The recommendation is 3 teeth engaged with the work at all times. Bandsaw blades begin to fail when fewer teeth are engaged because the depth of cut for a given feed pressure increases rapidly, putting all that strain onto a single tooth. Once that tooth shears, there is a gap in the tooth pattern that allows for a feed increase again, and they begin failing like dominos.
14 TPI is a tooth every .071". I've gotten 14 TPI blades to last, but knowing the information above, I know not to feed very hard and just let the saw do the work. But 14 TPI should really only be used for .22" or thicker stock.
18 TPI is .055, so .165" stock minimum.
20 TPI is .050, so .15" minimum
I've been using 30 TPI blades lately, .033 per tooth, so cutting .093 and up is no problem. I've cut .060 with them as well. Once you get to a certain TPI, the height of the tooth becomes so small the teeth are inherently stronger and can accept almost all of the load you give them. These 30 TPI blades have lasted just about forever compared to others I've tried. They are a little slower.
20 TPI I think is about the most reasonable compromise for most makers, and just understand you shouldn't ram 1/16" thick stock into them as fast as it will go, where you could do exactly that with 3/16" material.
