Provide a thicken method for Shell

[lorenzncode]

trafficstars

import cadquery as cq

lines = cq.Workplane().lineTo(10, 0).lineTo(20, 4)
lines = lines.consolidateWires()

path = cq.Workplane("XZ").lineTo(0, 10)
result_sweep = lines.sweep(path)

# Shell: result.sweep.val()
# thicken not supported here
result_thicken = result_sweep.val().thicken(0.2)
result_thicken = result_thicken.clean()

show_object(result_thicken)

[adam-urbanczyk]

I guess you want to move Face.thicken to a hypothetical Mixin2D class?

[lorenzncode]

Yes a new Mixin2D class sounds good.