Tangency and Perpendicularity to Spline at Point

[dtruong0131]

I would like to see the ability to add tangent and perpendicularity constraints to arbitrary points along splines. We can make geometry tangent and perpendicular to tangent handles on fit point splines, but we should be able to do this along the entire length, and control point splines offer no such luxury. There are roundabout ways to accomplish this, but they require leaving the sketch environment and using hacky surface modeling tricks to establish normal vectors.

[SaeedHamza]

This is an interesting topic, could you please elaborate more on how would you benefit from achieving such controls? an example would be very helpful.

Because you've mentioned "establish normal vectors", and that got my attention.

[etfrench]

Try this:

1. Offset spline.
2. Put arbitrary point coincident to spline.
3. Draw circle with center coincident to offset spline.
4. Add coincident constraint between circle and point.

Plane on path would be the most accurate method.

Actually, if you drag the circle, you'll find two valid solutions to the constraints.  Bisecting the angle should give an accurate line perpendicular to the plane at a point.  Note: The purple projected line is from a Plane on Path.

[dtruong0131]

There are ways to accomplish the task, but they all require more steps than should be necessary. This is an example of that.

[dtruong0131]

I don't have a particular use case for this at the moment, as I mostly avoid sketching splines whenever possible. I think I avoid them because it's annoying to constrain them, especially tangentially to circles or ellipses. I recall a project I was working on a couple of years ago where I was trying to do this, figured out a workaround, and went with that, but I was annoyed at how roundabout the solution had to be because tangency to a spline at a point and sketching lines normal to a spline at a point should be built-in as it is with arcs.

[MichaelT_123]

Hi Mr. Dtruong0131,  Fellows,

The theme "Tangency and Perpendicularity to Spline at Point" ... is popular on this Forum, like 'Dark Side of the Moon' by Pink Floyd. It is timeless.

There are many posts about the subject, including mine.

As for the future generations of Fusionates, and those unfortunate with geometrical dementia ...

A spline in 3D has one tangent line at a point and infinite normal lines perpendicular to it.

You will find some solutions here (and certainly in many other posts)

https://forums.autodesk.com/t5/fusion-360-design-validate/invincible-tangent-line/m-p/11828219

https://forums.autodesk.com/t5/fusion-360-design-validate/how-to-constrain-a-line-so-that-it-is-norm...

Some time ago, I have started another educational video/post on the subject. Unfortunately (or not), I abandoned it in part due to the difficulty in how F360 handles ellipse-spline-userParameters interplay. In this sense, I agree with the post's author... but for the vast majority of F360 users ... there are solutions to the problem.

Regards

MichaelT

[dtruong0131]

I understand how to sketch a tangent line to a spline at a point and how to create a line normal to the spline at a point, but I believe it shouldn't require a roundabout solution; it should be akin to the handling of arcs. I appreciate your reply, though.