The various discussions on ways of drying wood prompted me to post this message.

The following article was published in the March 1998 issue of More Woodturning.
I authored the article with technical help from Gilbert Brown of Omak,
Washington. Gilbert had done considerable experimenting with his process and was
trying to market the system with little success. I wrote the article and
submitted it to Fine Woodworking. They kept it for a year and then returned it
saying that their experts said it would not work. I leave it to the reader to
determine whether this might be useful.

I first met Gilbert Brown at the 1993
“Art in the Park” craft fair at Omak,
Washington. Several of the bowls on my
table were turned from wet wood and
had warped appropriately. Gilbert said,
he was working on a project to dry fresh
cut wood fast! With his planned system,
he said, we wouldn’t have to turn green
wood and guess at what its final shape
might be. Being a writer, I told him it
might make a good article. Since then,
we’ve crossed trails several times. Each
time we met, he hadn’t perfected his
dryer yet. He was still working on it.

Then “out of the blue” he called me.
His project had finally been worked out.
His system can dry a kiln full of wet
(newly cut) fruit wood to 6 percent moisture
content in three to seven days depending
upon the thickness of the timber,
about the best I’ve heard of is almost a
month. This new system uses a low temperature
(100 to 150 degrees) and a
vacuum pump. Gilbert says, he isn’t going
to mass produce these units but will
make one up for someone on special order.
If interested, you can contact him
at: Gilbert Brown, Route 3, Box 336-B,
Omak, WA 98841. You can call him at:
509-826-4058. (Note: Gilbert wasn't in extremely
good health at the time I wrote this article
and he may no longer be able to produce a unit
on order.)

The unit that Gilbert has devised uses
a two-foot diameter steel tank that is 10
feet long as his vacuum chamber. One
end of the tank has a door that can be
opened for loading and unloading the
chamber. The door is equipped with a
small Plexiglass window so that the wood
can be viewed during the drying operation.
A light bulb is also installed in the
tank to assist in this.

The vacuum tank is mounted inside
a wooden box with an air chamber between
the tank and the sides of the box.
The walls of the box are one to two feet
thick with sawdust used as a filler and
for insulation. A tube type thermometer
is used to measure temperature within
the vacuum chamber. Finally, a vacuum
is pulled; a reading of 15 on the gauge is
adequate.

When loaded with wet wood that has
been brought up to temperature, beads
of water will appear on the ends of the
boards about six minutes after the
vacuum is established. Apparently, the
moisture is removed from the wood along
the channels that the moisture moved in
when the tree was alive. You don’t get
to view what’s going on for very long before
the window is fully fogged with moisture.

Gilbert has been making lumber from
fruit wood stumps. He says, a cherry
wood stump that is three feet long and
about 16 inches in diameter weighs about
300 pounds. Such a stump will produce
about three gallons of water in three days.
This water collects in the bottom of the
tank. He has installed a drain valve in
the bottom of the vacuum tank so that
the water can be removed and saved in
another smaller tank without losing the
vacuum.

This dryer was developed to quickly
dry fruit wood from the orchards around
Omak, Washington to produce cabinet
grade lumber at the lowest possible cost.
Gilbert uses the stumps that regular mills
leave behind. Here, much of the figure
in the tree exists so that really fine wood
can be obtained from a part of the tree
that would otherwise be burned. Of
course, this process doesn’t yield long
pieces of timber, but most cabinets don’t
need very long pieces. Gilbert also makes
up fancy flooring from this wood by laminating
the pieces to form larger boards
with an appropriate pattern.

Fruit woods will twist a good deal
during this fast drying process, unless they
are clamped down while drying. Other
woods seem to be alright, he says. Gilbert
described a typical load of fruit wood
to be boards that are about one inch thick,
either trimmed up or with the bark left
on. The boards are stacked on a 1/4 inch
metal plate. They are then clamped down
to the plate to hold them in position while
they dry. Once dry, Gilbert says, the
boards are OK. Wax sealer on the ends
of the boards will help to keep them from
cracking.

Currently, I have quite a bit of wood
on the shelf that was cut six months to
two years ago that still isn’t ready to turn.
I’m waiting for it to air dry at about one
inch per year. I can see how a small kiln
of this type that would hold a few green
wood bowl blanks or several small pieces
for other turning projects would be very
useful. I turn small pieces such as wine
bottle stoppers and spinner tops. These
must be dry before you turn them. A
small kiln with a vacuum tank about the
size of a five gallon bucket, which
wouldn’t take up too much space in my
shop, would work well for me. I could
dry more wood with such a small unit
than I have time to turn.

