In my experience if the spindle and board are too soft they tend to reduce each other to powder before getting hot enough to produce good coals. Slightly harder wood seems to work better. On the other end too hard a wood can build up a lot of heat but fail to drop a coal.

The wood, of course, is best very dry. Slightly green or damp wood can make things much more difficult. You have to generate enough heat to drive off the moisture before you can start to get near ignition temperatures.

Irony is that drying the spindle and board over a fire makes them work better. Kind of like needing a flashlight to change batteries or downloading a better driver to get the PC to run. Bootstrapping has always been an issue. I knew a Boyscout leader who would use a blow-dryer to prep his bow-drill setup before demonstrations in a damp climate.

i once saw a film where a guy in Canada got dropped off in the brush by a chopper and did a survival camp as part of his PhD thesis.he busted rocks to get tools to make the parts for the bow drill and said it was a all day process to get the thing together and working.he never let the fire go out for the month or so he was out and said it was so much work that anyone who had to do that would never forget his matches again.he was a pro,like the guy who did the Ikea fire drill or those "natives" i see in the "how they live" Anthro movies.i would suggest that if you want to get the knack on how to do this that you make the best set you can and try it out every day--every day..maybe while watching some mindless TV you can work the bow to get the idea of how much pressure you need to exert on the spindle--and so on--be a kid in a pre-modern world who needs to learn to make a fire and not a guy who is just fooling around to see if it will work,if you really want to use it as a survival tool.i also saw another film from Canada made in the 50's where a native guy takes nothing more than a big splinter of pine and works it--fast and hard--in a grove in a split open pine block and gets a fire.i assume he grew up learning how to do that so it was second nature.
sorry..another 1:30 AM run-on...maybe the best survival item for fire making would be a tiny surgical implanted sparklight stick you could cut-dig out of your leg when all else failed.

IMO I think that to just have the knowledge, confidence, and ability to be able to create an ember is a major undertaking itself. Do I plan on getting dropped off in the middle of no-where, nope not in my immediate future. However I do spend a considerable amount of time in the outdoors and if I did need this ability I would feel better about knowing I can atleast or I have in the past created fire.
I do think that in a survival situation to actually think you will just grab up some materials and make yourself comfy, is not likely to happen. There will be a good amount of "suck" involved with it. However to have the self confidence of being able over time if need be fend for yourself and survive as comfortable as possible will increase your chances down the road.
Same for me just rattling on early in the morning at work.

"KEEP UP THE FIRE"

Keep on preparing! It is often true that: opportunity + preparation = luck.

I recall the stories of native americans coming upon starving and sick settlers, not even conceiving those folks could be sufffering such things, because all around them were wild plants for food and medicine. One sad but classic case was wagon train members suffering from scurvy that could easily have been prevented and cured by tea made from the needles of the pine and other conifers all around them.