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Set alignment point for lofting
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* May 20, 2017, 07:25:34 PM
Hi,

I'm trying to loft two 2D profiles ( ribs for a plane, root rib larger than tip rib ). When I do the loft, the leading edge of the small rib morphs int to top surface of the large rib.

Is there a way to set connection/alignment points when doing a loft so that I can get the leading edge of the small rib to loft into the same point on the large rib?

Thanks

Joel

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* May 21, 2017, 03:29:16 AM
#1
Can you post the 2D profiles for testing,   My first thoughts would be that the profiles don't have the same number of nodes, or the nodes are out of alignment.

When doing lofts like that it helps to draw the most complicated profile first (most number of nodes - which ideally should be the minimum required), then make copy of that into the other positions, and adjust (not adding nor deleting) the nodes as required, ensuring that any nodes at sharper areas are the same node from profile to profile. 

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* May 22, 2017, 06:18:16 PM
#2
This is set up ready to loft, the corners should all connect but they don't. You will see the front of the smaller ribs lofts into the top surface of the larger. The back end is fine. Does not matter which rib is selected first.

Thanks
Joel

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* May 22, 2017, 07:18:13 PM
#3
The profiles are Polylines with way too many nodes for optimal lofting. You should redraw them, following Andy's advised procedure. If you are using a Pro edition of TCad, then I'd suggest that you draw each profile as two Splines and two Lines, and loft with "Use compound profile" enabled. In Deluxe, I'd draw each profile as a single closed Spline with rounded ends, and then 3D-Slice the finished loft to achieve the flattened nose and tail. (See the attached screenshot.)

Henry H

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* May 23, 2017, 07:04:45 AM
#4
Thanks Henry and Andy, I will give it a try.

The reason I ended up the way I did, is that using spline by control points seemed the easiest way to trace the ribs.

Joel

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* May 23, 2017, 08:23:23 AM
#5
Thanks Henry and Andy, I will give it a try.

The reason I ended up the way I did, is that using spline by control points seemed the easiest way to trace the ribs.

Joel

"Spline by Control Points" is a good choice. Resist the temptation to use a great many points when drawing the curve; edit as required after drawing it. But the profiles in the drawing you posted are Polylines, which suggests that you had exploded the original curves.

Henry H

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* May 23, 2017, 10:22:04 AM
#6
Joel,  just to add if you happen to use the Join Polyline tool on a spline, it will convert it to a polyline, best to avoid doing it.

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* May 23, 2017, 06:41:33 PM
#7
Join polyline is what I was doing. I would draw the top spline, the bottom spline, and then lines on each end. To make them a single object I used join polyline. I looked for a "group selection" but could not find one. Is there another way to join the four objects into one?
It now lofts OK but it loses the curves, they become line segments so the curves are point to point line sements. Is there a setting somewhere to maintain the curves?

What I'm trying to do is only trace the tip and root ribs, loft between them, then slice at various points to get all the rib profiles in between.

Thanks

Joel

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* May 23, 2017, 07:11:21 PM
#8
To create a group there is a create group under the format menu in version 2016.  SEKE  Shift-Alt-G
Though, to loft them afterwards you will need to explode the group one time.

Facets see the two arrows in the png.  Setting will depend on your system and how slow you are willing to tolerate.  Also, uncheck degenerative faceting, though snaps don't all work on 3D objects.

There is also the expert parameters but I've not used them.

I found that if you  bring the T.E. to a point and start/finish there you can trace it with one spline after making shape.

Matthew


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Just a hobby user.
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* May 23, 2017, 08:02:50 PM
#9
Join polyline is what I was doing. I would draw the top spline, the bottom spline, and then lines on each end. To make them a single object I used join polyline. I looked for a "group selection" but could not find one. Is there another way to join the four objects into one?
It now lofts OK but it loses the curves, they become line segments so the curves are point to point line sements. Is there a setting somewhere to maintain the curves?

What I'm trying to do is only trace the tip and root ribs, loft between them, then slice at various points to get all the rib profiles in between.

Thanks

Joel

If you Group the objects you won't be able to use them as lofting profiles. If you have a TCad Pro version, there's no need to join them; just enable "Use compound profile" before lofting. If you're using deluxe, you could make each profile a single closed Spline (instead of two Splines and two Lines) and 3D-Slice the finished loft -- as I suggested in my first reply.

Henry H

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