how to close these holes?

 From:  Michael Gibson
5480.7 In reply to 5480.1 
Hi wim, so yeah like bemfarmer mentions above the circular hole can just be deleted by an "untrim" operation (select the open edge and hit delete). Some more information on untrim here:

For the second kind of hole, the easiest method for that is to make your base object into a solid and then use a 2D side profile curve to cut away the material in the first place. Doing it that way will produce "side walls" automatically and you won't have any hole to fill in at all.

See these posts for some examples and explanations:

It looks like you may be doing something like using Edit > Trim to cut the surface up by a side profile then leaving that hole - dont' do that, instead make sure your base object is a solid and then use boolean difference to cut it rather than Trim, the booleans are more oriented towards keeping things as solids while trim is a surface modeling operation. Behind the scenes the booleans will do the equivalent of an extrude of your profile curve, trim both the base solid and the extrusion, and automatically keep and join the right pieces to make new solids with "side walls" on them. So it can save a lot of time to use the booleans since it bundles up a fair amount of other low level operations in it, you'll be doing a lot more work if you try to do all those low level operations each individually.

If you did want to do things in the "low level" way to fill that kind of hole you have there you would not want to be working only with the 3D edge curve that's the result of a trim but instead extrude out the original 2D cutting profile so that you have the extruded surface and then also trim that extruded surface to produce the side wall cap part, one of the links above shows that method. But it's far easier to just use a boolean instead and then have no holes at all to deal with filling...

- Michael