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Hope all of you have seen pipe flanges. They are being using every where to connect pipes together or to connect pipe bends, Ts and valves. These flanges can be categorized into several categories according to minor difference among them. However, in general terms it is flat circular dish with a large circular hall at the centre and several smaller holes near to the circumference which are used to connect the flange using nuts and bolts. Another notable thing with these smaller holes is, they are always come as a multiplication of 4 (as 4, 8, 12, 16 …).
Let’s start the lesson with this general idea. You can use the method I present in this tutorial to model both low-poly and high-poly pipe flanges.
To start the tutorial, go to Create > Geometry > Standard Primitives > Object Type rollout > Cylinder and draw a cylinder with less height when compared with the diameter. If you are going to model a real-world flange, use correct dimensions right from the brining. Set the “Radius:” of the cylinder to outside flange radius (half of the outside flange diameter) you need (I am using 125 mm) and Height to flange height (I am using 20 mm). Set “Height Segments:” and “Cap Segments:” to 2. Decide how much bolts you  are going to use to fix this flange, multiply the number by 2 and place it as the value of “Sides:”. If you are not modelling a real flange, use less number of holes for smaller flanges and use higher numbers for bigger flanges. Don’t forgot to chose a number which is a multiplication of 4 (I am using 8 holes).

Now you should having a short-flat cylinder like below.

Select the created cylinder, right click on it and converted to an Editable Poly. Go to Edge Sub-Object level, select all the edges of the circle on the top face (select one edge and the press “Loop” button under “Selection” rollout) and scale it to the size you need as the outer diameter of the pipe.

Select the edges inside the ring, add another ring inside the first ring by pressing “Connect” button under “Edit Edges” rollout and change the diameter of the new ring by changing the “Slide” value as required as the internal diameter of the pipe.


Then go to Polygon Sub-Object level of the object, select and delete the bottom half of the object from the Front viewport.

Go to top viewport, select and delete all the polygons, only keeping to triangular parts (see the picture below).

Now, go back to Perspective viewport and see. If you have done the job correctly, the object should have only 8 polygons.

Delete the 2 triangular polygons as well (now it is remaining only 6 polygons).

Select the 2 smaller polygons on the top surface, and extrude them a bit (maybe half of the flange height) using “Extrude Polygons” (use “Extrude” button under “Edit Polygons” rollout).

When “Extrude” it will generate 2 more nearly square polygons on both sides of the extruded part. Delete them.

Select the 3 long edges of the two large polygons on top and insert a new edge at the middle of them using the “Connect” option under “Edit Edges” rollout.

Turn on snap, go to Create > Shapes > Splines > “Object Type” rollout > Circle and draw a small circle on the top plane around vertex marked in the picture above. We are going to use this circle as our reference for small holes place on the flange. So you can resize it as you like. To do that, go to “Modify” tab and change the “Radius:” under “Parameters” rollout as you like. Then go to “Interpolation” rollout and reduce the number of “Steps:” to 1. Now, you should have an octagon around the vertex as you see below.

Go to Top viewport and see whether any of the two vertices of the octagon are going through the edges of the major object. If not, turn on “Angle Snap Toggle” with a snap “Angle” calculated using (360°/(number of holes x2)
(for me it is 22.5° (360°/(8×2) = 22.5°) )  and rotate the octagon (circle) to bring 2 of vertices on top of the edges.

Select the main object and make the edges of the octagon on the main object using the “Cut” tool under “Edit Geometry” rollout starting from a vertex on a line (keep Snap on). Once mark the octagon, we do not need it any more – you may delete it.

Go to Polygon Sub-object level and delete the 4 polygons inside the octagon, to make an octagon hole inside. Go to Vertex Sub-object level and weld the marked vertices of the above image to the vertices nearby using the “Target Weld” tool available under “Edit Vertices” rollout. Now you should get something like below.

Then connect the 4 unconnected vertices of the octagon to 4 major vertices of the object (see figure below) using the “Cut” tool available under “Edit Geometry” rollout.

Go to Edge Sub-object level, select the 8 vertices of the octagon and extrude them down-words to an amount equal to half of the flange height (for me it will be 10 mm) using the “Extrude” tool available under “Edit Edges” rollout.

Select all the marked edges in the following figure and double the lines by chamfer them to a small amount using “Chamfer” tool available under edges “Edit Edges” rollout. If you like to have different amounts chamfer, select the edges as groups (as numbered below) and apply “Chamfer” separately.

Once you complete the above step, you will see 4 small triangles are formed. We need to remove them. To do that, go to Vertex Sub-object level and attach inner vertices of the triangle to outer vertices using the “Target Weld” tool. Make sure to maintain the double lines. If you one everything correctly, you should received something like below.

Now we have completed modelling the basic shape we required. Don’t worry if you can’t see a flange from this object. You will see it sooner.
Take a mirror copy of the object along the Z axis.

Then, place the mirror object to touch with the edges of the mother-object as you can see below (use Snap tool). Attach the mirror object to the mother object using the “Attach” button available under “Edit Geometry”.

Go to Vertex Sub-object level and select the 6 vertices marked below.

Use one of the “Select and Scale” toggles and decrease scale along the Z-axis to 0 or near 0 until you see them touch (see figure below).

Select all the vertices, and press Weld the un-weld vertices. Make sure not to lose the double lines while you are doing that.
Then go to top viewport, select the object and “Select and Rotate” toggle available on the top. Turn on Snap (change the angle as appropriate) and rotate the object by holding the “Shift” key until it exactly passes the boundary of the first object. For me it is exactly 45°, and you may get 90°, 22.5° etc. Once you rotate the object to the correct amount, release the mouse press. Then it will appear “Clone Options” dialog asking the number of copies required. Set the number of copies as required to complete the flange (I need 7 more copies) and press OK.

Hope you got something like below as the result.

Select one of the objects and attach rest of the objects to it, as you done to correct the mirrored object. Now there is only one object, to make it complete, go back to Vertex sub-object level, select all the vertices and Weld once without losing the double lines. Exit from the sub-object level apply TurboSmooth modifier from the Modifier list with 1 or 2 Iterations. Hope you got a quality pipe-flange the result. This is what I got.

Render and see how it looks like.