Editor’s Note: This article was
written for Fine Woodworking in cooperation
with Gilbert. After almost a
year, Fine Woodworking returned the
article, saying that the “experts” they
had contacted said the system wouldn’t
work. I don’t make any claims about
Gilberts system, but I believe he is honest
and that he has worked out a system
that will dry wood quickly. I have
held off publishing this in More
Woodturning in hopes that I could find
a publication with larger circulation
to spread the word about this system.
Anyone wishing to investigate this further
should contact Gilbert Brown directly
at the address given above. The
way he talked, he would be willing to
make up systems of virtually any size.

Fred Holder
http://www.fholder.com


--
NewsGuy.Com 30Gb $9.95 Carry Forward and On Demand Bandwidth

Fred:

Interesting.... but several thoughts come to mind...

The heat in the box around the vacuum chamber may heat the walls of the
chamber. Heat can move via convection or conduction. The problem is,
that with no (or very little) air in the chamber, convection cannot take
place. So, conduction is the only way of transferring the heat to the
wood. Since the wood is minimally in contact with the chamber, I doubt
that the heat can have any effect at all.

Vacuum kilns are a proven technology. But, they rely on heating
blankets in contact with each and every piece of wood. Also, if the
wood is thick, the surface is going to dry much faster than the core
leading to all sorts of problems.

When the pressure is lowered, the boiling point of water is lowered --
that 212F is at a standard pressure only. Vacuum kilns work by raising
the temperature and lowering the pressure so as to change the water in
the wood to vapor which passes through the cell walls more easily than
water.

I tend to think that Fine Woodworking is right.

Bill

Fred Holder wrote:
The various discussions on ways of drying wood prompted me to post this message.

The following article was published in the March 1998 issue of More Woodturning.
I authored the article with technical help from Gilbert Brown of Omak,
Washington. Gilbert had done considerable experimenting with his process and was
trying to market the system with little success. I wrote the article and
submitted it to Fine Woodworking. They kept it for a year and then returned it
saying that their experts said it would not work. I leave it to the reader to
determine whether this might be useful.

I first met Gilbert Brown at the 1993
“Art in the Park” craft fair at Omak,
Washington. Several of the bowls on my
table were turned from wet wood and
had warped appropriately. Gilbert said,
he was working on a project to dry fresh
cut wood fast! With his planned system,
he said, we wouldn’t have to turn green
wood and guess at what its final shape
might be. Being a writer, I told him it
might make a good article. Since then,
we’ve crossed trails several times. Each
time we met, he hadn’t perfected his
dryer yet. He was still working on it.

Then “out of the blue” he called me.
His project had finally been worked out.
His system can dry a kiln full of wet
(newly cut) fruit wood to 6 percent moisture
content in three to seven days depending
upon the thickness of the timber,
about the best I’ve heard of is almost a
month. This new system uses a low temperature
(100 to 150 degrees) and a
vacuum pump. Gilbert says, he isn’t going
to mass produce these units but will
make one up for someone on special order.
If interested, you can contact him
at: Gilbert Brown, Route 3, Box 336-B,
Omak, WA 98841. You can call him at:
509-826-4058. (Note: Gilbert wasn't in extremely
good health at the time I wrote this article
and he may no longer be able to produce a unit
on order.)

The unit that Gilbert has devised uses
a two-foot diameter steel tank that is 10
feet long as his vacuum chamber. One
end of the tank has a door that can be
opened for loading and unloading the
chamber. The door is equipped with a
small Plexiglass window so that the wood
can be viewed during the drying operation.
A light bulb is also installed in the
tank to assist in this.

The vacuum tank is mounted inside
a wooden box with an air chamber between
the tank and the sides of the box.
The walls of the box are one to two feet
thick with sawdust used as a filler and
for insulation. A tube type thermometer
is used to measure temperature within
the vacuum chamber. Finally, a vacuum
is pulled; a reading of 15 on the gauge is
adequate.

When loaded with wet wood that has
been brought up to temperature, beads
of water will appear on the ends of the
boards about six minutes after the
vacuum is established. Apparently, the
moisture is removed from the wood along
the channels that the moisture moved in
when the tree was alive. You don’t get
to view what’s going on for very long before
the window is fully fogged with moisture.

