Part 1. The basics of creating a hole.
A 'round' hole (when smoothed), starts life as not being round at all. How 'not round' to make it though depends on the mesh you wish to put the hole into, but there are some general guidlines, or more a 'format' which you can follow and then adapt to your specific requirements.
So, the easiest way to show this is with a few images, sorry there is no video but my hardware just isn't up to the job.
Lets take a simple 9 polygon plane object, (converted to ed poly). in which we want to create our hole:
First select the poly in which you wish to create your hole:
Then select 'Tesselate' from the command panel and choose 'face'.
Then click 'Apply'......
and then choose 'Edge'....this then tesselates the poly into something resembling an 8 sided poly in the middle.....the basis for our hole.
And from the 'Top' view.......
Select the centre 4 poly's that make up the middle......and delete them.
And from the 'Perspective' view....
When 'Smoothing' is applied we can see that the 8 sided 'hole' is now round. Iterations for the smoothing here were at 2.
And a quick render gives us.....
The more observant among you will notice though that the 'hole' isn't exactly a perfect circle....compared to a circle you can see the difference.....check out the parts nearest the corners.
This odd shape is simply because of using 'Tesselate' to divide the original poly. The corners of the 'Square' poly are obviously further away from the centre of the square and so the length of the 'edges' connecting them are slightly shorter than they should be, pulling the circle slightly outward. We have several options to correct this. Moving the verts to create a 'perfect' 8 sided NGon is the easiest, but this depends on your surrounding mesh as to how easy.....you may find another method to be easier.....this is something you will have to decide for yourself.
One way to do this is to create an 8 sided 'NGon' in the middle and use it as a template to move the verts to the right place......you can see the difference more clearly here.
You can use the 'Constrain to...' when moving verts to prevent deforming the mesh, (more important with curved meshes than with flat ones but still...)
Once the verts are moved into a more even position, and with smoothed applied, you can see that the 'hole' is now more or less a perfect circle.....
And when rendered.....
Instead of using 'tesselate' and then moving verts, we could adopt a different method whereby we create the 'hole' FIRST, and then attach it to the original mesh...sound odd? It does....but this works really well and can be applied to almost any situation where you need a hole. The benefit of this is that you don't need a 'square' poly in your mesh.....something which is rare in a mesh anyway.
We start by removing ALL the poly's that cover the area where we want the 'hole'.......
Then, we create an 8 sided poly of roughly the right size of the desired 'hole'. How you do this is up to you......I just created an 8 sided NGon and converted it to an Ed Poly object....this automatically creates the polygon....instead of 'capping'.
One IMPORTANT thing to note is to keep the new object in line with the original....with 'Plane' objects such as these it's relatively easy to do but when your mesh is 'curved', as demonstrated in Part 2, it's essential to keep an eye on it....get into the practice of 'Aligning' pivot points and objects NOW.
Next, select the surrounding 'edges' and 'extrude' them using the 'scale' tool and holding down 'shift'. Make sure the new edges stay within the boundary of the poly's you removed earlier.
Once this is done delete the poly in the middle to form a 'ring' of polys. This may seem strange, but we know we need a 'LOOP' of edges to form the hole, the inner ones, but also some edges to join to the rest of the mesh...the outer ones. moving these edges/verts will not deform the inner edges/verts so keeping our 'hole' round...(well 8 sided anyway).
To 'Target Weld' those outer verts to the Mesh we need to attach these new poly's to the Mesh first......
Now that the poly's form just one object we can 'Target Weld' the OUTER verts of the ring to the original Mesh......
You may find that to weld ALL the verts you need to use 'Insert Vertex' on some of the original 'edges'......
Once the verts are welded and 'Smoothing' applied we get a similar result to before.....
And rendered.....
We can clean the mesh a little by 'Cutting' some new 'edges' from those centre verts....the ones top, bottom and both sides.....
This doesn't deform the hole nor the mesh, but when the smoothing is applied you can see that the lines of 'edges' flow more smoothly around the 'hole'.....
The advantage of this is that should we want to extrude the hole to form a 'Tube' the lines of 'edges' will still flow really well....this also helps if we need to 'Chamfer' the 'fillet' or even cut some more 'holes'....a clean flowing mesh is ESSENTIAL to keep the workload down to a minimum.
And rendered.....
Thats about it for making holes.
Part 2A will use an example to further demonstrate how to create the 'hole' FIRST...and then attach it to the mesh...but on a 'Curved' surface.
Regards.