Loft "Rails" Question

[Art5]

I'm trying to use loft to bridge a gap between surfaces, when I add the guide rail it errors out on me. I read @jeff_strater 's post about lofting, and didn't find anything obvious that I'm doing wrong. It seems like if I select just one line it will work, but once I start adding other necessary lines to the chain, it error's out on me. Can anyone explain to me how this is supposed to work?

As always, any and all help is greatly appreciated.

Thanks,

             Art

 

[jeff_strater]

Hi @Art5 - can you share the design here?  According to the error message, your guide rail curve is not tangent continuous along its length.  The fix could be as simple as adding a tangent constraint, but it would be good to see the design itself.

I don't think the errors in your timeline are affecting this particular new loft, but you might want to try to get rid of them just in the interest of general cleanliness

[TheCADWhisperer]

Is there a logical reason that you have not resolved the errors in your timeline?

[Art5]

Sure thing, I've attached the file for you.

[Art5]

Logical? Perhaps not. I do have reasons though; a) When I right click on them it doesn't give me any options to help resolve them b) When I right click on them and click on 'review warning', nothing happens. Doesn't open a pop up or anything. I'm not really certain what is causing them or why, so I'm not sure how to resolve them. 

They are all extend commands.

I guess in the future I need to remember to remove my timeline BEFORE taking screenshots. 😉

[TrippyLighting]

---

@Art5 wrote:

I guess in the future I need to remember to remove my timeline BEFORE taking screenshots. 😉

---

No, in the future you should find the root cause for the problem right when you get the first warning and not plow along and ignore them. That is asking for trouble!

If you cannot identify the root cause then share that design with that error (red icons are errors!) and ask for help.

[Art5]

It's particularly tough to share the design with the errors. We are a prototype shop, all the designs are proprietary. Non-disclosure and all that fun stuff. I may be able to mock something up and post it.

[TheCADWhisperer · Accepted solution]

Because the rail is not tangent continuous, I think you are going to have to create a 3D sketch defining a closed boundary and use Patch instead of Loft.

[jeff_strater · Accepted solution]

Thanks for the design, @Art5 - I'm going to avoid the discussion over the design errors, because they don't really impact the immediate problem you are running into.  I think @TheCADWhisperer and @TrippyLighting are just pointing out helpful good practices.  And, there are cases where these such errors will cause problems, but in this case, it is not related (I think - watch Peter prove me wrong...).

Anyway, in this case the error message is accurate.  The edges you have picked for the rail curve for this loft are not tangent along their length.  If you select those edges and turn on a curvature comb map, you can see the tangent discontinuities along this edge chain:

I don't see an easy way to get around this without modifying the model, and I don't know what flexibility you have in that area.  The short answer is that a rail curve must be tangent continuous for loft.  You might be able to fill in this area with a Boundary Patch, if you sketched a curve across the open edge, but I'm not sure that this is what you want to do.

[Art5]

I really appreciate your input, I have a question though. The file you've attached looks different than the screenshot in your post. In your screenshot the 'bottom' connecting line that you've created appears to be a straight line, however in the attached file it's got a nice curve to it. 

The attached file is certainly a viable solution for what I needed to do, I'm just curious how you achieved it.

[TheCADWhisperer · Accepted solution]

I didn't like the straight line, so I replaced it with a tangent spline.  You can edit the curvature of the spline as needed (perhaps to reduce the bulge).

I started a new sketch.

Project>Include Edge

selected the beginning and ending edge curves.

Created Spline and added Tangency constraints to the projected edges.

[Art5]

Thank you for explaining this to me, I thought that the edges just had to be coincident to be continuous. 

I did start a separate thread to try to address the error issues.

I'm afraid I cannot modify the 'part' data, as that would change the form of the part, but I do have a fair amount of freedom to do whatever I need to do outside of part. I pretty much always build from the part data sent to me by the customer, retain the original data, and seldom modify it unless it can't be built. The extends are all outside of part, extended from the edges of the original part data. The non-tangent continuous edges are the edge of the original data.

The patch that TheCADWhisperer provided would work, really the only thing that I have to avoid is putting corners in the runoff that would cause creases or buckles in the part when I go to stamp it.

[Art5]

Alright, I can use the patch you provided to move forward with my part, but I went ahead and re-created it on my own so that in the future I know how to do it. 

I'm still going to use the patch you sent over for the actual die, since you took the time to make it.

I'm going to go ahead and accept both jeff.strater's answer and yours as solutions to this thread, thanks a million!

[TheCADWhisperer]

---

@Art5 wrote:

.... thanks a million!

---

Please make that payable in $USD$  🤗  Hawaii here I come...