home made drying kiln
tracey+
I am after some help. Can anyone tell me how to build a small kiln around
1200millimetre square. Heating and ventilation details would be greatly
appreciated. Alternatively, if you could provide a link of a relavant site
to visit with this information.
Thanks
Ray R
AHilton
... Use some light bulbs (2 - 100 watt ones should be fine even in winter
conditions) and a small fan (junked computer fans or over the kitchen stove
hood fan or whatever you can find) inside a simple box or even a plastic
containter of some kind but it needs to be waterproof or it won't last long.
Simply having an opening to let air in and out isn't enough. You need actual
air *movement* at certain times.
Have a separate switch for the lights (heat source) and for the fan
(ventilation) because you'll be controlling those factors individually. You
need to have some kind of thermometer (temperature guage) as well as a
hygrometer (humidity guage) inside the kiln that you can read from the
outside without opening the kiln if possible. This will be checked very
often in such a small kiln to regulate the environment inside. A simple
piece of glass in the side of the kiln to read these things would work but
might be tough to read sometimes with the condensation build up. Don't just
lay your wood on the bottom. Raise them on blocks of some sort to let air
circulate around them.
Do a search on the internet for "kiln drying schedule" and you'll get some
information on that aspect. The most important of all. In the most extreme
general sense, here are the basics of a drying schedule which is broken down
into about equal 1/3rds of time...
1) High humidity. Lots of heat (no more than 140F) with no air movement and
no ventilation
2) Medium humidity. Some ventilation (turn the fans on about half a day).
Heat around 100F. Drawing the moisture out *gently*.
3) Low humidity. Plenty of ventilation and airflow. Heat a little higher
(120F) to draw the little moisture out that's still in there.
You'll have to play around with the drying schedule with each different
specie of wood and many other factors. Just go slow and easy at first until
you get the hang of it. It's VERY easy to go too fast and crack the wood in
a kiln.
Yes, I have my own small kiln (about 15 cubic feet) and love it.
- Andrew
"tracey+" <trace...@hotmail.com> wrote in message
news:bcbqs2$pcj$1...@yeppa.connect.com.au...
George
And many, many more publications dealing with wood.
http://www.fpl.fs.fed.us/TMU/publications.htm
"AHilton" <ahil...@hotmail.com> wrote in message
news:A48B4DD9627BD2118B1...@useserver.usexpr...
SNIP
> Do a search on the internet for "kiln drying schedule" and you'll get some
> information on that aspect. The most important of all. In the most
extreme
> general sense, here are the basics of a drying schedule which is broken
down
> into about equal 1/3rds of time...
>
SNIP
Chuck
wrote:
Andy,
>3) Low humidity. Plenty of ventilation and airflow. Heat a little higher
>(120F) to draw the little moisture out that's still in there.
As I understand it, this is the least critical stage, as far as timing
goes. As with drying a turned piece in the microwave, you can only
get the wood so dry, after which it will just reabsorb moisture until
it is at ambient humidity. Of course, with a kiln, it is a much
gentler process, since you are working with cooler temperatures and a
longer period of time.
Question, though. If 100 degrees is enough to draw out moisture at
medium humidity, why wouldn't it do it just as well at low humidity?
--
Chuck *#:^)
chaz3913(AT)yahoo(DOT)com
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George
Key is to keep the gradient between the interior and exterior from becoming
too great. Not much of a problem when the interior is warmer, pushing
moisture toward the surface, as in microwave.
"Chuck" <chaz391...@yahoo.com> wrote in message
news:3eea19bc...@news.capital.net...
> On Fri, 13 Jun 2003 07:32:32 -0500, "AHilton" <ahil...@hotmail.com>
AHilton
First, let me say that I'm relatively new to kiln drying having only built
my first kiln about 7 years ago. I don't have the decades of kiln drying
experience (especially the BIG commercial kiln dryers) of many folks that
might be monitoring this group. I can only go on the non-professional kiln
drying experience I have with 3 large and 2 (so far) small kilns I've made
over the years and the extensive research I've done especially while
designing my Micro-Kiln (not an available product, btw).
Hmmm I would agree that this last stage (of the example 3-stage scenario I
gave) would be the least
critical, yes, with this caveat.... it IS critical to determine *when* this
stage starts. Do realize that these stages aren't swift changeovers. They
are gradual transitions. The ending of this stage is easy to determine.