Gilbert has been making lumber from
fruit wood stumps. He says, a cherry
wood stump that is three feet long and
about 16 inches in diameter weighs about
300 pounds. Such a stump will produce
about three gallons of water in three days.
This water collects in the bottom of the
tank. He has installed a drain valve in
the bottom of the vacuum tank so that
the water can be removed and saved in
another smaller tank without losing the
vacuum.

This dryer was developed to quickly
dry fruit wood from the orchards around
Omak, Washington to produce cabinet
grade lumber at the lowest possible cost.
Gilbert uses the stumps that regular mills
leave behind. Here, much of the figure
in the tree exists so that really fine wood
can be obtained from a part of the tree
that would otherwise be burned. Of
course, this process doesn’t yield long
pieces of timber, but most cabinets don’t
need very long pieces. Gilbert also makes
up fancy flooring from this wood by laminating
the pieces to form larger boards
with an appropriate pattern.

Fruit woods will twist a good deal
during this fast drying process, unless they
are clamped down while drying. Other
woods seem to be alright, he says. Gilbert
described a typical load of fruit wood
to be boards that are about one inch thick,
either trimmed up or with the bark left
on. The boards are stacked on a 1/4 inch
metal plate. They are then clamped down
to the plate to hold them in position while
they dry. Once dry, Gilbert says, the
boards are OK. Wax sealer on the ends
of the boards will help to keep them from
cracking.

Currently, I have quite a bit of wood
on the shelf that was cut six months to
two years ago that still isn’t ready to turn.
I’m waiting for it to air dry at about one
inch per year. I can see how a small kiln
of this type that would hold a few green
wood bowl blanks or several small pieces
for other turning projects would be very
useful. I turn small pieces such as wine
bottle stoppers and spinner tops. These
must be dry before you turn them. A
small kiln with a vacuum tank about the
size of a five gallon bucket, which
wouldn’t take up too much space in my
shop, would work well for me. I could
dry more wood with such a small unit
than I have time to turn.

Editor’s Note: This article was
written for Fine Woodworking in cooperation
with Gilbert. After almost a
year, Fine Woodworking returned the
article, saying that the “experts” they
had contacted said the system wouldn’t
work. I don’t make any claims about
Gilberts system, but I believe he is honest
and that he has worked out a system
that will dry wood quickly. I have
held off publishing this in More
Woodturning in hopes that I could find
a publication with larger circulation
to spread the word about this system.
Anyone wishing to investigate this further
should contact Gilbert Brown directly
at the address given above. The
way he talked, he would be willing to
make up systems of virtually any size.

Fred Holder
http://www.fholder.com

What troubles me is that the window fogs up, and water collects on the
bottom of the chamber. If the vacuum is causing the water to evaporate, why
doesn't it evaporate from the areas outside the wood? If the system is
working, it must be some other mechanism than vacuum drying.

In article ,
"Leo Lichtman" wrote:

What troubles me is that the window fogs up, and water collects on the
bottom of the chamber. If the vacuum is causing the water to evaporate, why
doesn't it evaporate from the areas outside the wood? If the system is
working, it must be some other mechanism than vacuum drying.

Certainly operating it at a minimal vacuum ("15", probably 15 inches of
mercury, or about 1/2 atmosphere - a very low vacuum indeed) offers some
room for doubt about its method of operation. The standing water (there
is mention of removing it) would indicate that the water in the wood is
not boiling off, so the only means I can guess at for the expulsion of
this water from the wood would be small gas bubbles in the pores driving
(free) water out the pores. That would leave the bound water behind.
Fogging is pretty much a given, as the thing will be operating at 100%
humidity for whatever pressure and temperature it's running at. On the
other hand, at 1/2 an atmosphere, heat (mentioned in another reply) will
convect quite well, there being very little vacuum insulation effect at
that high a pressure.

With a better vacuum heat is not really needed, as water will boil at
and below room temperature, and if the wood self-cools (due to boiling
of water in it) to below freezing, water will sublime out of the ice -
freeze drying (intentional freeze drying starts with freezing the object
to be dried). I believe that some of the commercial kilns (or at least a
research project test kiln of commercial size I've read about) have a
more effective means (than contact blankets) of providing heat in vacuum
to improve cycle times, however - microwaves.

