Holes in a tube

Rhino Rhino for Windows
1

Trying to cut holes in a tube,

Circle extruded perpendicular to wall of tube, extruded sufficiently long to perforate the tube. Arrayed (3@120)
Boolean differenced they leave three rods protruding from the tube rather than holes.

2

you’ve probably tried to boolean an open (poly)surface

3

AND the rods are now an integral part of the tube.

Tube = .625"x.500", holes/rods .125"

4

To make it simpler, start by Capping your tube so it’s closed. Capping the tube will get the surface normals pointing in the right direction for predictable Booleans.

Then when you use a Boolean Difference to subtract the rods, it should work like you expect.

Any luck?

5

You got me!
‘Cap’ fixed the problem. Not the first time, but I caught it in the past.

Thanks!

6

The Rhino tube command has a solid yes/no option. If solid=yes then the tube is created with caps so you don’t need to cap separately.

You need to have created a tube with solid=no or trimmed off the entirety of both caps for the Boolean to fail to deliver what you intended. In fact, if you have any connection between the inner and outer walls, not just caps, then the Boolean will work as you wish.

If you examine the three protruding rods, you should find there are actually six artefacts - three items that protrude outwards from the inner surface and three that protrude inwards from the outer surface. As they overlap, they create the illusion of three rods.

Rhino is looking at each surface and “tunnelling” into it from its outside (“outside” as defined by the surface normal). Rhino keeps “drilling” until it either penetrates a face that is part of the same object, whereupon it creates a tunnel wall between the faces, or it reaches the extent of the subtractor object, whereupon it creates a “well” - with a side wall and a bottom.

In your example, for the outer cylindrical surface, the subtractor rod does not extend to the far face so you get the well walls and bottom. For the inner surface Rhino is drilling outward and, with nothing to stop it, drills until it reaches the outer end of the rod, creating another set of well walls and bases.

It is doing exactly what is predictable if it fails to take account of the special case of objects with zero thickness, where it should really just make a hole. But then it is described as a solid Boolean, excluding the special case from its scope, so I guess we can’t really complain.

Regards
Jeremy