Most of the materials used for 3D printing are either moisture sensitive, moisture absorbing, or both. We all know it, and we try to deal with it as best as we can. But sometimes it bites you anyway. Here in San Jose, CA it actually rained the other day. That's a big deal around here, what with the drought going on. So while the rain was welcome on its own merits, it also provided a good learning opportunity. And, of course, all of the frustration that comes with learning things the hard way.
The humidity here got up over 70% while it was raining and stayed that way for most of the day. That entire day, I couldn't get anything to print. The powder looked funny while it was sintering, it curled and 'spiked' like crazy, and just wasn't spreading right. It looked a lot clumpier than normal. I tried running the powder through the sieve again, which helped a little, but not enough.
Since then I've been paying more attention to the humidity while I'm printing. This morning the humidity was over 50% and I was again having problems with the printer. Some time after noon, it got down to 45% and suddenly I could print again. Right now (almost 1am) the humidity in my house is 42% and the print I have going is looking pretty good.
So, lesson learned. Keeping your material dry isn't enough. You also have to keep the air dry. Or at least keep it below 45%. Now how am I going to do that?