Ken, the scale was just printed at Staples on their large format printer. After roughing a sheet of clear acrylic with sandpaper, I spray-mounted the scale on (after I had trimmed it out into a circular ring). I put several coats of polyurethane on it, routed the shape out, hand-sanded the edges smooth, and then painted the exposed acrylic with satin-black enamel on the top and outer edge.

There's no need to lock the scale. It has no contact with the scope itself as it sits outside the diameter of the roller bearings by a couple inches. It's a ring and I have a triangular arrangement of 3mm cylindrical stops that the inner edge of the scale rides against. My routing must have been off a little as it doesn't rotate perfectly smooth (like butter), but "catches" in areas and there's a little more friction. I suppose I could make the stops abrasive and they'd wear down the high spots over time...