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Loft problem

geoff_joseygeoff_josey Member Posts: 62 ✭✭
After early posts and help with lofting I have made some progress - albeit slowly.
I am now trying to understand the cause of the strange loft between 2 aerofoil sections.
I have spent some time playing around with the settings without success. I think the outlines are not duplicated as per previous problem.
See Rudder061220



  • PrachiPrachi Member, OS Professional Posts: 262 ✭✭✭
    edited December 2020
    Your NACA 10 air foil sketch wants to be a closed area. Some thing is not connected. Notice how the other profile shows a shaded area inside that indicates it is closed. I didn't check your profiles but lofting works easiest when the number of segments is the same on both profiles.
  • geoff_joseygeoff_josey Member Posts: 62 ✭✭
    Hi Glen, Thanks for your comment. Very helpful. I went carefully round the NACA 10 profile, but could not find anything that did not look closed. I then lofted again again it works !!
    When select loft and then the 2 outlines via the features menu it works fine. When I try it selecting from each sketch it takes a long while and then comes up with an error. Not sure why. 
  • romeograhamromeograham Member Posts: 636 PRO
    Some folks have posted issues lofting airfoil profiles before.
    One issue that I found was that the imported airfoil profiles actually had multiple lines on top of each other in many areas but not all the lines were duplicated. This meant that for some users, it was very difficult to make the correct selection - sometimes they'd select the entire profile (accidentally) by selecting the face, and other times (trying to select the edges of the sketch) they's select part of the open profile.

    I can't tell if that's an issue with this specific post, but for general "lofting airfoil profiles" issues this has come up more than once on the forum.

  • bruce_williamsbruce_williams Member, Developers Posts: 842 PRO
    good points on duplicate lines.

    What tricks/methods help find duplicates? 
  • romeograhamromeograham Member Posts: 636 PRO
    I think I found it by trying to figure out why the selections didn't work as expected in those sketches...and then some trial and error select, delete etc.
    Using box-select (using both "to the right" and "to the left" selection), as well as Create selection > Edges > Loop / chain connected also helped to investigate.
    Once you're aware there may be duplicate lines, it's not too hard to find them...it's when you don't know they're there that things are super-hard to figure out. The sketch & selections just don't behave right. For new Onshape users particularly, this is a really difficult thing to troubleshoot.

    It's interesting, the waves of problem types that come through the forum. Often they're related to excercise sets used in education (remember the many boolean problem posts of that multi-cube puzzle part people were trying to make, back in the darkest days of 2020?), and feature very similar problems - either with the excercise, the instructions, or the challenges of learning a new CAD system remotely.
  • bruce_williamsbruce_williams Member, Developers Posts: 842 PRO

    Please see the post thread below describing using dividing lines to find open geometry. This is a little late to your OP but may help diagnose issues in future.  I am sorry, I do not remember who first posted this method that some call 'binary search'.  It is surprisingly efficient.


  • bruce_williamsbruce_williams Member, Developers Posts: 842 PRO
    good tips on finding duplicates. I think 'select other' helps discover and deal with them too.  You are right - these are the esoteric kinds of issues that can stymie newer users (and older ones speaking from recent experience). 

    It is good to know how to find problems and then it is OK to delete overly complex or duplicate geometry. Especially working with imports.

    I have noticed the 'waves' of common parts/issues too!  It has been fun to see the holiday theme surging lately.  Glad we have new people discovering this pretty awesome package.
  • PrachiPrachi Member, OS Professional Posts: 262 ✭✭✭
    edited December 2020
    Good reminder on dividing lines Bruce. 2 openings on the NACA 10 sketch.

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