Subtracting a surface from a solid

I am trying to do something that I should be able to but am having trouble. I want to make a long box .625 inches square and 12 inches long. On each side there will be a groove 4 inches long. Here’s what I’ve done so far.knife-rack-twist.3dm (91.5 KB)
It is a box and I have made 4 surfaces in the shape of the groove. Now I want to subtract those grooves which are not solid, only surfaces from the surfaces of the box. I’ve tried various things like boolean difference but don’t get what I expect to get. The box usually disappears completely, or I get something where when I look at it in pen mode I see the rectangular outline of the groove but not its interior. There is probably a better way to do this so feel free to tell me I’ve started wrong and how I should have done it.

knife-rack-twist-EDITED.3dm (201.4 KB)
Is this what you want to do?

Hello - if Booelan operations return unexpected results (as distinct from none…) then some or all of the objects are open. Use the Dir command to flip the surface normals to point to what you consider to the the outside of the objects and that should sort it out.


Not exactly. I don’t want the groove surfaces floating. I got something to work in a hacked sort of way. Here’s the result with the bar twisted.knife-rack-twist.3dm (1.1 MB)

Thanks, I’ll look into that. I had to create false surfaces and subtract those from the box then join the grooves I had made to the result. I continue to have trouble understanding some terminology in Rhino after a year’s useage. I understand the Dir command but not the implications and I’m unclear by what you mean when you say objects are open.

An open object is not a solid object. An open object has naked edges.

Hi Joe - if objects are open (e.g. a box with one side missing) , as opposed to fully closed solids, then Rhino may not agree with you as to what is the outside of the object - it cannot tell - so the Boolean may be the reverse of what you expect. With fully closed objects there is no ambiguity…


thanks, David and Pascal. Makes sense.