In my experience the cracking almost always happens during the tip profiling step. The blade on the underside of the large metal plaque that the reed is inserted on for profiling is the one which cracks. While the top blade is being profiled, the bottom blade is cracking.
|the devastating sight of a cracked blade when the reed is turned over after tip profiling the other blade|
This does not indicate a flaw in the tip profiling machine, though. (I highly recommend using a tip profiler!) I suspect that the cracking is most likely caused by not soaking the reed long enough before insertion onto the plaque. Also it seems that when I'm impatient while making reeds, I'm much more likely to end up ruining the reed. I've been known to become overzealous with the knife during the shaping step with dreadful results, for example.
Although my reeds rarely crack, today was one of those days. Today's cracked reed could have been a victim of not enough soaking (it was soaked for maybe 5 minutes) before tip profiling, and I was definitely in a hurry (which is why I only soaked it for 5 minutes!).
It's time to slow down, take a deep breath and get back to the drawing board......and remember:
Don't make reeds when you're in a hurry!