OK, so here is what I did. I did a microwave test as per Lamb as I did not see Gene's instruction until just now. I only have a scale that weighs to nearest gram, but I used it anyhow. And I used the microwave at 30% power until the net weight stopped dropping for 3 cycles. My final weight was 176 grams. Start weight was 187 grams. Interesting thing about the ligno is it read the oven dry wood at 4.2% MC which is one of the spurious readings it gives me all the time (its zero for a bad reading I assume) , but I can't get any more weight to come out of the samples, so they are oven dry or darn close. I ran them about 3 minutes out of the gun and about 15 cycles of a minute each after and weighed the set each time until the weight stabilized at no change for 3 cycles. So, the final calculation of the MC of the wood would be 6.2% Almost bizarrely low for air dried stack subjected to heat and fans for 2 weeks only, but it is Minnesota winter. It was a top piece; the bottom pieces might be higher MC%.
Ligno readings prior to test 9.5% typical at 100F (edge readings only), control outside of hotbox was also 9.5%, but was at 70F, so the control MC was higher (but I was too ignorant to realize the 2% heat factor). The edge readings were probably not as accurate as an endcut, but I have found them to be close-maybe not anymore for wood that is running below 10% to start.
I shut off the chamber yesterday since it didn't seem like I was pulling any water out of the stack. I checked two boards today and got 6.8% in all cuts (end grain readings), so that is pretty close to my microwave test and pretty close to my correction for heat above. My air dried sample piece is also pretty dry on end cut tests, but running at 8.1-8.5%. That board never went into the hotbox.
I'd say the lumber is dried well enough to use and I was getting some errors in the ligno due to temperature conversions that I forgot about, my edge readings vs endcut readings, and due to the battery issues earlier. I used it before on green lumber and never even worried about any of these things.
If I try to drive more moisture from the samples, I'm guessing I'd be able to get another gram or two or 1%, so I might not be technically oven dry, but it is close. I'd rather not destroy our $1300 microwave in the process, so I could also just run them in the real oven overnite on low and might just for fun.
I guess the only question for the group is does it seem rational that I would have had air dry lumber at 10.5% mc in November in Mn (recall the battery and edge readings might have been causing some error), and then the lumber got planed and sat in the building and came down to 2% mc or 8.5% in Minnesota winter (my control piece reads 8.1 to 8.5%), and bringing it into a 100 degree dry fans climate for a couple weeks dropped it to 6.8-7% and the moisture just went into the plant/space? And would the 7% MC explain why I was unable to drive any more water from the stack at 110F?
Thanks, sorry if I'm an idiot; I don't do this everyday.
I'd say the lumber is ready to use and the reason I can't get moisture out of it anymore is because I'd need to heat it to higher than 110F and don't need to do so.
Thanks Gene. Your wisdom was very helpful to me.