Most of the degrade issues of any drying process remain on the table
with vacuum drying, as I see it; this may be one reason for choosing
such a low level of vacuum, as extreme speed of drying can aggravate
degrade. Also, heat can improve some degrade issues by allowing the wood
to bend plastically - so if it's restrained flat and heated sufficiently
(not very applicable to bowls, I'm afraid) it can relieve stresses that
might tend to twist or cup it, and set flat. Also, sufficient heat to
kill bugs is a good thing.

--
Cats, coffee, chocolate...vices to live by

"Bill Rubenstein" wrote in message
. com...
Fred:

Interesting.... but several thoughts come to mind...

The heat in the box around the vacuum chamber may heat the walls of the
chamber. Heat can move via convection or conduction. The problem is,
that with no (or very little) air in the chamber, convection cannot take
place. So, conduction is the only way of transferring the heat to the
wood. Since the wood is minimally in contact with the chamber, I doubt
that the heat can have any effect at all.

Vacuum kilns are a proven technology. But, they rely on heating blankets
in contact with each and every piece of wood. Also, if the wood is thick,
the surface is going to dry much faster than the core leading to all sorts
of problems.

When the pressure is lowered, the boiling point of water is lowered --
that 212F is at a standard pressure only. Vacuum kilns work by raising
the temperature and lowering the pressure so as to change the water in the
wood to vapor which passes through the cell walls more easily than water.

I tend to think that Fine Woodworking is right.

Well, I'm going with the cheeseheads at FPL. It's relative humidity and
Raoult's law all the way. Raising the temperature of the air in the chamber
effectively lowers the relative humidity, pulling a vacuum allows escape of
water to air with application of less energy in the form of heat.
Combination is a quick way to get rid of the unbound water, that's for sure.

For the individual who said that cold air is a low humidity environment -
half correct. Low _absolute_ humidity, high _relative_ humidity. With
Raoult's law, the vapor pressure over the wood will dictate how much water
can leave and at what rate. At saturation - the dewpoint - none can leave.
That's why you have to continue to remove the humid air whether in a
standard kiln, vacuum kiln, or slowly through a barrier like a paper bag,
anchorseal or news paper.

Fred, Could FW have returned the article because it had already been published,
instead of for technical reasons? Dan

"Fred Holder" wrote in message
...
The various discussions on ways of drying wood prompted me to post this
message.

The following article was published in the March 1998 issue of More
Woodturning.
I authored the article with technical help from Gilbert Brown of Omak,
Washington. Gilbert had done considerable experimenting with his process and
was
trying to market the system with little success. I wrote the article and
submitted it to Fine Woodworking. They kept it for a year and then returned it
saying that their experts said it would not work. I leave it to the reader to
determine whether this might be useful.

I first met Gilbert Brown at the 1993
“Art in the Park” craft fair at Omak,
Washington. Several of the bowls on my
table were turned from wet wood and
had warped appropriately. Gilbert said,
he was working on a project to dry fresh
cut wood fast! With his planned system,
he said, we wouldn’t have to turn green
wood and guess at what its final shape
might be. Being a writer, I told him it
might make a good article. Since then,
we’ve crossed trails several times. Each
time we met, he hadn’t perfected his
dryer yet. He was still working on it.

Then “out of the blue” he called me.
His project had finally been worked out.
His system can dry a kiln full of wet
(newly cut) fruit wood to 6 percent moisture
content in three to seven days depending
upon the thickness of the timber,
about the best I’ve heard of is almost a
month. This new system uses a low temperature
(100 to 150 degrees) and a
vacuum pump. Gilbert says, he isn’t going
to mass produce these units but will
make one up for someone on special order.
If interested, you can contact him
at: Gilbert Brown, Route 3, Box 336-B,
Omak, WA 98841. You can call him at:
509-826-4058. (Note: Gilbert wasn't in extremely
good health at the time I wrote this article
and he may no longer be able to produce a unit
on order.)

The unit that Gilbert has devised uses
a two-foot diameter steel tank that is 10
feet long as his vacuum chamber. One
end of the tank has a door that can be
opened for loading and unloading the
chamber. The door is equipped with a
small Plexiglass window so that the wood
can be viewed during the drying operation.
A light bulb is also installed in the
tank to assist in this.

The vacuum tank is mounted inside
a wooden box with an air chamber between
the tank and the sides of the box.
The walls of the box are one to two feet
thick with sawdust used as a filler and
for insulation. A tube type thermometer
is used to measure temperature within
the vacuum chamber. Finally, a vacuum
is pulled; a reading of 15 on the gauge is
adequate.

