Trouble with Loft and two spline rails

[Anonymous]

Hi,

I am having trouble creating an airfoil shape. I have been trying to loft between profiles and use rails to control the shape. However I keep on getting the error that the rails are not attached to the profile.

The workflow I have done is:

Import the airfoil section that I want

Placed a copy on offset planes at the intervals I want

Created rails to go between each one by drawing a line close by, then setting the ends of the line as coincident to points on each of the profiles.

However each time I get the error about the rails not attached. I have done multiple different attempts but still can't get it to work. Sometimes I get one rail to work, but have never got both working. Are there any tips for making sure the rails are touching, beyond using the coincident constraint?

Link to my model

http://a360.co/2wcwlg8

I apreciate any assistants

[laughingcreek]

your loft rails actually don't all intersect.  One of those cases where the error message happens to be informative (as opposed to the vague "compute failed" message)

[laughingcreek · Accepted solution]

For your work flow, you could use the "project 3d geometry" in a sketch.  just project the pints on the foil you want to place your rails on.  turn all your profiles off, so your sketch is just showing these projected points, and then carefully draw your spline rails, making sure each one is coincident to a point.

And I'm going to add this just so it gets said.  lofting from imported curves is inviting trouble!  Yes I know, these are precisely designed foil curves that must be adhered to.  But the fact of the mater is that fusion converts all beautify made, wondrously amazing imported curves into complete garbage.  It is always suggested to rebuild any geometry to be used for lofting with native fusion curves.  You'll get away with using the imported curves some times, but when it goes bad you'll have no idea why, and spend hours hunting down the problem.

[Anonymous]

Thanks,

The projected 3d geometory worked, and the loft has completed.

It worked this time, but I can certainly see that there is no need for all of the points from the imported geometory. What would you recommend as a good way to convert into native fusion curves?

The preceision does not need to be not perfect as it will go to pot once CNC milled, then smoothed and coated anyway.

[laughingcreek]

One work flow I use with splines is to place a control point at apexes (mins and maximums, peaks and valleys, however you want to put it).  Then I make the tangent handles horizontal/vertical.  After that adjusting the length of tangent handles will usually get you there.

here's a screen cast.  The first part with the construction line skeleton isn't necessary, but can add some control.  Also, with all the little lines, the control points and tangent handles will constantly want to constrain them selves to something.  auto constraint is turned off while holding done the CTRL key (cmd for mac)

I use the above when trying to match geometry.  If I think I might want to move things around in order to play with a shape, I leave the tangent handles alone, and put more control points.  That would be more for free form.

at the end of the screen cast I also demonstrated using a sweep instead of a loft. (sweep is just a type loft with simplified inputs and functionality)  If the geometry allows, sweep can sometimes be used effectively. works here b/c the profiles don't really change.

And sweep can be more forgiving.  note that this was done with your original curves, so that rail is still not touching the profile, and yet it works.

[Anonymous]

Thanks very much for the example, it was full of ideas that I can use for different projects. I was supprised how quickly you could match the shape of the foil with such a small number of splines. The tip about using CTL to inhibit the auto snap is one I think I will use a lot.