# How to model a cylindrical extrusion that looks similar to an octagonal prism?

How do I model this cylindrical extrusion with circular base?

I first tried starting from a cylinder, although, when it comes to give thickness (by converting it to Curve/Geometry/Depth) the structure deforms and appears uneven.

I made a second endeavor by starting from a duplicated Circle, and extruding the circular vertices to match them with the other sides and finally applying a Solidify modifier but I got the following results, which are far from the object:

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Your desired mesh can easily be modeled using T-Joints. Luckily you don't have to model these because they are readily available within the built-in addon Add Mesh: Extra Objects. Enable it under menu Edit > Preferences > Add-ons and search for "Extra Objects".

Press Shift+C to ensure the 3D Cursor is at the World Origin, and add one T-Joint object via menu Add > Mesh > Pipe Joints > Pipe T-Joint. Customize the properties of your object such as the radius within the Adjust Last Operation popup that appears in the lower left corner. Rotate the joint on the Y-Axis by 90 degrees and press Ctrl+A > Apply Rotation. Then add a Circle curve via menu Add > Curve > Circle.

Select the pipe and add an Array Modifier and set the Count to 8.

Then add a Curve Modifier and set the curve you added as the Curve Object.

Now to distribute the 8 joints in an even manner, press Numpad 7 to go into top view, and adjust the circles scale and/or the Array Modifier's Factor X (or Factor Y depending on the orientation of your object) property value.

Select the pipe objects and press tab to enter Edit Mode. Alt+LMB click one end of the pipe object to Select Edge Loop and press E to extrude and press X to extrude it along the X-Axis. Make sure the extruded edge aligns perfectly to where the end of the neighboring pipe's edge used to be aligned at. Then set the Factor X back to 1.0 so they stick side to side. You may need to frequently jump back and forth into Object/Edit Mode to view the result if the ends perfectly align on the curve. Also make sure the Array Modifier's Merge property is ticked.

Add some Loop Cuts to the extended region to add more geometry so it can bend more smoothly.

Once you're happy with the output you can convert the entire object to a single mesh by either applying all the modifiers or right clicking the object and selecting Convert To > Mesh. Select all the Edge Loops of the upper pipe opening and extrude it along the Z-Axis with EZ then press Shift+S > Cursor to Selected to bring up the 3D Cursor. Now tab back into Object Mode and right click the pipes and select Set Origin > Origin To 3D Cursor.

The previous 2 steps are needed for the Mirror Modifier you will add now, and mirror it along the Z-Axis. Convert to mesh and tab into Edit Mode and press AM > Merge By Distance and increase the Merge Distance to maybe 0.001 or 0.005 to make sure all vertices have been merged. Then you can optionally add a Subdivision Surface Modifier to make it nice smooth with levels 2 or 3.