[shawn1231]

Our team just finished our screw prototype. We, instead of making a "bearing" big enough to hold the PVC, drilled a hole in a flat cap and put a bolt through it which we then put into a piece of wood at the bottom with a hole big enough for the bolt. It worked for our prototype but I would highly recommend doing something similar. Not only is a bigger "bearing" going to be hard to find, or make, but you probably have some bearing in the shop you could use to fit a bolt.

Also about the compression, I think you will find that you are compressing the balls way too much. Aside from the pipe bending or whatever other problems this creates it's just not necessary. Our team finished our screw on Saturday and with no compression at all it works quite well.

I'd like to know the diameter on your center shaft and what exactly you have prototyped so far. I mean how have you actually implemented the screw, because I know the concept and how we did it but it is likely you did it completely differently.