Align cross-sections perpendicular with path ends (LOFT command)

[nick.ollila]

I need to use the LOFT command on this particular spline and need to align the circles (cross-sections) so that they are perpendicular with the spline (path). I know if I was using the SWEEP command it would automatically place the objects perpendicular to the ends. But I can't use the SWEEP command in this particular instance because I'm starting and finishing with 2 different diameters.

Does AutoCAD for Mac 2016 have a quick way of doing this? What would be the most precise way of doing this? 

I've attached the drawing for reference.

Regards,

Nick

[maxim_k · Accepted solution]

Hi Nick,

You can make SWEEP command work for you:
Create a copy of spline and first circle, than use SWEEP command to sweep the circle along the spline with base point at the center of the circle. During sweep operation the circle will be aligned perpendicular to the path.

Now explode the resulting 3D Solid - you will get Region object at the end point of the spline which is aligned correctly. Now move this region to the end point of the spline which you want to use as a path in the LOFT command.

Repeat the same for the circle at the other end of spline.

Now use LOFT command and pick Regions as cross sections, than use spline as a path.

Maxim

[ntombling]

One of the things I like about AutoCAD is there are many ways to do the same thing. I'm not a 3d expert, but thought i'd give it go. I got a messy solution, and there is likely a much tidier way. I wouldn't mind knowing a better way too.

What I did was copied your spline twice (so a total of 3 splines on top of each other). I used sweep twice to align the circles and create two pipes of different diameters at each end. Exploding both pipes leaves you with 'regions' at both ends of the spline aligned correctly. I then used loft on two different sized regions, which creates a loft on a straight line path (and looks weird). Working through the loft command you can then select the spline as the path to follow.

The other way I was looking at was in relation to the control vertices of spline, then using maths to work out which direction the circles should be drawn. It's a pity you can't snap to the control vertices could that could work too I think.

Edit: Beaten!

That's awesome Maxim - I thought there'd be an easier way though!

[maxim_k]

The second way with control vertices of spline will work too.
At first you need to switch spline from showing Fit to "Control vertices".
Now draw line from the end point of spline in any direction. Now select both line and spline, select "free" end of the line (the grip turns in red) and stretch this endpoint (turn off ortho) to the blue circle grip of the spline.
When you are very near to this spline control vertex, you should notice that the ent point of line you are stretching "snaps" to the control point of the spline - release mouse - now you have line tangent to the spline direction at the end point of the spline.
Next step is to draw auxilary line from the center of the circle which should go in Z direction. Now use ALIGN command to align the circle using end points of this auxilary line and the line you have in tangent direction to the spline's endpoint.

Maxim

[ntombling]

Well there you go, another way to do it. Two ways I've never used AutoCAD before!

[nick.ollila]

Hi Maxim,

Thank you for your quick response. I know I can always count on you for a solution.

Your solution works well with cross-sections placed at the ends of the path, but how do I align multiple cross-sections of varying diameters between the end points of the path? I have used the XLINE (per to) command and then placed a UCS at the intersection, rotated the UCS 90° about it's X axis, and then placed my cross-section. That seems a bit cumbersome... Perhaps you have a cleaner/efficient way of doing this.

Regards,

Nick

[nick.ollila]

Hi Maxim,

I'm unable to make this suggestion work. When I select the "free" end it doesn't stretch, it shrinks to a point when it snaps. Please send example if you have time.

Regards,

Nick

[maxim_k]

Hi Nick,

>>>When I select the "free" end it doesn't
>>>stretch, it shrinks to a point when it snaps

You don't need to use object snap in this case. Turn off all object snaps, grips will snap to each other without object snap enabled.

Maxim

[maxim_k]

---

@nick.ollila wrote:

...but how do I align multiple cross-sections of varying diameters between the end points of the path? ...

---

Hi Nick,

One of the ways, I think, could be using associative array (path array) as an aid in placing cross sections along loft path.

See attached drawing for details.

Maxim

[nick.ollila]

Hi Maxim,

It still doesn't work for me. The line snaps to a point. I select the free end of the line and drag it back to the spline end and when it snaps to the spline grip I release the mouse and the line is gone, just a point!!  Could you please send a drawing to explain how you are able to accomplish this?

[nick.ollila]

Well done Maxim!

[maxim_k]

Hi Nick,

Here how I get this to work:

Maxim

[nick.ollila]

Hi Maxim,

That line is not perpendicular to the end point of the spline. How do you make it perpendicular?

Nick

[maxim_k]

Hi Nick,

Yes, it is tangent to the endpoint of spline. If the spline is "flat", simply rotate the line 90 degrees and it will be perpendicular.

Maxim

[nick.ollila]

Hi Maxim,

Got it! Thank you for all your help.

Regards,

Nick