Selecting the face of a small object on top of the stack

[ervandarnell]

I'm just getting started on cadquery as an upgrade to openscad. I want to create this cleanly:

It's trivial like so:

cq.Workplane("XY")
.box(2,2,2).faces(">X").workplane()
.box(1,1,1,centered=(1,1,0)).faces("<Z").workplane()
.box(5,5,1, centered=(1,1,0))

But the problem here is the box222 is first in the chain. This won't work for a bigger design. The box551 is a platform to build multiple things on, thus it really needs to be first in the chain:

.box(5,5,1, centered=(1,1,0)).faces(">Z").workplane().center(1,1)
.box(2,2,2, centered=(1,1,0)).faces(">X").workplane()
.box(1,1,1, centered=(1,1,0))

But this does not work, the .faces(">X") applies to the whole object, not the box222 on the top. I get this:

Ultimately, I want something like the following with multiple objects built on the platform:

.box(5,5,1, centered=(1,1,0)).faces(">Z").workplane().tag("platform").center(1,1)
.invoke(add_canon())
.workplaneFromTag("platform").center(-1,-1).invoke(a_different_canon()).

I don't see any way to do this without just calculating positions and putting hard numbers into .transformed().

Seems like this should work (with a call to .end()) but it doesn't:

.box(5,5,1, centered=(1,1,0)).faces(">Z").workplane().center(1,1)
.box(2,2,2, centered=(1,1,0)).end().faces(">X").workplane()
.box(1,1,1, centered=(1,1,0))

Also notice I'm not building on top of the box222 but in front of it, so faces(">Z") is definitely not the right answer.

Is there some useful selector or tag I'm overlooking? Thanks.

[adam-urbanczyk]

With the current API I'd do it like so:

import cadquery as cq

res = (
        cq.Workplane()
        .box(5,5,1, centered=(1,1,0))
        .faces(">Z")
        .workplane()
        .center(-1,0)
        .box(2,2,2, centered=(1,1,0))
        .faces(">Z").siblings('Edge').faces('>X').workplane(centerOption='CenterOfMass')
        .box(1,1,1, centered=(1,1,0))
)