When loaded with wet wood that has
been brought up to temperature, beads
of water will appear on the ends of the
boards about six minutes after the
vacuum is established. Apparently, the
moisture is removed from the wood along
the channels that the moisture moved in
when the tree was alive. You don’t get
to view what’s going on for very long before
the window is fully fogged with moisture.

Gilbert has been making lumber from
fruit wood stumps. He says, a cherry
wood stump that is three feet long and
about 16 inches in diameter weighs about
300 pounds. Such a stump will produce
about three gallons of water in three days.
This water collects in the bottom of the
tank. He has installed a drain valve in
the bottom of the vacuum tank so that
the water can be removed and saved in
another smaller tank without losing the
vacuum.

This dryer was developed to quickly
dry fruit wood from the orchards around
Omak, Washington to produce cabinet
grade lumber at the lowest possible cost.
Gilbert uses the stumps that regular mills
leave behind. Here, much of the figure
in the tree exists so that really fine wood
can be obtained from a part of the tree
that would otherwise be burned. Of
course, this process doesn’t yield long
pieces of timber, but most cabinets don’t
need very long pieces. Gilbert also makes
up fancy flooring from this wood by laminating
the pieces to form larger boards
with an appropriate pattern.

Fruit woods will twist a good deal
during this fast drying process, unless they
are clamped down while drying. Other
woods seem to be alright, he says. Gilbert
described a typical load of fruit wood
to be boards that are about one inch thick,
either trimmed up or with the bark left
on. The boards are stacked on a 1/4 inch
metal plate. They are then clamped down
to the plate to hold them in position while
they dry. Once dry, Gilbert says, the
boards are OK. Wax sealer on the ends
of the boards will help to keep them from
cracking.

Currently, I have quite a bit of wood
on the shelf that was cut six months to
two years ago that still isn’t ready to turn.
I’m waiting for it to air dry at about one
inch per year. I can see how a small kiln
of this type that would hold a few green
wood bowl blanks or several small pieces
for other turning projects would be very
useful. I turn small pieces such as wine
bottle stoppers and spinner tops. These
must be dry before you turn them. A
small kiln with a vacuum tank about the
size of a five gallon bucket, which
wouldn’t take up too much space in my
shop, would work well for me. I could
dry more wood with such a small unit
than I have time to turn.

Editor’s Note: This article was
written for Fine Woodworking in cooperation
with Gilbert. After almost a
year, Fine Woodworking returned the
article, saying that the “experts” they
had contacted said the system wouldn’t
work. I don’t make any claims about
Gilberts system, but I believe he is honest
and that he has worked out a system
that will dry wood quickly. I have
held off publishing this in More
Woodturning in hopes that I could find
a publication with larger circulation
to spread the word about this system.
Anyone wishing to investigate this further
should contact Gilbert Brown directly
at the address given above. The
way he talked, he would be willing to
make up systems of virtually any size.

Fred Holder
http://www.fholder.com


--
NewsGuy.Com 30Gb $9.95 Carry Forward and On Demand Bandwidth

Dan, I think that they would have said so had the information already been
published. I believe that the experts that they contacted, who ever they may
have been, simply felt that the process would not work. If I had had room in my
shop for a small version of his kiln, I would have had him make one for me to
try myself.

If I understood him correctly. His kiln was sealed so that he did not have to
run a vacuum pump continuously. He simply pulled 15 inches of vacuum in the
chamber and applied a small amount of heat. The pressure in the wood then pushed
out the water and it settled into the bottom of his tank where he could drain
off the water. He insulated the tank to keep from losing his heat so that he
could run this system any time of the year.

Since his system was somewhat radical in relation to the current thinking,
everyone, who was considered an expert, felt that it could not possibly work.

I think it is a bit like Dave Smith's alcohol drying method. It is claimed by
many that this could not possibly work. I happen to know that it does work
through our own experiments with it on woods like madrone, which was dry enough
to final turn in seven days after overnight soaking in alcohol.

Gilbert Brown did not have enough money to really push his system; hence, it was
never really given a fair trial I suspect.

Fred Holder
http://www.fholder.com

In article j_N1g.692726$084.333379@attbi_s22, Dan Bollinger says...

Fred, Could FW have returned the article because it had already been published,
instead of for technical reasons? Dan

"Fred Holder" wrote in message
...
The various discussions on ways of drying wood prompted me to post this
message.

