# Rhino Question

Discussion in 'Software' started by Mat-C, Nov 29, 2010.

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### Mat-CSenior Member

Can someone tell the simplest way to run one object along the edge of a surface in such a way so the surfaces are tangent to one another...?

So, for instance in the image below, say the two triangular surfaces are windscreen panels and I want to make up a frame from the box section, what would be the easiest way to do this..?

Apologies if the question isn't very clear... given the difficulty I've had explaining it, you can imagine the trouble I've had doing it!

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### vinceUKJunior Member

Hi MAT-C,

I guess by duplicating the edge curve from the rectangular box, moving this cruve to one side of the winscreen edge and by using the "Sweep1" shortcut that is the sweep 1 rail function.

Hope this helps, Vince

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### Mat-CSenior Member

Thanks Vince
Yep - tried that - but how do you ensure that the curve is lying perpendicular to the surface and its edge?

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### vinceUKJunior Member

If your rail lies on a XY plan, then by sweeping a curve that lies on a XZ plan you are sure to be perpendicular. And even if the rail "turns", it will remain perpendicular.

OK?

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### Mat-CSenior Member

Well... no... not really...
The surface lies on a 3 dimensional plane - XYZ, if you like. Once the Edge curve of the box section (or other shape) is lying perpendicular to both the surface edge and the surface itself, then yes, the sweep 1 rail will work fine.
It's how to align the edge curve in the 1st place that has me stumped....

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### DCockeySenior Member

Move a construction plane in one of the viewports so it's perpendicular to the curve. Right-click on the viewport name in the upper left corner of a viewport and a menu will drop down. Select "Set CPlane", then select "Perpendicular to Curve", then follow the instructions to set the CPlane at the desired point perpendicular to the desired curve.

Position the edge curve on the CPlane.
Sweep1

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### marshmatSenior Member

I tend to do cases like this as follows:
move: box so that one corner is in place
rotate: box, about the corner you just aligned, first ref is X-axis, 2nd ref is the other end of the target edge
rotate: same as before, in the other orthogonal view
rotate3d: axis is the target edge, 1st ref is an end edge of the extrusion being rotated, 2nd ref is a point on the windshield

It's not as clunky as it sounds... at least with good keyboard shortcuts and a 3dconnexion motion controller, it's about a 7-second procedure.

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### Mat-CSenior Member

Hmm.... ok - thanks again.
I've been doing it much like Matt described... with two roatate commands in 2 views, then extrude the rectangle / whatever to desried length.
Not clear about what the rotate3D step is for? Doesn't the other two rotations bring it into line?

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### rawSenior Member

Offset the surface a nominal distance then use the two edges in a sweep 2 command? then delete the offsett surface.

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### MikeJohnsSenior Member

________Surface
______________Extrude curve
__________________________Normal to surface

The nice folks at rhino wrote that code just to make life easy.

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### bhnautikaSenior Member

And now for something completely different. Draw a line back along a profile line (1) from the corner using the near snap or a copy of the line, then move it to the end corner. This continuation of the line can act as a base line to build the shape you want (2). Then taking a copy of the top edge line add it to the top corner (3), you now have the shape you want and the two rails to extrude along (4) which will give you more control of twist. If you have a surface that has variable slope over its length you can use the “split “ command to divide the surface into two pieces. Just make sure your cutting line goes through three points (two end and mid) if the surface is curved.

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### VisaVNew Member

Here's how I would do it.
1. Orient 3 points moves the section curve in place (does the same thing as Matt's rotations).
2. Sweep 1 rail along the windscreen edge. When picking the rail curve, click the ChainEdges option in the command line if your rail is in multiple pieces.

The frame should keep tangent to the windscreen. If it doesn't, use Offset curve on surface to make another rail and use sweep 2 rails.

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### bhnautikaSenior Member

Here is a another possible, using the extrude straight command select the top edge then type the letter D for direction, pick the two points that are on the same slope or plane of the direction you want to go (1). Then type in the figure for the distance; make sure the curser is on the side of the object you want to extrude two. Then repeat with the two side edges (2). Then fill in the last side however you like (3)

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