topic Re: Sketched spline in 3D Part & Assembly Design

Sketched spline

GrahameWard — Sun, 13 Dec 2020 10:47:37 GMT

Can anyone explain to me what information I am leaving off this sketch?

The spline sketched below should be symmetrical, or more accurately, the ends should be as though they are rotated 180 degrees around the center, but they’re not. The little inset in the bottom right shows what it looks like when I mirror the sketch left/right then top/bottom. It should lie on top of the original but it doesn’t. The dimensions should make the thing symmetrical but don't.

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Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 14:58:48 GMT

For splines, there is position and angle but also the influence drag handle. You can mirror the position and make the angles the same, but making the influence drag handle symmetric is more difficult.

One way is to make half of your spline and then use copy > paste special on the sketch entity to create a dependant copy at 180 degrees. This has the advantage of leaving the spline drag handles "dragable" in your sketch.

Another way is to select your spline in the sketch, RMB and pick "modify" and on the spline dashboard pick the icon that shows the drag handle dimensioned. This requires you to fully dimension the spline, including the drag handles, however you can then make the drag handles equal and apply constraints like symmetric to the drag handle intersections.

Re: Sketched spline

Inoram — Tue, 28 Jan 2014 16:05:51 GMT

I rarely use splines, so sorry I don't have an answer, but I was trying to learn more about them. I drew this using the polygon control, but it still doesn't look 100% correct as there is a drag handle slightly off center and I'm not sure why.

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 16:19:50 GMT

Looks like you're missing an on entity constraint in the upper right to the line indicated.

Re: Sketched spline

Inoram — Tue, 28 Jan 2014 16:47:04 GMT

I thought that, too. but even changing it to this. It's still not right.

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 16:55:25 GMT

It's not immediately obvious to me where the problem is. It looks OK to me, have you tried rotating a copy to check symmetry?

Re: Sketched spline

Inoram — Tue, 28 Jan 2014 16:56:48 GMT

yes

Re: Sketched spline

Inoram — Tue, 28 Jan 2014 17:09:06 GMT

This is even drawing another spline and using the control polygon to put it in the same place.

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 18:11:15 GMT

I'm stumped, I assumed that locking down the control polygon would define the spline explicitly.

No time to play with it right now, I may be able later.

Re: Sketched spline

Inoram — Tue, 28 Jan 2014 18:15:50 GMT

Attached file if you want to look at it.

(Creo2)

Re: Sketched spline

GrahameWard — Tue, 28 Jan 2014 18:23:14 GMT

Well, I see you guys have a good hard look at it... but you're no closer to a solution than I am.

I see some of the screen shots have extra points added to the spline. That's what bugs me about this - it's a really simple spline. There are only 3 points to it, so the chances of something going wrong should be minimal. The one in the middle is where the 45 degree angle dimension is. The end points are the 60 degree angle dims and that's it, apart for the 20 and 2.5 x and y dimensions.

Doug, I am not able to get any drag handle. Matt, I cannot get polygon control. I click on that icon in the sketch but nothing happens. If I start it from scratch I can't get to the polygon.

I can only assume that ProE treats the start point different from the end point of the spline. It shouldn't. It's supposed to be parametric - the dimensions and constraints applied to the sketched geometry should give one predictable solution

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 19:14:27 GMT

Inside sketer, select the spline. Rickclick on it and select "Modify". In the spline dashboard that then appears you should be able to show the drag handles/polygons (same thing).

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 19:33:43 GMT

OK, took a quick look at this some more. In WF4, I could not get the dimensioned control polygon to show due to internal dimensions. In Creo 2, forcing the control polygon to display required the internal control point to be disconnected from the center. Evidently, if you are going to dimension the control polygon, you cannot constrain the internal points.

Splitting the spline into two splines seems to solve it, but it makes it more complicated to dimension.

Re: Sketched spline

TomD.inPDX — Tue, 28 Jan 2014 19:33:57 GMT

This one works fine... 3 points and edit with control polygons

Re: Sketched spline

dgschaefer — Tue, 28 Jan 2014 19:36:55 GMT

How were you able to get the internal point "on entity" while showing the control polygon?

Re: Sketched spline

TomD.inPDX — Tue, 28 Jan 2014 19:38:56 GMT

File attached.

Turn on the annotation and update at will.

Creo 2.0

Re: Sketched spline

TomD.inPDX — Tue, 28 Jan 2014 19:39:29 GMT

Mine didn't complain.

Re: Sketched spline

TomD.inPDX — Tue, 28 Jan 2014 20:07:57 GMT

I see what you mean... I dimensioned the control point prior to turning on the polygon control. This is one of those "sneak up on it" scenarios. I probably did it out of habit and didn't even realize the implications anymore.

steps: (note; my config.pro has edited dimensions as locked in sketcher)

3 point spline along horizontal on reference.

dimension center out on both sides and equal values (this is probably why it worked)

turn on polygon control and allow overwrite of strong "dimensions" (?) it didn't overwrite my locked dims.

constrain polygon segments as equal; ends/centers

remove horizontal constraints

add on-reference constraints at center node; vertical and horizontal

drag 1st and 3rd polygon points and dimension 30 degrees and 45 degrees

be sure linear dim 10 and 10 are locked

remove endpoint align constraint on reference

drag endpoint off the reference

dimension the vertical offset

constrain all like dimensions as equal

Re: Sketched spline

GrahameWard — Tue, 28 Jan 2014 20:10:15 GMT

I know how to get there, and I see the 'show polygon' icon, but nothing happens when I click on it.

Re: Sketched spline

GrahameWard — Tue, 28 Jan 2014 20:20:34 GMT

Okay, I think I did it. I stared the curve again, but did not put a point in the middle. With the polygon in place, I set the end segments of the polygon to be equal length, which, with the 30 degree dimension the same at each end means of course that the spline goes through the center without needing the point in the middle to constrain it.

This looks right, doesn't it?