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Tangency length for lofted surfaces

Question asked by Christine Longwell on Jun 2, 2009
Latest reply on Jun 4, 2009 by Neil Larsen

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So I'm finally trying to learn surfacing for a project I have around the corner, and it's not that hard with the exception of "tangency lengths" for start/ end conditions. Are these in units of something?

I'm sure it's obvious... Can someone enlighten me?

Christine Longwell Jun 3, 2009 6:39 PM

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Thanks Anna, I would Love to read Matt's book soon. I am watching the pennies until the new machine (and the work) comes in. The irony is that by then I won't have the time to read it

Thanks all, I think that really answers the question. I'm super impressed with the knowledge on this board!

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Kevin Quigley Jun 3, 2009 7:35 AM
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Think of these as the influence the tanegncy has at the start and end. The higher the value, the greater the influence, so a higher value will give the new surface more of a match to the existing surface, whereas a lower one yuou will see the new surface change to suit the other side faster. Best way is to try it!
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Robert Stupplebeen Jun 3, 2009 11:57 AM
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There is no unit associated with them. Spline handles also do not have units. To make it confusing it appears both of these unit-less influences use different scales. i.e. loft between 2 parallel plates with tangency and make a 2D spline with the same tangency and the same end conditions. The spline will not coincide with the loft. I hope this helps.

Rob Stupplebeen
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Robert Stupplebeen Jun 3, 2009 12:13 PM
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I just made the model to make sure.
A fully relaxed spline does match up with a loft with tangency 1. I however do not like the idea of an dimensioned spline handle for my work though. I hope this helps.

Rob Stupplebeen
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Charles Culp Jun 3, 2009 12:23 PM
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Maybe this will help you out?

http://en.wikipedia.org/wiki/NURBS

http://en.wikipedia.org/wiki/B%C3%A9zier_curve

http://en.wikipedia.org/wiki/Spline_(mathematics)
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Christine Longwell Jun 3, 2009 12:53 PM
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Thanks Charles, that was really helpful. My understanding (in the simplest, probably inaccurate terms) is that it is the derivative of the polynomial function that makes up the first section of the spline.

Now if I could just understand how to control the number of sections (it's greyed out) and the spacing of the sections, I might feel comfortable with the tool.
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Charles Culp Jun 3, 2009 1:29 PM
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You're going to have to go into more detail. What do you mean "control the number of sections" and spacing? Can you provide a screenshot (save a .png and attach it)?
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- Christine Longwell @ Charles Culp on Jun 3, 2009 3:01 PM
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  Here is an example from the SolidWorks tutorial. (Attaching really IS slow.)
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Charles Culp Jun 3, 2009 3:25 PM
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The "number of sections" that you see (in yellow) are not actually sections. They are just visual lines to help you see how the surface flows. You cannot control them in the loft tool, but if you use the boundary surface tool you can control them with the information under "Display" and changing the "mes preview" data. But again, this is just a mesh preview, and they do not control the shape.

If you want to actually have more control to the surface as it goes from one to the other you need to create a spline for the surface to follow. You can use the same curvature constraints on a spline, and then add points in the middle (the fewer the better). Then you can move the spline points, as well as control their handles, to get the desired shape you want.

The SW tutorials are great, except for surfacing. You might try Mark Biasotti's presentation at SWW2009. http://www.solidworks.com/page...ngs/presentations.html (it looks like the video isn't available yet, but you can download the .ppt). You can see his presentation from 2008, which was very similar, here: http://solidmentor.com/modules...rticle.php?storyid=323
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- Anna Wood @ Charles Culp on Jun 3, 2009 3:28 PM
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  Matt Lombard's book on Surfacing is also a great resource.
  
  http://www.dezignstuff.com/blog/
  
  See the bottom of the sidebar for the link.
  
  Cheers,
  
  Anna
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Kevin De Smet Jun 3, 2009 6:13 PM
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You can do this with surfaces or solids (SW2009), and there are really two choices.

Loft and Boundary.
Despite them sharing no resemblance in name, they actually fulfill very similar roles.
Boundary is like a Loft on steroids, more options and just generally an improved loft.

There's a good video Mark Biasotti did about boundary and other surfacing features:
http://www.viddler.com/explore/behnt/videos/24/

It's a little tricky to get the hang of it, but that video should clear up a lot. I first really found out about Boundary through that video a few months ago so I'm kind of a newbie as well you could say - what really helps is that I had to use it extensively for a part model of a mould. That project you have around the corner will absolutely definitely undeniably (should I go on?) help, you'll pick it up much faster than just casually fiddling with options in the feature(s).

Boundary (and loft as well) just give tremendous previewing, other software you just pick your curves and only at the very end it would show a preview - they're not all like that but most are. SolidWorks gives you a great idea how your boundary is evolving as you add additional curves and guides.

Hope this helps!
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Christine Longwell Jun 3, 2009 6:39 PM
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Thanks Anna, I would Love to read Matt's book soon. I am watching the pennies until the new machine (and the work) comes in. The irony is that by then I won't have the time to read it

Thanks all, I think that really answers the question. I'm super impressed with the knowledge on this board!
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- Neil Larsen @ Christine Longwell on Jun 4, 2009 3:28 AM
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  hey I think I spotted a forum babe
  I am too shy to award points though...
  
  and I see Ozzy Osborne in the same thread...cool stuff man...definitely gonna keep reading here
  
  participation is really going to surge with talent like this
  
  makes you want to do something impulsive like fill out several user surveys or somethin'...
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Tangency length for lofted surfaces

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