"Simple" Beginner Loft Question -- Why is it twisted?

julian_frost

I've created a simple OnShape document.

It's a cylinder. A few millimeters above the cylinder is an offset plane. Drawn on that offset plane is a rectangle. The rectangle is extruded 25mm. What we end up with is a box floating above the cylinder.

Now… I want to make a Loft that joins the bottom of the box to the top of the cylinder. I used the Loft tool and selected the bottom of the box and the top of the cylinder, and presto, there's a loft, just as I expected!…

But… the loft is twisted. When viewed from above, this is what I get:

What I want, is a smooth, symmetrical transition from the box to the cylinder, so it doesn't look like it's twisted. Is this possible? Here's a link to my document:

https://cad.onshape.com/documents/b30c9343f8f5c1436581b627/w/c882f479e89d3a413a282633/e/8cfe950ba7d64e61d8916ccd

If it's possible, can you copy my document, make the changes and share it with me so I can see what you did?

Thanks.

julian_frost

Since I can't delete my own posts… I'll answer my own question here:

Edit the Sketch that defines the box. Add a Point to the center of the two long sides. Edit the Sketch that defines the top of cylinder and add two Points at opposite sides of the circle. Create a Loft and select the bottom of the box and the top of the cylinder. Click the Connections box. Select one of the Points on the bottom of the box and then select the Point "underneath" it on the circumference of the top of the cylinder. Click the arrow next to "Selections" to collapse the selections. Now add the other two Points. These will go into their own section. In the image below, I've added the first two points and collapsed the selection. Then I added the second two Points into their own selection:

Finally, I click the check mark and the Loft is created, without any twists!

In my real document, I created 8 points for the box - one in the middle of each side and at the corner of the box. I created corresponding Points equally spaced around the circumference of the top of the cylinder. I selected each Point, individually, from the box and the cylinder, then collapsed the Selection before selecting the next two matching Points. The result was a perfectly formed Loft from the box to the cylinder:

Hope that helps if anyone else is having the same issues.

julian_frost

Since I can't delete my own posts… I'll answer my own question here:

Edit the Sketch that defines the box. Add a Point to the center of the two long sides. Edit the Sketch that defines the top of cylinder and add two Points at opposite sides of the circle. Create a Loft and select the bottom of the box and the top of the cylinder. Click the Connections box. Select one of the Points on the bottom of the box and then select the Point "underneath" it on the circumference of the top of the cylinder. Click the arrow next to "Selections" to collapse the selections. Now add the other two Points. These will go into their own section. In the image below, I've added the first two points and collapsed the selection. Then I added the second two Points into their own selection:

Finally, I click the check mark and the Loft is created, without any twists!

In my real document, I created 8 points for the box - one in the middle of each side and at the corner of the box. I created corresponding Points equally spaced around the circumference of the top of the cylinder. I selected each Point, individually, from the box and the cylinder, then collapsed the Selection before selecting the next two matching Points. The result was a perfectly formed Loft from the box to the cylinder:

Hope that helps if anyone else is having the same issues.

glen_dewsbury

Here is another sample for thoughts.

https://cad.onshape.com/documents/e7deb849eaf79cbe21dd8d77/w/d33b9654867f8aafb9a49fde/e/7855a2cc995f407f46e58925