We've been having problems getting our Bocote and Cocobolo to finish up nicely. We're using pretty small pieces of wood, around the size of a pen blank after it's been narrowed to a half-inch or less - it's mostly pieces for my wife's hair jewelry, but I'd been hoping to use some dark cocobolo to make the black pieces for a chess set as a gift to my brother also - not as dark as ebony, but much prettier I think.

However, it'd be a bit pointless if I can't make the wood coat nicely, and these two are proving to be a real pain. As was recommended to us before, we're using two coats of dewaxed shellac followed by two to three of oil-based polyurethane (satin or gloss) as the outer coat, sanding lightly between coats. To coat, we alternate between the piece standing vertically (mounted on a small pin, using a hole drilled into the base that will be covered later) and hanging the piece so that it is upside down instead. We need to use a coating that is fairly resilient, and yields a waterproof finish.

But we're finding, sometimes, that even after it seemed to have dried nicely on the previous coat, it then gets sticky with the next. Right now, we have a piece that was almost dry last night, with just one small sticky spot that had not quite cleared up - today, the sticky spot is bigger. It doesn't happen with every single piece, but I'd guess it happens at least 75% of the time.

Is there anything we're likely doing wrong, or anything different that people have used to coat these woods without the coatings turning sticky?