The clearances don't tend to be all that big since most good part cooling ducts surround the nozzle. That said, many higher end hobbyist printers have the abili

The clearances don't tend to be all that big since most good part cooling ducts surround the nozzle. That said, many higher end hobbyist printers have the ability to physically tilt the bed/gantry, which would allow for true non-planar printing accessible to a large number of people with just appropriate gcode and slicer improvements. Edit: Actually, come to think of it, it's common for the front to remain open, for easily viewing the nozzle during printing. So non-planar prints should be possible on pretty much any printer in the y axis at least.