Here's the trick: you drill a pocket in your soft base with the tip of your knife, and you shape the tip of the spindle to fit that pocket as close as you can. This gives you a lot of contact area (friction) when you start bowing. You also want to carve a little channel from the pocket in which to place your tinder. If I recall, I've gotten a nice flame in as little as 5 minutes or so. If you've done well (and you're bearing down on the top block as you bow) you will get smoke in just a couple of minutes, but you will not get flames unless you've got good-quality tinder adjacent to the pocket in the bottom block. It helps if your bottom block is soft, dry wood, and can easily deform to the pressure of the spindle, giving you the maximum surface contact and friction. Soft white pine and cedar are really good choices, here.
The optimal choice is VERY hardwood for the spindle, VERY soft wood for the base (where you want to build the fire), a relatively hardwood for the top block (to reduce friction), and the selection of wood for the bow is "whatever". It is very easy to get a fire going with this technique if you have collected some good tinder. Some good tinder might be sun-dried peat, leaf duff, lichens, etc. There is a lot of stuff that can be found for tinder, even when it is cold or very wet - you just have to know how and where to look.