The following article was published in the March 1998 issue of More
Woodturning.
I authored the article with technical help from Gilbert Brown of Omak,
Washington. Gilbert had done considerable experimenting with his process and
was
trying to market the system with little success. I wrote the article and
submitted it to Fine Woodworking. They kept it for a year and then returned it
saying that their experts said it would not work. I leave it to the reader to
determine whether this might be useful.

I first met Gilbert Brown at the 1993
“Art in the Park” craft fair at Omak,
Washington. Several of the bowls on my
table were turned from wet wood and
had warped appropriately. Gilbert said,
he was working on a project to dry fresh
cut wood fast! With his planned system,
he said, we wouldn’t have to turn green
wood and guess at what its final shape
might be. Being a writer, I told him it
might make a good article. Since then,
we’ve crossed trails several times. Each
time we met, he hadn’t perfected his
dryer yet. He was still working on it.

Then “out of the blue” he called me.
His project had finally been worked out.
His system can dry a kiln full of wet
(newly cut) fruit wood to 6 percent moisture
content in three to seven days depending
upon the thickness of the timber,
about the best I’ve heard of is almost a
month. This new system uses a low temperature
(100 to 150 degrees) and a
vacuum pump. Gilbert says, he isn’t going
to mass produce these units but will
make one up for someone on special order.
If interested, you can contact him
at: Gilbert Brown, Route 3, Box 336-B,
Omak, WA 98841. You can call him at:
509-826-4058. (Note: Gilbert wasn't in extremely
good health at the time I wrote this article
and he may no longer be able to produce a unit
on order.)

The unit that Gilbert has devised uses
a two-foot diameter steel tank that is 10
feet long as his vacuum chamber. One
end of the tank has a door that can be
opened for loading and unloading the
chamber. The door is equipped with a
small Plexiglass window so that the wood
can be viewed during the drying operation.
A light bulb is also installed in the
tank to assist in this.

The vacuum tank is mounted inside
a wooden box with an air chamber between
the tank and the sides of the box.
The walls of the box are one to two feet
thick with sawdust used as a filler and
for insulation. A tube type thermometer
is used to measure temperature within
the vacuum chamber. Finally, a vacuum
is pulled; a reading of 15 on the gauge is
adequate.

When loaded with wet wood that has
been brought up to temperature, beads
of water will appear on the ends of the
boards about six minutes after the
vacuum is established. Apparently, the
moisture is removed from the wood along
the channels that the moisture moved in
when the tree was alive. You don’t get
to view what’s going on for very long before
the window is fully fogged with moisture.

Gilbert has been making lumber from
fruit wood stumps. He says, a cherry
wood stump that is three feet long and
about 16 inches in diameter weighs about
300 pounds. Such a stump will produce
about three gallons of water in three days.
This water collects in the bottom of the
tank. He has installed a drain valve in
the bottom of the vacuum tank so that
the water can be removed and saved in
another smaller tank without losing the
vacuum.

This dryer was developed to quickly
dry fruit wood from the orchards around
Omak, Washington to produce cabinet
grade lumber at the lowest possible cost.
Gilbert uses the stumps that regular mills
leave behind. Here, much of the figure
in the tree exists so that really fine wood
can be obtained from a part of the tree
that would otherwise be burned. Of
course, this process doesn’t yield long
pieces of timber, but most cabinets don’t
need very long pieces. Gilbert also makes
up fancy flooring from this wood by laminating
the pieces to form larger boards
with an appropriate pattern.

Fruit woods will twist a good deal
during this fast drying process, unless they
are clamped down while drying. Other
woods seem to be alright, he says. Gilbert
described a typical load of fruit wood
to be boards that are about one inch thick,
either trimmed up or with the bark left
on. The boards are stacked on a 1/4 inch
metal plate. They are then clamped down
to the plate to hold them in position while
they dry. Once dry, Gilbert says, the
boards are OK. Wax sealer on the ends
of the boards will help to keep them from
cracking.

Currently, I have quite a bit of wood
on the shelf that was cut six months to
two years ago that still isn’t ready to turn.
I’m waiting for it to air dry at about one
inch per year. I can see how a small kiln
of this type that would hold a few green
wood bowl blanks or several small pieces
for other turning projects would be very
useful. I turn small pieces such as wine
bottle stoppers and spinner tops. These
must be dry before you turn them. A
small kiln with a vacuum tank about the
size of a five gallon bucket, which
wouldn’t take up too much space in my
shop, would work well for me. I could
dry more wood with such a small unit
than I have time to turn.

