Was he making good lams, and then something changed, or has he been having this problem from the start?
This is going to be hard to troubleshoot without more info, and without actually being there to inspect his machine and see how he's doing it. There are just so many variables.
I'd check to make sure nothing came loose, all bearings and bushings are good, check feed rate and the amount of material he's trying to remove. He might just have to slow the feed rate and take less material off each pass. What grit paper is he using?
Also make sure the lam isn't slipping on the sled, the sled isn't slipping on the feed belt, the feed belt isn't slipping on its drive roller, and the drum drive belt isn't slipping on a pulley, etc... could be lots of things bud. I'm just throwing some things out there, I've never had wavy lams, but my machine is a little different than yours too so, maybe some of this doesn't apply, but those are the sort of things I'd be looking at first.