Symmetrical?

Those sketcher splines are tricky little buggers ~ you pull its little finger and it eyes cross. Something on the left side is a little off and it throws off the right side too. You'd think, also, that putting more points in would make it more even, but it just makes the waviness smaller, reduces the deviation from circularity. You can put 16 or a 100 points around in a circular pattern, connect them all with a spline, but never get a circle out of it.

One of the things you can do back in sketcher to check what shape you DO have is to double click the spline to get the spline modification interface. If you're using 2001 or later rev, there should be an icon that looks a little like a tape worm. This turns on the curve analysis function. Adjust the scale so that the normals are big enough to see clearly and adjust the density so that the connecting curve at the end of the normals is a smooth, stable shape. If anything is obviously wrong (asymetrical) about the spline, the analysis should show it.

If nothing obvious shows up, start zooming in on points and coincident attachments to make sure everything is rigged properly. Check dimensions, angles or whatever is providing the symmetry. If it needs still more help, try putting horizontal centerlines through the top and bottom points. One of the problems closed splines can have is one end leading and the other following its curvature and nothing independent for either end to be tangent to (although, this seems to have been straightened out in Wildfire's sketched splines). If you can't get either end constrained tangent, try deleting the spline and putting in the centerlines through those top and bottom points first, then doing the spline. Also, you may be able to place a dimensions to the horizontal centerline in place of tangency. Check again with curve analysis to see if it made any obvious difference.

Personally, though, I prefer creating curves through points where you have some definite control over start and end point tangency. This curve could also be 'traced' in sketcher or in a half dozen ways for creating surfaces which can later be turned into solids or 'thickened' instead of shelling a solid.

David Janes

Thanks for your detailed response. Mine are interspersed.

Oh, I knew that. I started with the spline having fewer points, and I added them very reluctantly to get up to 16.

I tried that before (if you mean "display curvature"), and yes, the display shows the sketch to be asymmetrical.

All points except the ones actually on the centre line have symmetry constraints.

I tried putting in centrelines. They go through the point, but I can't add a tangency constraint to the spline. I also can't put a dimension to the spline (click on spline, point, line) to control its tangency.

I really don't want to delete the spline and start again because there's too much redefining to do after so I will probably cut it in half and mirror it. That sounds silly but it will do.

Your latter point about the curve through points is a good one. I think I will try it with another part that is giving me the same problems but has fewer features coming after.

You're a very prolific poster!

: > If nothing obvious shows up, start zooming in on points and coincident attachments : > to make sure everything is rigged properly. Check dimensions, angles or whatever : : All points except the ones actually on the centre line have symmetry : constraints. : You may have misunderstood what I was driving at. When you've set up your framework in sketcher (datums, centerlines, points), you've created a lot of things that the spline can adhere to based on Intent Manager's auto constrain and snapping to references. So, even while your points are symmetrical, your spline may not be directly attached to the points. I was suggesting zooming in to check the attachment of the spline to the individual points. It would take only one that was misconstrained to throw your spline off the little bit that it was. Unexpected dimensions are a hint of this.

The procedure I use with splines eliminates this possibility and ensures symmetrical splines based on symmetrical points. This procedure is like turning off intent manager but with keeping the normal menus:

• Remove most features, especially the points you wish to anchor to, from the references. A lot of points as sketcher references really bogs down Pro/e's variable solver. I've done it, for example, with a lot of center lines for construction purposes. You need only the normal datums.

• Create the spline away from the points, clicking and creating a control point for each of the sketcher points and leaving the spline open. Don't let the start and end points attach to each other or any other reference.

• Use the constraints menu or toolbox to manually constrain spline control points to sketcher points with coincident constraints.

• Use the coincident constraint to attach start point to end point. The beginning and end segments should now be curvature continuous. Then constrain this combined point coincident with the top sketcher point. You need the horizontal centerlines, really, only when you do half, then mirror the feature or sketched spline. I just tried this with four symmetrical points and a closed sketcher spline curve. The spline came out perfectly symmetrical. You couldn't tell where the start/end was.

David Janes

P.S. You can find The Guttenberg Projects collection of Samuel Clemens works on their website, free for download. It's a 15 meg file when unzipped. That's what I call prolific. I guess I might be considered prolific, by NG standards, where one word or two sentence answers are more typical than complete ones, even when the question deserves more.

Thanks again for the advice. I've moved on from that job and did a work around by cutting the thing in half and mirroring it. It future I will try it the way you suggested. On this occasion though, I didn't get around to using datum points to attach the spline points to, I just had dimensions to the spline points themselves. The only references I had were the 2 default datums in edge view. I always keep my refs to the bare minimum necessary; I remove default ones if they're not needed by my sketch.