Printable Mendel Y axis

I've been slowly tweaking dissidence's printable Mendel frame, and I think I'm not far from something useable. I started thinking about what's next, and thought a rail and wheel might work for the Y axis, so I made this! Its supposed to be an upsidedown T rail with tab&slot to chain the pieces to make longer rails, and three wheel pieces that go together to sit firmly on the rail.

Yeah, its not so pretty. When you print 3 small wheels like this, the stringing between them is so bad that when