THE QUIRKS OF LOFTING
One of the first modeling techniques that most MAX users learn is lofting. Almost all of us know the basics -- a path, a shape to loft, then you click a few options and there it is. But sometimes the object doesn't turn out the way you expect it to. This tutorial explores some of the quirks of lofting.

The pictures below show a circle lofted along a straight path with just two vertices, one at each end. It can come out looking very different even though it seems like you're doing the same thing. If you've ever tried to loft a shape and ended up with any of the following, then you need this tutorial!
Has this ever happened to you?
You start with a path and circle, and you expect the loft to look like the picture at right. You might instead end up with unevenly spaced segments,
a slanted cap at the end,
a sharp, indented or rounded nub,
or a long spike sticking out.
When any of these strange-looking problems occur, it is because a vertex at the end of the path is set to the wrong type. A vertex at the end of a loft path should never be a Bezier or Bezier Corner type, but should always be a Corner or Smooth type.

In this tutorial, we'll recreate all these lofts, including the one that looks right, so you can see how the vertex type on path end vertices affect the look of the loft.
How to do it right

  1. In the Top viewport, create a line. Give the line two vertices, one at each end. Click at the left side of the viewport to start the line. Move the cursor to about 3/4 of the width of the viewport. To set this vertex, click and drag to the right until the cursor reaches the right side of the viewport.



  2. Release the mouse, then right-click to end the line.



  3. Create a small circle to loft along the line.

  4. In the Top viewport, make five copies of the line. Spread the copies out so you can see them easily. Be sure to leave enough space between the lines so you'll be able to see the lofts when you make them later.



  5. Select the first line. Go to the Modify panel. Expand the Line listing and highlight the Vertex sub-object level to access it.

  6. Select the line's rightmost vertex. Right-click on the vertex. The Quad menu appears.

    The four possible vertex types appear at the left side of the menu, with a checkmark next to the one that is currently chosen.

    Smooth - Forces the segments into a smooth curve.
    Corner - Makes the segments straight as they leave the vertex.
    Bezier - Provides a tangent line and small green handles that can be moved to change the shape of the curve around the vertex. The handles always move together to keep the line straight and tangent.
    Bezier Corner - Provides handles which can be moved independently to make a sharp corner, smooth curve or any shape.

    The current vertex type should be Bezier. If it is not, you will need to start over from step 1. Otherwise, you won't be able to simulate the bad effects in later steps.

  7. On the Quad menu, choose the Corner type.

  8. Turn off the Vertex sub-object level by clicking on the main Line level.

  9. Select the second line. Access the Vertex sub-object level and select the line's rightmost vertex. The Bezier handles appear around the vertex. Leave this line as is. Return to the Line level of the object.

    On the remaining lines, you will need to access the Vertex sub-object level to work with the vertices, then return to the Line level before you can select the next line.

  10. Select the third line and select the line's rightmost vertex. The Bezier handles appear. Zoom in to the vertex and handles. Click on Select and Move and turn on Restrict to X. On the left handle, click and drag to the right until the handle is almost on top of the vertex.



  11. Select the fourth line. Select the line's rightmost vertex. Pick up the left handle and move it close to the vertex. Move the handle up a little so the line between the handles goes at a slant.

    The handles must be quite close to the vertex in order to make them slant while still keeping the line straight. You might have to zoom in pretty close to get this effect.



  12. Select the fifth line. Pick up the left handle and move it up and over to the other side of the vertex until the line between the handles goes straight across horizontally. The original line that you drew should go straight across after you've placed the vertex.

  13. Copy the fifth line to make a sixth line below the fifth line.br>
    Now you're ready to loft.

  14. Select the first line. Go to the Create panel and make sure the Geometry button is clicked. Select Compound Objects from the pulldown list, and click Loft. Click the Get Shape button and click on the circle.

    Expand the Skin Parameters rollout and check the Skin checkbox.

    You should be able to see the lofted object in all viewports, and it should look fine.

  15. Select the second line, and loft the circle on it in the same manner. Repeat for each line until you have six lofts.

    Now take a look at the lofts. You should observe the following:
    Second and third lofts - Segments are unevenly distributed
    Fourth loft - One end has a slant
    Fifth loft - One end looks as if is has been pinched and folded over

    The sixth loft looks just like the fifth loft. To observe some different effects, select the sixth loft object (not the line, but the loft object itself) and go to the Modify panel. Under the Skin Parameters rollout, change the Path Steps to different values such as 10, 20, 30, 40, 60 and 100. Observe the loft object as you make each change. With some Path Step values, the end of the loft juts out in a big spike.

    Next, we'll fix these lousy lofts.

  16. Select all the loft objects, but not the lines. Go to the Display panel and click Hide Selected to hide them.

  17. Select the second line. Go to the Modify panel. Go to the Vertex sub-object level and select the rightmost vertex. Right-click on the vertex and change its type to either Corner or Smooth. Return to the Line level.

  18. Repeat this process for each line.

  19. Go to the Display panel and click Unhide All.

    The lofts appear, and they are all fixed now. Note that you changed the loft simply by changing the existing line being used for the loft.

    From this tutorial, you should be able to see that Bezier vertices make lousy end vertices for a loft object, while Corner and Smooth work just fine on the ends. Bezier vertices work great as middle vertices, though.

    The next time you do a loft, check the ends of the loft path to make sure the end vertices are either Corner or Smooth types, and all will be well.