topic Re: 3D Spline Creating, Positioning & Joining Another Polyline Problem in AutoCAD Forum

3D Spline Creating, Positioning & Joining Another Polyline Problem

andyMZHMH — Tue, 01 Feb 2022 14:50:23 GMT

Truly hoping someone can help - this has been driving me nuts for a couple of days!

I have a glazed frame positioned correctly to suit the structure which is curved on plan.

The screen finishes slightly off the side of a curved CHS steel at the left hand side, and needs to follow the line of the CHS and then add a curve at the top corner before joining up with the top frame member - roughly as the yellow hand drawn line in the screen grab below. The glass/frame is vertical (and has to be), whereas the CHS is curved and kind of twisting.

I continued the screen well past it's intended final position, planning to create a Spline relative to the CHS, with the curve added formed into it and then join it to one of the red polylines for set up as "Frameline" across the top, then Sweep the head frame members down it. I'd then finish off by setting up some surfaces to Slice everything in and tidy it all up.

Can anybody please help by giving some guidance how I can form a 3D Spline, roughly following the CHS with a curve added in the top, which I would be able to Sweep the top frame member down and also keep it planar to the glass so it fits?

I hope I've explained ok what I've been trying to do - a screenshot is posted below and I've attached a DWG file - hopefully so someone might help with a suggestion. Thanks and fingers crossed.

Re: 3D Spline Creating, Positioning & Joining Another Polyline Problem

leeminardi — Tue, 01 Feb 2022 15:49:52 GMT

I'm not fully sure what you want to do but if it's to create a 3D spline from point A to B that has a slope tangent to a horizontal line at A, wraps around the curves wall and ends at B here is method to consider.

I'll assume A has a z value = 16210 so set the elevation to 16210 with osnap off.

Working in the top view (again with osnap off) create a spline using the fit point method and about 5 fit points to define a spline on the z = 16210 plane. After the last point specify T for tangent and provide a suitable tangent vector point. Although you can control a spline's tangent at the beginning of a spline with the "T" option I have found that it can yield strange results and therefore prefer to control tangency by moving the spline's second Control Vertex.

Now go to the back view and change the UCS to View and give the splinedit command (or spe) followed by E (edit) and M (move) cycle through the CVs (by repeatedly hitting the space bar) until you have the left most CV and with orthomode on drag the end CV down as shown below,

Once you have used splinedit to modify the location of a CV you can drag CVs without the use of splinedit. Still working in the back view continue to drag CVs down to form a smooth curve. To ensure that the spline's tangent at the top ends matches the straight line do not move the next to the end CV.

If this is not your goal please provide more information.

Re: 3D Spline Creating, Positioning & Joining Another Polyline Problem

andyMZHMH — Wed, 02 Feb 2022 01:28:26 GMT

Big thanks for your help - this is what I'm trying to achieve - once I get the spline in place I can easily Sweep and Slice and Trim to tidy it all up, but I just couldn't get it right. I'll give this a try now and let you know how it goes (or if it doesn't quite work out for some reason!)