[Woodcarver] drying a 10" log

[Lynn Diel]

Ray
To follow up on what Phill wrote, there is an article
in the woodcarver ezine located at the following url;
http://carverscompanion.com/Ezine/Vol2Issue4/Vol2Issue4TOC.html
it talks about how you can build your own vacuum kiln.
If you have any questions, let me know.
Good luck Lynn


--- Phill Pittman <phill at masterwerkes.com> wrote:
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> 
> Hi Ray.  there is no simple way ( if drying the wood
> ) to prevent splitting
> without involving an environment with a partial
> vacuum in it. We carve large
> ( and small )green wood regularly and anything you
> do that accelerates air
> flow past it will cause cracking where the air
> crosses the surface. (
> aromatic cedar and a few imported oil laden woods
> are some of the only
> exception ). drilling holes will help if naturally
> drying, but hurt if you
> force air with the vacuum.
> 
>  Making a vacuum chamber for a log is not as
> difficult as it seems.Large
> schedule 80 pvc ( the kind you will see around
> public sewer projects ) will
> work in a pinch, but if it is something you might
> want to repeat later, a
> section of iron pipe that the log will fit inside of
> will do it. I got mine
> from a local scrap metal place and had enough left
> over for the " shop"
> smoker/bar-b-q). Welding a plate over one end and
> fashioning a removable
> plate for the other end will work for the vacuum.
> remember a vacuum is self
> sealing and getting an airtight seal is more
> important than fasteners or
> bolts etc. It is also much easier to do. If your
> project allows, remove any
> surface of the wood that you can before drying, but
> keep the fresh cuts wet
> until you are putting it in the tube.
> The fluids inside the log will gasify at near room
> temperature in a 25"
> vacuum. If you are lucky enough to score a good
> vacuum pump, it will work at
> room temperature.
> As I am sure you know, wood splits when drying as
> air removes moisture from
> one location more than the rest. Usually this is the
> exterior of the wood.
> The resulting shrinkage from the loss of moisture is
> unable to occur because
> the interior wood still contains it moisture and
> it's original size. When
> using a true ( partial) vacuum to remove moisture,
> the wood is not drying
> from the outside in. As the pressure drops the
> moisture, in a pretty uniform
> sequence, aspirates the moisture into gas which
> escapes the wood.
> 
> This process is accelerated by heated wood. This is
> the only difficult part.
> There are expensive heating blanket made
> specifically for vacuum kilns, but
> they represent a significant invest in the make-up
> of the chamber and the
> heater itself. Any heat source has to be contact
> only. Remember that a
> vacuum insulates and normal convection does not
> convey heat. Radiant heat
> ( light in various forms ) heats only the exterior
> and may cause uneven
> drying. All we do is pre-heat it just like an oven
> and try to get the vacuum
> pulled down while there is still some heat in the
> log. It will not cool down
> much after the vacuum has removed the air.( think
> about a thermos jug ) When
> you heat it up you have to let it remain heated for
> several hours to insure
> that the interior of the log is the same temperature
> as the exterior.
> 
> You can get serviceable vacuum pumps off eBay for
> $50 bucks if you are only
> going to do it a time or two. The actual original
> purpose of the vacuum pump
> is inconsequential, only that it will pull a 22" or
> better vacuum and run as
> required for several days. the drying time will
> depend on species, size, and
> too many other factors to name. But the thumbnail
> measuring method of choice
> is to weigh your entire contraption. If your log is
> of any size there will
> be a drastic weight change ( usually a hundred or
> two pounds) as it loses
> moisture. When your assembly stops losing weight,
> your done. At lest as far
> as you can go without mortgaging the house.
> Commercial kilns dry 8/4 white
> oak for about 48 hours at 22" vacuum. Almost zero
> checking /splitting and a
> very uniform 6% moisture content.
> 
> Woodmizer ( the same folks that make the saw mill)
> used to sell some light
> commercial vacuum kilns and are a great source for
> technical info.
> 
> All that being said, if you can find it, aromatic
> cedar is real forgiving
> the same day it is cut. We are in the middle of a
> 2000 piece run of
> "spirits" about 20" tall and 4" thick through the
> nose area. We produce
> about 50 a day out of aromatic cedar that is often
> sawmilled on the same day
> we mount it on the machines. We have an occasional
> loss from internal
> checks, but they seldom to appear to be from drying
> in the wind of the
> router motors, more like internal stress cracks with
> some resins visible.
> 
> I also have a friend that is about to try Vacuum
> bagging a log just like you
> were gluing laminate and putting to in a hot box in
> the sun. I will be
> curious to see how it comes out. In theory it should
> work the same.
> 
> And as said in the previous post, if you can stress
> relive the back, that is
> always going to give you a more long term stable
> product.
> 
> Sorry for the oration, I get asked this from time to
> time and just hadn't
> had a forum to share it on.
> 
> Best of luck and let us know how it goes.
> 
> Phill Pittman
> digicarve at verizon.net
> www.masterwerkes.com
> 
> ----- Original Message ----- 
> From: "RAY MIGHELLS" <raymighells at earthlink.net>
> To: "[Woodcarver]" <woodcarver at six.pairlist.net>
> Sent: Monday, June 21, 2004 6:31 PM
> Subject: Re: [Woodcarver] drying a 10" log
> 
> 
> > To make a DONATION to the Mailing List using
> PayPal OR regular mail, click
> this link:
> http://wwwoodcarver.com/WWWList/WWWList.html
> >
> > Hi Ray;  What kind of wood?   How dry is it now? 
> What are you going to
> > carve on it?  Many woods are easier to carve
> "green".  Keep it wet with a
> > spritz bottle of water, cover it with something
> wet/damp, and wrap in
> > plastic when not carving.  Depending on the depth
> of your carving,  you
> may
> > have to hollow it out from the back.  There's a
> lot of grain tensions in
> > different degrees of stress,  so even if it is dry
> when you are finished,
> > the seasonal changes can have distastrous effects
> if the tensions are not
> > somewhat compensated by relieving the back.  A PEG
> treatment will help
> some.
> > Happy carving and good luck  Ray Mighells  6760 Rt
> 417 Killbuck NY 716 945
> > 0098 Please view my work at: 
> http://www.picturetrail.com/razaxnstuff
> > ----- Original Message ----- 
> > From: "Fishley, Ray (IS - Municipal Engineering)"
> > <Ray.Fishley at City.Saskatoon.Sk.CA>
> > To: <woodcarver at six.pairlist.net>
> > Sent: Monday, June 21, 2004 5:27 PM
> > Subject: [Woodcarver] drying a 10" log
> >
> >
> > > To make a DONATION to the Mailing List using
> PayPal OR regular mail,
> click
> > this link:
> http://wwwoodcarver.com/WWWList/WWWList.html
> > >
> > > I would like to carve a 10" x 12 foot log.
> > > I am looking for away to dry it so that it does
> not crack or check.
> > > I was thinking of drilling a 1" hole through the
> center of it and
> > connecting
> > > a vacuum to it for a few weeks.
> 
=== message truncated ===


=====
Lynn E. Diel
Columbia, MO
Website: http://carvers-creek.com