The frame needs to be a flat base that you can mount everything on horizontally and a goose neck of some kind to hold the Z axis (the up and down part with the motor tool)firmly in place. I used one inch pipe just for fun but as it turned out it was pretty handy too. When I needed to make adjustments I could just tap it with a hammer. As you can see the post that holds the Z axis doesn't have to be in the center. It just needs to be firm and the water pipe does a good job of that. Later, after you are sure all the pipe joints are in the right place, you can add a drop of thread sealer to the joints and it will be a good solid structure.