Moisture meter accuracy?

[Stephen1]

Long store guys and I need some thoughts on the moisture meters accuracy.
I dried Some very Large "Burr" Oak slabs for a customer . 3"x36"x10' They had been abused before I received them, left in the sun, not stacked and stickered  properly.
I put them in my kiln at around %24 moisture , added a couple of buckets of water to the floor and didn't drain the kiln for 3 days allowing the moisture to soften the potential case hardened surface.
I ran the kiln normal after that 160 and 24 drain cycle. The water stopped coming out  after a week . My Delmhorst showed -5.6 to %8.9 moisture in these slabs. I write the date and % on the slab with a circle around the probe marks.
Now here it comes, this is around the time of my problem with my hammer probe . Called delmhorst for trouble shooting. I needed a new hammer probe or send mine in for service, I ordered a new one, while I tried to fix the one I had.
The customer took the slabs to have them planed and after doing 2 slabs  they would not plane anymore. Complained that vacuum kilns don't work . The following are pictures he sent me of the planer guys moisture meter readings.
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<bHere are the pictures of my del  r>
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Here are the pics on my Delmorst with the new hammer probe and properly calibrated with the help of Delmhorst trouble shooting 
The 1st pic is a probe into the side of a slab and the next is a probe into the centre of the same planed slabs  (from the bottom as it was on the forks) >
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I told the guy to bring the slabs and I will dry them and I also gave him a credit of $150 towards future drying or blade sharpening.
The next are my Delmhorst set to White Oak with the new Hammer Probe and the calibration was checked with the help of Delmhorst.
Why such  a Difference?
Is there such a difference between White Oak and Burr Oak? I do not think so.
Is the planer guys meter out that much?

[boonesyard]

I'll be standing by to see responses here, but I've had the same trouble with my Delmhorst slide hammers. I have two of the meter/slide hammer kits and both of the slide hammers or connections to the meters don't work properly. Looks like others have had the same issue.

[petefrom bearswamp]

I just got 450 bd ft of 4/4 ash from my kiln guy.
It was air dried to 12-13 percent.
He has an older analog delmhorst hammer pin meter.
He read 6 percent after drying.
I cut into the center of one board and checked it with my mini pin meter which only goes to 6 percent and it showed 6.
I tried one of the pinless ones, I cant remember the brand and it was way off per my little one.
sent it back.
I suspect his pinless was off too as his reading approached that of green wood.

[Stephen1]

I'll be standing by to see responses here, but I've had the same trouble with my Delmhorst slide hammers. I have two of the meter/slide hammer kits and both of the slide hammers or connections to the meters don't work properly. Looks like others have had the same issue.

I redid the connection on the cable to unit  with new connector, p59 and solder, tested it and it was good so I suspect the hammer or cable as being faulty. 

[Don P]

I was getting flakey readings from my old analog slide hammer. Smearing dielectric grease on the connections to the unit and the pin connections fixed that.

[Stephen1]

I'll try that tomorrow on the pins. 

[Walnut Beast]

Did you try your pins on your unit also to compare to his surface reading

[Stephen1]

My short pins showed the same as the deep pins, 9-10% 

[Larry]

A confidence builder is comparing your readings to oven dry samples.  I have both a Wagner and a J-2000.  They never read the same with the Wagner usually a little higher.

I also struggle with the thick stuff as I don't do oven samples with wood over 6/4.

[customsawyer]

I don't have all of the answers but here is a few things I'm seeing. First off if it was case hardened then it may take more than one introduction of moisture (and some chickens) to get it to open up and release the interior moisture. This is what they are finding after planing. Second, in the last couple of pictures the J-2000 looks like it is in sap wood and towards the end of the board. Sliding hammer placement in sap wood or towards the end of a board will usually read dryer in big slabs than the heart wood where it looks like the Wagner is placed. Lastly one of the main reasons I don't have a Idry kiln is they seem to struggle with drying oak. There is a couple of them not to far from me and they both have a hard time getting even drying in oak. I've had one bring me 4/4 white oak to plane and it would vary from 8% to 23% at different places in the same board. The one time I have talked with Jim way back when they were first coming out he even said the Idry struggles with drying oak.

[Stephen1]

Custom Sawyer, I agree with the oak, not so much the RO but the WO and the Walnut I have had troubles in the past. And all my troubles in the past are usually in thick walnut and WO slabs. I go back to what the Gene talks about , these type of trees picking up a bacterial infection. A gel is formed in the wood and is hard to get it to release. Maybe?
Maybe the surface meter shows more problems or higher moisture in some locations, is because you can test more areas without damaging the wood, where the probing is limited. I do not tent to poke a lot of holes in the wood. I judge a lot by how much water is coming out of the wood. 
I am not sure the problem of drying of these thick slabs is related to Vacuum Kilns. The idry is really just a heat kiln under partial vacuum, Versus the RF Vacuum kiln with its  zero vacuum and radio waves bouncing through the wood, It tends to heat up the knots in the wood more than the rest of the straight grain wood, like good quality lumber 

[customsawyer]

I had some cypress slabs one time that the customer wanted in a hurry.  Cypress is normally fairly easy to dry. I sawed them and stuck them in the kiln green off of the mill. They locked up at 30% moisture and would not let it go. I tried running the heat up and they still wouldn't let it go. Pulled them out and let them set for a month, then back in the kiln. Still locked up. Ended up letting them air dry for 8 months and then put them in the kiln. They were done in 15 days. Some woods will just stall on you no matter what you do.
As to the pin holes in the slabs. I always use the same holes every time. The individual that is finishing the slab should be able to fix a couple of holes with out to much extra effort. I also try to have the pins in different growth rings. Test some in clear areas and some close to knots. I keep a eye on how much water is coming out of the kiln and what my RH is inside the kiln. The easiest way for me to check the kiln is to open the walk in door with my sun glasses on. If they fog up we still have moisture in there. This doesn't help if the wood stalls out though. That is what the meters are for.

[Stephen1]

I was always under the impression that we could not use the same holes as the wood in the holes would dry out faster.