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Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

The end points don't start out with the end points coincident... That's after the tangency is established.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Nope, it overwrites the tangency with the lines and creates a tangent to itself. When you later divide the spline, the tangency to the construction lines reverts back

See if this video covers it.

Video Link : 4794

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

To answer the original problem - now read clearly. The question is how to make the datum-curve-through-points so that it is closed and has tangency continuity. I'd suggest repeating points, 10 or 20 if they are close together, to overlap the curve and then create a second curve that is trimmed to just one lap of the first curve.

***

1) Don't make the points coincident in Sketcher Intent Mangler. Change the coordinates after the feature is created, outside of Sketcher. Maybe it's possible to turn off the correct combination of automatic choices that are being made that interfere with the user intent.

1a) As an aside, this is one of the reasons I miss the old Sketcher. Intent Mangler just takes second guessing, backseat driving, control freak operations to an irritating level. I hope Intent Mangler can't create new constraints as part of regen outside of Sketcher. The UI group at PTC has a new feature. When the sketch is being worked on, an on-screen window showing all the automatic constraints is displayed with a check box to show the ones that are active and a counter next to each one to show how many of those constraints are currently used so the user can both easily toggle them on and off and see that expected constraints are used and if any unexpected constraints happen. Plus, clicking on each constraint that is used, active or not, causes the affected entities on the screen to flash. An up/down arrow allows the user to step though the constrained entities. A similar box also tracks the sketched entities so that one can step through the entities to help find those pesky open-loop causes. April Fools.

2) I tried to follow the video. Does Screencast-o-matic allow capturing from more than one app at a time? Maybe use Notepad to create instructions for each step and display them. It might also be more clear with just 3 points.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

This Mangler option sounds awesome.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Yes, it can capture whatever you select of the whole screen.

It was a quick video and it probably doesn't get the full impact of what I am trying to show.

I am not sure what happens if you make the connection outside the sketcher by "moving" those tangent reference lines. Somehow, I suspect it will still cause the spline to close and remove the tangents to the lines (makes it tangent to itself). This may not be an intent manager problem, however. in the video, I specifically made the ends of the spline tangent to the reference lines. Once the spline closed, it no longer had "ends".

Matt, I haven't tried a "by points" spline to see if it will close, but curves by equations do.

Once Paul gets back to this, we'll see what else we can uncover.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

No sweat - it's better than my videos.

In the days before Intent Manager it was often a challenge when nearly vertical or horizontal line segments were required. One would have to exaggerate the slopes to get the correct constraints and then change the dimensions to the desired ones. The bad news was that if there was a need to revisit the sketch, if one didn't re-exaggerate the values, Sketcher would re-evaluate the sketch and force the undesired constraints on the items.

The stupid thing was that Sketcher wasn't looking at the slope to determine the need to force the constraint, but at the apparent screen coordinate offsets, so if one zoomed in far enough the apparent offsets would increase and over-ride the automatic horizontal/vertical constraint.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Wait till you give this a try for yourself, David Splines are pretty dumb in Creo.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Edit, Matt- I can make the ends of a datum curve through points normal to a plane but not to itself. So you could have a tangency, but it is not defined that way. Datum curve through points definitely acts differently than the sketch spline. They don't even overlay the same.

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Well, thanks everyone, I think I have the answer.

it seems that in order for the datum curve-through points to be tangent to its start/end point, I actually have to specify the extra entities - a plane that curve is normal to, or a line that it's tangent to, or extra points that you then form straight-line segments.

I think what's missing here is a "this is a closed curve" checkbox.

But the behaviour I'm looking for is actually what the sketcher-mangler gives me - when I connect the end point of the spline to the start-point, the spline closes and is tangent to itself - and the tangent direction is determined automatically - probably by solving something like eq.19 from http://mathworld.wolfram.com/CubicSpline.html. Though who knows what kind of a spline creo actually uses?

And I found an easy way to do this if you have a lot of data points:

1) open a new sketch.

2) define a coordinate system

3) sketch a closed spline - 4 points will do

4) edit this spline - under the file tab, select the coordinate system, then import your points from a text file (*.PTS data file)

It is a bit baffling why you can't specify the spline points from the file when you are creating the spline in the first place, but oh well...

Paul

Re: Can you make a closed and tangent-to-itself datum curve in Creo 2.0?

Yes, the closed sketch spline want to go tangent to itself. You know that is the most natural curve.

As Dale points out, however, a datum curve will not close the same way. That one you have to trick into "closed tangency" with the -tails-.

I think forcing splines to be open or closed with an option is a great idea. Maybe you can recommend that in the Ideas section.