Bug? Coincident constraint not working on endpoint of offset line

[GRSnyder]

Take a look at the attached file. Your mission is to make the lower endpoint of the arc coincident with the right endpoint of the lower (offset) line by applying a coincident constraint.

It initially seems to work. But in fact, the arc endpoint ends up constrained to the lower line, not to the endpoint of the line. To see this you can either select the coincident constraint and see the entire line highlight, or you can drag the construction line up and down to demonstrate that the arc endpoint is easily separated from the end of the line.

This is consistently reproducible.

[jhackney1972]

It sounds like you are dragging the arc endpoint to the lower line endpoint using your mouse.  If you use the Coincident sketch constrain instead, and pick the end point of the arc and the endpoint of the lower line, it will joint the arc and the lower line, as it should.  You will not be able to separate them by dragging anything.  It will not add a tangent automatically however.

[GRSnyder]

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@jhackney1972 wrote: It sounds like you are dragging the arc endpoint to the lower line endpoint using your mouse.

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I've tried every option I'm aware of for adding that constraint: dragging the points together, activating the Coincident tool and selecting points in either order, and selecting points and then activating Coincident. For me, they all produce the same result.

Have you actually downloaded the file and tried it?

[g-andresen]

Hi,

works as described by   @jhackney1972  r

günther

[jhackney1972]

Yes I downloaded my model and tried a couple of methods.  As far as I could tell the Coincident function is working correctly. 

[TheCADWhisperer]

@GRSnyder 

Why do all of this extra work rather than simply use Sketch Slot command?

[TheCADWhisperer]

@jhackney1972 @g-andresen 

Did you really try it?

[HughesTooling]

Works for me, can select the pints in either order. The in on a PC with Win 10.

Edit OK should have read the original post a bit more carefully. Yes after adding the constraint you can drag it apart. Looks like the end point of the arc ends up only constrained to the line, not the end point.

[jhackney1972]

Error, see following post.

[jhackney1972]

Yes, I always test a supplied problem before posting a reply.  I did not see any issues with his model and the Coincident worked normally.  I am working on a Windows 10 laptop.

[TheCADWhisperer]

@jhackney1972 

Attach your solution file here.

Three users in this thread have reproduced this reported issue from the original file.

Two users in this thread have reported no issue but have not Attached proof.

[jhackney1972]

Attached in my file.  I see no issue if I also add a Coincident constraint to the center of the circle and the construction line which would be a normal practice in this model.  If you do not add this, you can separate the entities due to the center of the circle moving but the coincident stays intact on the one plane.

[TheCADWhisperer]

Redundant constraints should not be needed.

The point of the original post is that the points are not coincident constrained.

Dragging shows a point-line coincident “solution” not point-to-point as made with the selections. And if then try to add the coincident between points again Fusion reports that it already exists.

Looks like a bug in the sketch solver to me.

[GRSnyder]

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@g-andresen wrote: Hi, works as described by   @jhackney1972  r

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 Does it? You did not check to see if it applied the correct constraint as described in the OP.

[GRSnyder]

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@jhackney1972 wrote: I see no issue if I also add a Coincident constraint...
@TheCADWhisperer wrote: Redundant constraints should not be needed.

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Agreed. Should it not in fact be impossible to apply the extra constraint (arc center to construction line) because the model is already fully constrained? (Just to be clear, you can add that constraint in this test file, but only because the rest of the sketch isn't fully constrained and the original constraint isn't working correctly.) An arc with two fixed endpoints and a tangency constraint at one end is already fully constrained.

I don't think the problem is with the behavior of constraints. The problem is that the wrong constraint is being applied by the UI. The arc endpoint ends up constrained to the bottom line, not the bottom line's endpoint.

Here's an example where the lines are Fixed and not Offset. The arc endpoint constraint is correctly applied and the arc turns black because it's fully constrained. You cannot then constrain the arc center to the middle line. If you try, Fusion 360 just says "the sketch is overconstrained." (Just to be clear, this is an example of what I would claim is correct behavior. The arc endpoint ends up constrained to the line endpoint, and then the arc is fully constrained. If you just draw two parallel lines, it also works correctly. It's only (as far as I know) in the case of Offset lines that it starts to misbehave.)

[GRSnyder]

A couple of people have asked, "Why aren't you just using the Slot command?" The answer is that this is a bug report, not a how-do-I post. This is a test case simplified to demonstrate the bug with as little extraneous material as possible.

That said, in the actual application, the centerline of the slot is a spline. If anyone knows a better way of constructing a spline-shaped slot (that is, better than offsetting twice and adding end arcs), I would in fact be interested in that.

[HughesTooling]

@GRSnyder Although I agree this is a bug, how are you actually creating the arc? I tried a using a 3 point arc and just using the line tool and click, hold and drag and both of these methods create a joined arc. Worked on your simple example and with offset splines. File's attached.

[TheCADWhisperer]

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@jhackney1972 wrote:

...constraint to the center of the circle and the construction line which would be a normal practice in this model.  

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@jhackney1972 

In this similar example (two parallel lines) I don't have to constraint the center of the circle.

Merely add the Coincident between points as in the original problem description...

[jeff_strater]

I came to the same conclusion as @HughesTooling.  While the original situation certainly looks like a bug, there are ways to get the desired result.  3 Point Arc seemed to work for me, as well.

[GRSnyder]

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@HughesTooling wrote: Although I agree this is a bug, how are you actually creating the arc? I tried a using a 3 point arc and just using the line tool and click, hold and drag and both of these methods create a joined arc.

Those work for me, too. I had originally been adding center-point circles at the ends of the midline (with one of the offset endpoints as the point-on-circle) and trimming away the half I didn't want. Oddly enough, that picked up both coincident constraints and one tangent constraint.