Drying blanks

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Gary Beasley

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Sep 18, 2009
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Marietta, Ga. USA
Has anybody ever tried this trick? You put your blanks in the oven to dry them, get them all evenly up to the final temp, then dump them all into the empty vacuum tank while hot and hit the vacuum. Seeing how the boiling point of water drops with the vacuum the hot blanks should boil off the residual water a lot faster in the tank at full vacuum. Of course you will need something on the bottom and sides of the tank like some corrugated box board to keep the heat off the plastic. Anybody see any drawbacks?
 
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One drawback might be that the hot steam vapor may damage the vac pump if it's something you do regularly. Or maybe the rapid de-moisturizing could cause the blank to crack and split? I think I'll just stick to microwaving!
 
Let us know how they come out.
I use an old counter top convection oven with dehydrator temp setting. They dry out nicely without cracking, but must be stabilized before making pen. I found out the hard way.

Russ
 
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I have some cocobolo that I got from Alton that I am going to put into the oven for a few days so I can try it out. I just ordered 16 Jr. Gent 2 and 4 Jr Statesman from CSUSA and would like to segment some of it into these pens. I also got some more Atrax pens from Exotic. I will be very busy again soon. I hope.
 
I finally got my tank cleared and tried this on some Kwanzan cherry. Since I had my little oven calibrated and controls taped down at 200F I figured that would do just fine. first I tried baking the blanks for a half hour then put them in the tank. Immediately the water started condensing on the sides of the tank and running down. This was a good sign and I was prepared for it with bent wire spacers under the blanks to get them off the bottom and I was careful to stack the wood away from the sides. I gave it about a half hour and took them out. My Ryobi moisture meter read up in the 23 percent range, higher than when they went in. I'm thinking that meant the water was migrating to the outside but not finished. Back in the oven for another 45 minutes then another half hour in the tank. A fraction of the amount of water this time and the meter read a solid 10 percent so I'm happy with it. I'd think denser woods will take longer to migrate all the water out but shouldn't be much more trouble.
Let me know your experiences with this if you try it.
 
RMayoIII said:
One drawback might be that the hot steam vapor may damage the vac pump if it's something you do regularly. Or maybe the rapid de-moisturizing could cause the blank to crack and split? I think I'll just stick to microwaving!
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My experience with microwaving involved scorched wood or way too long drying times. It would be nice if we could combine vacuum with microwaving to get the best effect overall.
As far as the hot steam, theres not enough of it to cause problems, especially seeing that most of the water vapor condensed on the sides of the tank.
 
200 is really harsh to start drying wood. I think water boils in a hard vacuum at 90 degrees, so would start with way lower temps. Crotch wood and burls, will not take that kind of temps unless they have air dried for a long time. I also hate to use all that energy. I dry my wood on top of the main trunk line off my furnace in the winter, and house attic in the summer.
 
low_48 said:
I think water boils in a hard vacuum at 90 degrees, so would start with way lower temps.
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Water will boil at a much lower temp than that in a deep vacuum. Here are some numbers. These are based on sea level so will have to be adjusted based on elevation. To adjust for your elevation, find out what your elevation is (search wikipedia for your city), then use my new Maximum Theoretical Vacuum calculator I just put on my website.

at 27.75" Hg (92.74% vac) water will boil at 104° F
at 28.67" Hg (95.82% vac) water will boil at 86° F
at 28.92" Hg (96.66% vac)water will boil at 80° F
at 29.02" Hg (96.99% vac)water will boil at 76° F
at 29.12" Hg (97.33% vac)water will boil at 72° F
at 29.88" Hg (99.87% vac)water will boil at 6° F (pretty easy to do with a good pump and good chamber)
at 29.9195" Hg (99.99% vac)water will boil at -70° F!

The thing to remember is that the typical dial vacuum gauge is not completely accurate. The gauges I use are +/- 1.5% over the range of the gauge. However, I have an electronic, digital vacuum gauge and have been able to pull a 1,000 micron vacuum in a chamber which equates to 29.88" Hg at sea level. At this level, water will boil at 6° F!

So, basically, if you have a good pump and a well sealed chamber, you can easily boil off the water in your wood. However, at room temperature, it will take quite a while to boil it dry. Heating up the blank will certainly cause the water to boil off quicker.

I just find it much easier to throw my air dried blanks in the oven at 200°f for 24 hours. This assures they are oven dry or 0% moisture in all of my testing. If the blanks are already air dried and at equilibrium moisture content (approx 10-11% around here), I have not found any degradation at 200° for 24 hours.

For green wood, I use a lamp timer and still set my oven at 200°. I set the lamp timer to run for 30 minutes, then off for 30 minutes. I do this for a day. Then I go to 1 hr on, 30 minutes off for a couple of days. Then 2 hrs on, 30 min off for another day. Then full on for 24 hours and get very little, if any degradation in most woods. Of course this is for blanks that I am going to stabilize which I want to be 0% moisture.
 
I run the tank on some oak burl tonight that was very wet when I got it but had dried down pretty good in the last severAl months. I've finally decided a one hour cycle works pretty good, one hour in the oven, one in the tank. After I pulled it out of the tank I got my moisture meter after it and this thing is usually way sensitive. I could barely get it to register on this stuff. First time I've ever had it do that to me. I think this will do me some good.
 
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