point.

For the left prismatic body, on the other hand, the tangential condition is given at the specified angle over the complete height.

günther