I just replaced the cast iron fork that holds the belt-interrupted air supply and the air supply nozzle itself on my Bridgewood 16" open end wide belt sander. This machine is similar to the Sunhill and Powermatic and probably several others. I used a Powermatic replacement part for the fork that's similar but not quite identical to the unavailable Bridgewood part. The air supply nozzle I jerry-rigged from an off the shelf fitting using the same very small nylon pipe for the actual air delivery. I'm now unable to get any belt oscillation, and I don't understand how it's supposed to work well enough to figure out what to try next. I've always assumed the belt blocks the air flow across the fork and either the blocking or unblocking of the flow of air (which, or both?) precipitates a rocking action in the upper drum that causes the oscillation. Should I be able to see this rock happen in the drum even without a belt in place? Might the air flow not be straight enough.....Any suggestions on how to diagnose this? Thanks!