While current RepRap implementations can print any arbitrary 2D shape on the first layer, they have "unsupported material" overhang limitations that make it impossible so far to print some 3D shapes.
Some designers find it interesting to work around this limitation, and build useful and amazing things (such as new RepRaps) by either (a) keeping them within the limitations of the machine, or (b) slicing them into smaller parts that are each within the limitations of the machine, and then attaching them together.
Other designers chafe at the limitations, and desire some way of temporarily supporting the part being printed, making it possible print *any* conceivable 3D shape within build volume and resolution limitations.
There are 2 automatic ways to support the desired part:
- Main page: Support Extruder.
In the (hopefully few) locations that need support, build up a support pillar under them using material extruded from a Support Extruder.
powder bed printer
- Main page: powder.
Completely fill the build volume with the raw material in powder form, one thin layer at a time. After each layer is placed, selectively "mark" all the regions that are conceptually "in" the desired part, using superglue or lasers or something.
After the build volume is completely filled up to the top of part being printed, pour out and recycle the raw material that is still in powder form. The desired part is now a solid mass composed of powder grains bonded together.
It is also possible to insert support material manually during a print. See Manual Support.