Thanks for the advice,
...or you are tapping the portafilter before leveling. Dont tap it...
Yeah, I had been tapping the pf quite a lot whilst dosing (I never used to do that - weird how bad habits slip into your technique under the radar), and have reduced this to one tap mid-dose. This has enabled me to fill to the rim of the basket, tamp, and lock okay.
If you have a naked pf and notice you're getting "donuts," make your grind finer and your tamp lighter
I've developed a problem with center-channeling: about mid-way through the pour, the extraction becomes quite thin from most of the basket (to the point that you can see some of the holes in the filter basket) and fast-blond through the middle, or slightly off-center. I've never had a channeling problem before. Off to re-examine my WDT....
DC