Dave, ever make bread dough? When the dough is too wet it sticks and pulls when you try and cut it. When it is dry enough it cuts cleanly. Wood works much the same way. Pine is full of moisture and resins, both things that encourage tear out. In a perfect world we would all have wood that is nicely aged and naturally dry enough to get excellent results every time. In the real world there are steps you can take to ensure better results. Here are some general ideas that should help: Make sure your bit is clean and sharp; remove any resin build up with a solvent such as mineral spirits; examine the cutting edge for nicks or dull spots. Run a small bit like this at top speed using a steady motion as you pass the wood over the cutter. Try Ed's idea of making a straight cut first to remove the bulk of the wood, then follow up with your dovetail bit.(This is the same as making a rabbit cut in multiple passes so no more than 1/4" is removed at a time.) To reduce tear out use a backer board. This is just a piece of scrap used to push your wood across the cutter. It gives support so the wood is less likely to chunk away. Give your wood a chance to get used to your shop before working with it; a couple weeks is a reasonable rule of thumb. Remember that no matter how careful you are, there is always that piece of wood lurking out there ready to twist itself out of shape when you show it your cutting tools.