Editor’s Note: This article was
written for Fine Woodworking in cooperation
with Gilbert. After almost a
year, Fine Woodworking returned the
article, saying that the “experts” they
had contacted said the system wouldn’t
work. I don’t make any claims about
Gilberts system, but I believe he is honest
and that he has worked out a system
that will dry wood quickly. I have
held off publishing this in More
Woodturning in hopes that I could find
a publication with larger circulation
to spread the word about this system.
Anyone wishing to investigate this further
should contact Gilbert Brown directly
at the address given above. The
way he talked, he would be willing to
make up systems of virtually any size.

Fred Holder
http://www.fholder.com


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"Fred Holder" wrote: (clip) If I understood him correctly. His kiln was
sealed so that he did not have to run a vacuum pump continuously. He simply
pulled 15 inches of vacuum in the chamber and applied a small amount of
heat. (clip)
^^^^^^^^^^^^^^^^^
If you want to vacuum dry something effectively, you must run the pump
continuously. Otherwise, the partial pressure of the moisture in the
chamber rises to the equilibrium vapor pressure for that temperature, and no
further water is removed. Your supposition that the pressure in the wood
pushes out the liquid water doesn't sit well with me. Water is essentially
incompressible. Pulling a vacuum on the outside of the wood would be
rewarded with an infinitesimal flow of liquid, and then the internal
pressure would drop to match the chamber pressure.

"Fred Holder" wrote: (clip) If I understood him correctly. His kiln was
sealed so that he did not have to run a vacuum pump continuously. He simply
pulled 15 inches of vacuum in the chamber and applied a small amount of heat.
(clip)
^^^^^^^^^^^^^^^^^
If you want to vacuum dry something effectively, you must run the pump
continuously. Otherwise, the partial pressure of the moisture in the chamber
rises to the equilibrium vapor pressure for that temperature, and no further
water is removed. Your supposition that the pressure in the wood pushes out
the liquid water doesn't sit well with me. Water is essentially
incompressible. Pulling a vacuum on the outside of the wood would be rewarded
with an infinitesimal flow of liquid, and then the internal pressure would
drop to match the chamber pressure.

I think you are both right. It is possible that internal gases expand and
physically push the water out. I'm sure that a good portion of water would be
extracted, but eventually, it will reach equilibrium. As pressure decreases (as
in pulling a vacuum) water evaporates and may even boil. As it does so heat is
removed and the remaining water can freeze. I suspect this may be the reason
this and other vacuum dryers add heat. Even freeze dryers have heated shelves.
Too see this effect, find a phase diagram that is graphed below one atomosphere.

Water boils at about 27" Hg at room temperature.

I'm doing a little test right now; put a green sapling sample in a vacuum tank
at 15".

Dan

My sense is whatever he did is not exactly explained by the article,
since you guys don't seem to understand the thermodynamics of what's
happening, so it probably reads like an amateur science experiment
without adequate explanation, and the way it was described it actually
wouldn't work, and that's why it was rejected. Obviously I haven't read
it, so I don't know. There may also be temperature gradients in the
thing that you aren't aware of and THAT's the only thing that makes it
work.

For example, the fog on window makes sense because the window is likely
a path for heat to escape, and being a lower temperature, it would
condense drops, esp when the wood's giving off a lot of water.

I've dried metal things in vacuum ovens a lot in the past...it's common
practice in aerospace, and fog happens. We usu. keep the pump on, but
sometimes pressure cycling can remove moisture a bit faster, (and maybe
transfer heat convectively to the inner parts faster?). What kind of
heat supply? Sun lamp? Heater blankets or tape?

I'd think a cold trap for condensing moisture between the oven and the
pump would make sense, cycle regularly to remove water from it, and
maybe that's sort of what you've got and just don't know it.

Leo:

Well, this discussion has effectively separated the men from the boys
when it comes to a science and engineering background. My degrees are
in music (from a conservatory, yet) so I'm one of the boys.

My experience with a vacuum kiln was some years ago (late 90s) and it
was built and sold by Woodmizer. It appears as if they are no longer
selling it and that, in my opinion, is no loss. We tried to use it for
drying exotics and blew up thousands of dollars of wood before it was
returned to Woodmizer.

