How to repair a 3ds max Boolean

Written by Conny Klasson, februari, 2003, any comments are welcome.

This looks fairly easy, we want to "boolean out" two cylinders out of a box.

In this example the box is made with this settings:
Length: 5, Length Segs: 1
Width: 3, Width Segs: 1
Height: 4, Height Segs: 1

And the cylinders:
Radius: 1
Height: 4, Height Segs: 5
Sides: 18, Caps Segs: 1
This is what we want, a clean mesh as the result of the boolean operation.

 
This is what we get.
To see the mesh in detail:
1. Apply "Edit Mesh" modifier
2. Go to Edge sublevel.
3. Select all edges.
4. Scroll down to Surface Properties rollout, click the "Visible" button.
5. Set the View Port to show "Edged Faces".
A mess of unwanded faces, zoom in to see in detail:
Qestion: What happend? Answer: "To much difference in objects mesh density".

1. If we want to cut out a quarter or a half of a cylinder, make sure the number of Sides are multiples of 4. The default value is 18, change to16 or 20, in this case it was changed to 16.

2. The height segments, a box default value is 1 height segment. The cylinder's default value
is 5. Change the cylinder's height segments to 1.
Much better now.

It's a bit tricky to change the properties of the boolean's operands.
1. Select the boolean object.
2. Go to Modify tab.
3. Select one of the operands in the list. Selected operand should now show at the bottom of the stack.
4. Select the operand object and change the parameters.

If you have trouble with this, simply start from scratch with new objects.
Still some wierd things going on at the top of the mesh. Again, this is due to too much density difference.
Lets go back to when the first cylinder was "booleaned out":

Some long thin faces are created in the box to match the cylinders segmentation.
Add some segments to the box,
3 length segments and 2 width segments.
And this is wih the other cylinder taken out. Not perfect yet, but at least there are no long thin faces.
Still some troubles, use the "Weld Target" feature at vertex sublevel
in Edit Mesh to get rid of the last unwanted faces.
Drag unwanted vertex and drop on wanted vertex.

Do not use "Weld Selected" this can disort the geometry because
you don't have control over where the final vertex is placed. On a more organic model, weld selected works well and much faster than the manual weld target feature.
To even more reduce the long-thin-
face-syndrome, use the "Turn" feature in Edge sublevel.
Click the "Turn" button then select the edge that you want to turn. The goal is to make the edges as equal in length as possible.
Tip: Check "Ignore Backface" to prevent edges at the backside of the model to be turned by misstake.

Dont forget to fix the bottom side of the model.
Finally make the "internal" edges invisible.
1. Go to Edge sublevel.
2. Scroll down to "Surface Properties"
3. Select edges to hide.
4. Click the Invisible button. (How do you click an invisible button?)

To make sure the mesh is valid after the boolean operation apply the "STL Check" modifier.
It should not report any errors.