Extrude "cone" along followme path


#1

Hi guys,
Struggling to work out how to sketch the two “connecting pipes” along the paths shown in yellow, where the pipe diameter progresses from small to large along its length.
Can anyone help?


#2

You basically need a plugin for that, it can be done manually but it takes some explanation.
Fredo6’s Curviloft middle button will do it for you in a few clicks.


#3

Thanks Box.
Now that I’ve asked that, can you help me “create” the yellow paths in the firs place? I created them on this screenshot in photoshop as I am struggling to get all lines and arcs aligned to cnetrepoints etc. Maybe I’m usiong the wrong kind of arc tool. Maybe a bezier line tool might help.


#4

Fredo has a bezier tool too. Install that as well and away you go.
On phone only for a few days so can’t make any demos.


#5

Okay, I’m gtting pretty close here I think. Took me all day!

So the problem I have now is the distribution of the vertices after using loft along path.

You can see that the “top” half of the model is fine, with vertices evenly distributed evenly along the curved circumference. The bottom face, however, has vertices “bunched up” in some areas, and more spaced out in others. I’ve managed to align connections between the the vertices, but I can’t seem to make them space evenly as with the top face and middle faces.
This is distorting my model slightly, and causes problems with wall thickness .


#6

I’ve only used Curviloft once or twice, but as I recall the distribution of intermediate “crossing” edges is directly derived from the edges forming the path to be lofted. Does your S-shaped path (from one end of the shape to the other) consist of edge segments that are approximately equal in length?

Edited to add: in case the concern is with points that are unevenly distributed about the semi-circular periphery of the flat near-end of the shape, that would also depend on how that shape’s peripheral edge segments are laid out (prior to using Curiloft).


#7

Yes TDahl. That’s exactly my issue. All three “faces” I’ve used are derived from circles, with the top two having vertices spaced evenly. The highlighted area seems to be more tightly packed than the area immediately to the right.

Capture


#8

I would assume that the flat face originally created to represent that end of the 3D shape has those uneven edge segment lengths build into it.

As an experiment, try using Push-Pull to extrude that flat end out a little ways, and then look at the facets that are created by Push-Pull (you might need to turn on display of Hidden objects to clearly see the individual facets). If the facets along the arcs have uneven widths, then those arcs have uneven edge lengths for some reason.

How was the near-end profile constructed? You wrote they were derived from circles, but I’m wondering what kind of actions might have broken some of the circumferential edges into two segments, for example. Drawing a new line (edge) that touches one of the existing edge segments will do it.


#9

That’ll be it I guess. both “protrusions” from the circle were drawn with freehand lines. Is there a good way to get a circle with protrusions like that and maintain even distribution of the vertices along the curved surface?


#10

Try to weld those edges, I’m not sure if it’s going to help but worth a try…


#11

will do! thanks


#12

Is the near (small) end of the 3D shape intended to be a scaled-down version of the far end of the shape? If so then I would use SketchUp’s Scale tool to shrink a copy of the far-end profile to create the near-end profile.

If the two ends are not scaled versions of each other, here’s what I would probably do, though it’s more involved than perhaps necessary. It involves the Circle Intersect extension (can’t recall where I got it, Extension Warehouse or Sketchucation shop).

  1. Draw the tapered “bar” that extends from far-left to far-right.

  2. Draw a partial arc (say 20 degrees of extent, doesn’t matter exactly) that corresponds to the outside-diameter circle; put this temporary partial arc above or below the bar and don’t let it touch the bar. To draw this and the next two arcs, use the Arc tool that lets you begin at the arc center-point (on a Mac the keyboard shortcut for this form of Arc is Command-J). You can numerically specify the exact radius of the arc, which is very handy. After clicking on the center point and moving the mouse away, just type the radius dimension and press Enter. Then move the mouse to sweep the arc a bit and click to finish it.

  3. Use the Circle Intersect extension to find the exact points where that partial arc intersects the top edge of the tapered bar, and then the bottom edge of the tapered bar. The extension will add construction points at the locations of exact intersection.

  4. Delete the partial arc, and now draw the final arcs from one construction-point to the other along the top edge, and then the bottom edge, of the tapered bar. Delete the line segments of the bar that span the interior of the circular area. Set the number of segments in the top and bottom arcs to be as desired (you can change this after drawing them but before running Curviloft via the Entity Info window).

  5. Finally draw the inside-diameter circle.

In this manner the upper and lower arcs will consist of exactly-equal length segments.


#14

Thanks guys. The ends are not “quite” scaled versions of eachother. The circle is smaller, and the protrusions extend by different amounts at each end. The wall thickness is a consistent size (so is a higher relative thickness to the smaller circle). Will Joint Push-Pull work with dissimilar shapes - certainly looks interesting.

As a side point, I need to retain a circular X-section throughout, so as not to narrow the flowpath, which can be caused by the lateral “skew” of the stack, turning the X-section into an ellipse. I’ve done this by inserting an inclined intermediate plane on the curvloft extrusion path (shown in red above). Again, not sure whether JointPushPull can do this too.


#15

Are they the same taper angle top and bottom?


#16

Not necessarily. They’re free-drawn with the line tool - by eye.


#17

Circle Intersect is one of mine. Look at my id on the sketchucation plugin store.


#18

Thank you Steve @slbaumgartner for that extension - it is very handy! I like to be precise and your extension makes it possible. Sorry that I forgot from which site I had obtained it. :slight_smile:


#19

I redrew the ends so they are accurate. Much better now. Still can’t work out how to keep the “loft-section” perpendicular to the path along its whole length though. For some reason, it seems to remain completely horizontal throughout, making my circular cross section elliptical in the middle of the loft.


#20

And the result isn’t a solid group either, which means I can’t union it with the end plates. Might there be someone who can take a look for me and let me know where I’m going wrong?

Too big to post here, so link is at:
http://www.guycarnegie.com/DCOE_GT6.skp


#21

Bluephoto says
For some reason, it seems to remain completely horizontal throughout, making my circular cross section elliptical in the middle of the loft.

To avoid the ‘elliptic’ flattening section, you should use the method “offset along contour”, which is the button on the left. This is not the default however.

Option%20Offset%20Curviloft

Fredo