# How do I get rid of unwanted corners inside a bent tube?

I am trying to make a clear tube in Blender and have a water simulation run through it. I made the tube out of a Bezier curve and a circle, then extruded the original until I had the shape and length I wanted. However, when I tried to make the tube thicker I had trouble with odd geometries/material showing up inside the tube at the corners, even in the finished render. Anyone have any tips on how to get rid of them? Please keep in mind I am a bit new to Blender.

I think this is a great question, because it applies to real-life engineering too. Before getting rid of that troubled geometry it helps to understand why it happens in the first place.

### Problem

The reason for the overlapping geometry is that the radius of those bends is smaller than the radius of the tube minus the thickness.

### Resolution

Either make the bends bigger or the radius of the tube smaller. If you want a tight corner tweak them so that the bend radius is about the same as the tube radius (plus or minus the tube thickness). Then use the solidify modifier in the offset direction which allows you to give it thickness (either offset towards the inside, or outside)

Whether you use bezier or spun geometry, is really down to personal taste. The bezier approach allows you to quickly edit your path, and while it will not give perfect arc bends mathematically, that might not matter for your purposes. If you are to simulate real tubing, that too is almost never perfect arc.

If you need to make a lot of tubing here's a blend that uses the sverchok parametric addon, it lets you adjust the tube radius and bend radius on the fly till you get it right.

• It might be a little involved for a one off, but if you have to do this a lot, there's nothing more satisfying than drawing the basic geometry and letting sverchok take care of the fillet / curve :) – zeffii May 8 '15 at 18:29
• Wow! Why I haven't thought about doing it this way :O ? Great solution @zeffii ! – Paul Gonet May 8 '15 at 18:30

I think using the Bezier Curve is not a good idea in this case. It is not a precise method (plus you may have a very dense geometry after converting the curve to mesh). The picture below shows the tube that I've modeled using modeling tools. I'll show you how to do it.

Add a Cylinder and place the cursor as pictured below (select the vertex, then Shift+S--->Snap--->Cursor to Selected). Now select all the vertices which form the base of the cylinder. Hit E, then RMB (or Esc).

Use a Spin button located in a Mesh Tools panel and set the proper Angle value, depending on your situation.

Reduce the Steps number. Change the Center value to make the bend more smooth.

Contnue the same process until you reach the desired tube's shape.

Remove doubles (hit W--->Remove doubles) and add the Subsurf and Solidify modifiers. Now you have the clean topology for the fluid simulation.

• +1 for the detailed instructions. Of course, if the OP wants to have the center of rotation inside the tube, as with their original Bezier curve, I assume (but haven't checked) that there will still be similar issues with this method too. – Ilmari Karonen May 8 '15 at 17:50