[DampRobot]

The most I've seen box tubing run over in the 2" dimension is around .003", and about .002" for the 1" dimension. (Inside dimensions are another story.) That's pretty high precision, I doubt most students could get similar precision on a manual lathe between two of those snap ring grooves.

While the box tubing per se is fairly high tolerance, once you start adding in other parts on the shaft, the tolerances really do start to stack up. As Travis said, line to line with something like snap ring grooves tends not to work very well. Instead, it's a good idea to add in a bit of wiggle room in the form of a small adder on the groove-groove dimension.

If you don't need to do two snap ring grooves, my team's used a slightly different solution which soaks up tolerances on the shaft stackup quite well. We put one snap ring on the shaft (this year, it was on the inside) and on the other end of the shaft, we tap a 10-32 hole. A screw in this hole with a few washers retains the wheel, and nicely soaks up any inaccuracies in the box tubing, bearing blocks, etc.