topic Re: Tangent between two curves in Fusion Support Forum

Tangent between two curves

XDGFX — Thu, 20 Jun 2019 14:28:01 GMT

Hello,

I was using Fusion 360 last night and ran into an issue - I am unable to create a curve which is tangent between to curves. For reference, below is a screenshot from NX with what I want to achieve

Left: One curve is tangent to two other curves. Right: curve is NOT tangent to two other curves

No matter what I tried I wasn't able to select both inner and one of the outer curves when making a tangent selection. If I trimmed the outer curves to length, tangent was allowed but it would move the outer curves from the position they were in - and if I fixed the outer curves I was not allowed to select them for tangent!

This seems like something fairly basic that should be possible. In short; we should be able to make any curve tangent to any other curve or line, even if the ends of each curve are not coincident (see the example below)

Middle curve is not touching lower curve, however it is still tangent to it

Maybe I am just missing something, but if not this really should be added!

Betreff: Tangent between two curves

g-andresen — Thu, 20 Jun 2019 16:59:13 GMT

Hi,

Is it possible that any circular arc, between 2 other (fixed and certain) circular arcs, is spanned in such a way that it is tangential to both?

Circular arcs and their tangential condition

günther

Re: Tangent between two curves

HughesTooling — Thu, 20 Jun 2019 17:48:02 GMT

@XDGFX Can you export your problem design as an f3d and attach?

Mark

Re: Tangent between two curves

HughesTooling — Thu, 20 Jun 2019 17:51:18 GMT

Here's an example of an arc that's tangent to 2 more arcs and doesn't touch, so it is possible in Fusion.

Mark

Re: Tangent between two curves

etfrench — Thu, 20 Jun 2019 19:23:11 GMT

I'm not having any problems making 4 arcs tangent in any combination of having a large or small arc fixed. You may need to Fix/Unfix the arc which should not change position or size in order to create the tangent.

Re: Tangent between two curves

XDGFX — Fri, 21 Jun 2019 07:33:17 GMT

Interesting it does seem to be possible.

Attached is the .f3d - the latest sketch has a curve I am trying to make tangent.

Re: Tangent between two curves

HughesTooling — Fri, 21 Jun 2019 10:23:36 GMT

The reason it's not working is because Fusion can't add a tangent constraint to a point on a spline, you can only add tangency at endpoints.

Mark

Re: Tangent between two curves

HughesTooling — Fri, 21 Jun 2019 10:28:21 GMT

Note. The endpoint of the spline and arc need to be connected as well.

Mark

Re: Tangent between two curves

XDGFX — Fri, 21 Jun 2019 11:18:50 GMT

Ok, so it seems this is the problem.

I have trimmed the outer curves so I am adding tangent constraints to the end points. If I fix the two outer curves (as shown) the length is also fixed. I can create a tangent constraint on one side, but not on the other as the length needs to change.

If I don't fix one of the outer curves, I get the following:

The unfixed curve is no longer in the position I wanted it.

I need everything on the outer curve to be fixed, except the length can vary (alternatively I need to be able to create a tangent constraint to any point on the outer curve)

Does anyone have any ideas on how to get around this?

Re: Tangent between two curves

XDGFX — Fri, 21 Jun 2019 11:20:54 GMT

Further to my previous response, it kind of looks like you've constrained to any point along the outer curves - rather than the ends points.

How have you one this?

Re: Tangent between two curves

XDGFX — Fri, 21 Jun 2019 11:23:10 GMT

Aha...

It seems to be because in my case the two outer curves are splines - not simple arcs.

It would still be nice if a tangent constraint could be made but I understand now why there seems to be an issue with creating the constraint.