1-Visitor

Question

Sketched spline

Forum|Forum|12 years ago
January 28, 2014
5 replies
15170 views

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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General

D

dgschaefer

21-Topaz II

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.

I

Inoram

14-Alexandrite

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.

D

dgschaefer

21-Topaz II

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

I

Inoram

14-Alexandrite

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

G

GrahameWard

Author

1-Visitor

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

D

dgschaefer

21-Topaz II

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).

T

TomD.inPDX

17-Peridot

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

T

TomD.inPDX

17-Peridot

It is obvious we need a little more control of splines in sketches.

Anyone with maintenance... please vote for this:

Node Control of Spline in sketch

P

Peter1

1-Visitor

I have voted for this!

We have an issue with splines where we use 2 splines with control polygons, one at each end of the part. Sometimes the splines are different shapes, but sometimes they are the same. If we dimension both splines with the same values, and then you do a mirror or output to Autocad and mirror you will see clearly they are not exactly the same geometry. PTC says there is just a lot of math behind the spline function....and the user can't control all of it. For us, the only work around is to sketch 1 spline and then mirror, but that messes up the model when you want different geometries....fun!

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TomD.inPDX

17-Peridot

I find splines to be very unreliable and extremely limited in sketches or as datum curves.

The fact that there is indeed a lot of math behind the spline, the control of that math should be put in the hands of the users. The current offerings are simply antiquated. Here is hoping Creo 3.0 will address this with some significant improvements.

The findings revealed in this discussion should be helpful if you have the patience to implement them and teach users the implications of those control points (nodes on the spline).

G

GrahameWard

Author

1-Visitor

This is totally bizarre. When I do this sketch again I cannot reproduce the same problem. It's now perfectly rotationally symmetrical like I want.