This kiln DID use electric blankets between the layers and drying was
most uneven -- wet boards next to dry ones. I have heard of kilns which
use microwave heating as stated in a prior message in this thread.

The Woodmizer did not run the pump all the time. They had a vacuum
gauge and a microcomputer which cycled the pump and maintained the
desired vacuum. To put their computer technology in perspective, as I
remember, the microcomputer was a 6502 for those who are old enough to
remember that one -- I am.

They pumped the water out through the vacuum pump and we collected it in
a bucket.

Bill

Leo Lichtman wrote:
"Fred Holder" wrote: (clip) If I understood him correctly. His kiln was
sealed so that he did not have to run a vacuum pump continuously. He simply
pulled 15 inches of vacuum in the chamber and applied a small amount of
heat. (clip)
^^^^^^^^^^^^^^^^^
If you want to vacuum dry something effectively, you must run the pump
continuously. Otherwise, the partial pressure of the moisture in the
chamber rises to the equilibrium vapor pressure for that temperature, and no
further water is removed. Your supposition that the pressure in the wood
pushes out the liquid water doesn't sit well with me. Water is essentially
incompressible. Pulling a vacuum on the outside of the wood would be
rewarded with an infinitesimal flow of liquid, and then the internal
pressure would drop to match the chamber pressure.

"Bill Rubenstein" wrote in message
om...
Leo:

Well, this discussion has effectively separated the men from the boys when
it comes to a science and engineering background. My degrees are in music
(from a conservatory, yet) so I'm one of the boys.


Well, you can always study on this very screen. I keep posting it over
and over, but the place to start is http://www.fpl.fs.fed.us/ where you may
download the Wood Handbook and read how wood really dries. Thousands of
years of experience, millions of dollars of documented research available at
the click of a mouse. You may even elect to go directly to the drying
literature through the search function.

Or, you may chose to believe rather than explore. Lot of individual comfort
in faith, where snake oil and spirit messages become panaceas and
prophecies. It's an uncomfortable thing to study, because in the process
you discover that you don't know or understand some things well enough,
which you remedy with further study, only to discover there are other things
you don't know ....

Beware the halo effect.

Bill,

Well, this discussion has effectively separated the men from the boys when
it comes to a science and engineering background.
Agreed but practical experience like Fred's with alcohol seems hard to
ignore.

blew up thousands of dollars of wood before it was returned to Woodmizer.
Do you mean literally ruptured? Man, would that be a bummer.
At a high vacuum I could see that happening.

Earlier comment about 27" at room tempeature fits my experience with air
conditioning evacuation at closer to 29". Moisture/vapor exhausts through
the pump. Shutting off the pump and watching for a drop is a leak test
procedure. System's sealing quality probably a lot higher than a large
homemade system.

Well, you can always study on this very screen. I keep posting it over
and over, but the place to start is http://www.fpl.fs.fed.us/ where you may
download the Wood Handbook and read how wood really dries. Thousands of
years of experience, millions of dollars of documented research available at
the click of a mouse. You may even elect to go directly to the drying
literature through the search function.

Great resource. I made my solar kiln using plans on their website and
it works very well.

Tom:

When I used the term 'blow up' I didn't mean literally. We ended up
with unsaleable wood due to water pockets, uneven drying, checking... A
real mess.

Bill

Tom Nie wrote:
Bill,


Well, this discussion has effectively separated the men from the boys when
it comes to a science and engineering background.

Agreed but practical experience like Fred's with alcohol seems hard to
ignore.


blew up thousands of dollars of wood before it was returned to Woodmizer.

Do you mean literally ruptured? Man, would that be a bummer.
At a high vacuum I could see that happening.

Earlier comment about 27" at room tempeature fits my experience with air
conditioning evacuation at closer to 29". Moisture/vapor exhausts through
the pump. Shutting off the pump and watching for a drop is a leak test
procedure. System's sealing quality probably a lot higher than a large
homemade system.

OK, so I stick my blank in the Hoover, put the Hoover in the Frigidaire,
put the Frigidaire in the oven, set the oven on a scale to see when
weight loss stops. What temp do I set the oven at?

Steve A wrote:

OK, so I stick my blank in the Hoover, put the Hoover in the Frigidaire,
put the Frigidaire in the oven, set the oven on a scale to see when
weight loss stops. What temp do I set the oven at?


350F