When you reach EMC, you're there. <g> It's tough to get into specifics
because all of these stages (and mini-stages) overlap or change with each
specie of wood or even just depending on the sticks of wood you have in
there. Once I get into the later stages of drying cycles, I'm far more
nervous about timing than the earlier stages but I think that might be just
the time invested at those later stages means more to me. At the start, I
figure if things get messed up then at least it didn't waste as much time.
<g> Still stinks that it messed up but not as much.
Your example with the microwave is quite different. It's using more of a
direct instead of an indirect method of moving moisture out of the wood. It
uses heat generation (microwave energy yada yada yada) to produce steam and
so on. Most "kilns" use more indirect methods that revolve around affecting
the surrounding environment (humidity primarily) and not the wood directly.
You certainly can get the wood much drier than the surounding environment
(the microwave interior) as long as the microwave is still on. After that,
you're right that the wood reabsorbs the moisture to try (that's a key word)
to get into EMC. The moisture doesn't penetrate as deeply back into the
wood as when it was forced out as steam though. This can cause major
problems. You can go too far and get it drier deep into the wood and wetter
in the shallow areas. A flip-flop.
In contrast, as you said, the kiln operation is gentler and slower. This
isn't saying that using other methods isn't valid or preferred but they are
just different. It's best to realize those differences and adjust your
methods, time, and expectations accordingly. I relate, in my own twisted
mind, the effects of kiln use as a "suck" method and that of a microwave,
for example, as a "blow" type of method. The kiln will "suck" the moisture
from the outer little part of the exposed wood. Drying schedules are
designed to allow that piece of wood to rest and have that lower moisture
content area in the wood to refill with the moisture from deeper in the
wood. The process is continuously repeated (phase 2 in my example), gently,
until the moisture deep in the wood is equal to the moisture shallow in the
wood. The moisture that is shallow in the wood at the end of the drying
schedule should, ideally, be the same as the outside (of the kiln) humidity
level.... or EMC to the outside environment. I know you already know this
but I'm trying to make myself clearer to those that don't. Probably poorly
but there you go. <g> So, in other words, you're affecting the environment
where the wood resides which, in turn, affects the wood indirectly. The
effect of heating the wood too is just incidental and can't be changed much.
You *could* really heat up that wood but then you've got other problems to
deal with. With a microwave, you're actually affecting the wood directly and
the environment is somewhat incidental and temporary.
Anyway, to answer your question if I undertand what you were asking, the
lower temperature (100F in my example ... and it IS JUST an example!) in
phase 2 is because 100F will only hold so much moisture and you're wanting
to go slow in this phase. The increase in temperature in the last phase
(120F in my example), seems to provide a little more "suck" of the moisture
and increase moisture absorption ability of the surrounding environment to
draw out those last bits of moisture from the shallow wood ... which, in
turn, "sucks" the moisture from the deep wood into the shallow wood better.
Since there is so little difference in moisture content between deep and
shallow wood, you need a gentle kick of increased temperature to get that
shallow wood moisture to move out into the environment. You *could* keep the
temperature the same between phase 2 and phase 3 but it takes longer. Do
NOT think that you'll just raise the temperature in phase 2 up to what you'd
normally use in phase 3 (120F in my example). You'll ruin wood that way.
Error on the side of too low of temperature (and too low of airflow too) in
phase 2 if anything. In phase 3 (assuming phase 2 was done properly)
there's less chance of having too great of a moisture gradient between deep
and shallow wood so you can raise that temperature to provide that extra
moisture "suck" and not be too afraid of ruining the wood. You don't need
that extra "kick" in phase 2 of a higher temperature because the moisture is
plentiful and just wanting to come out of it with any little bit of coaxing.
I hope I answered the question somewhere in that rambling. And this is JUST
discussing mainly the temperature factor! Care to go into airflow and
venting in detail too? <g> There are some detailed and well-written
articles on the web that discuss all of this much better than I can in my
ramblings. I encourage those interested in drying wood to seek them out
even if you're not interested in kilns. You'll get a better understanding of
the what's/why's of wood drying and relates to any kind of drying methods.
It's amazing ... at least to me. <g>
- Andrew
"Chuck" <chaz391...@yahoo.com> wrote in message
news:3eea19bc...@news.capital.net...
HerbIshii
could remove the refrigerant system. Drill a bunch of 1/4 inch vent holes
through the top and with a couple of holes in the bottom. If the box is a
combination freezer/refrig be sure to drill some holes in the partion that
separates the two compartments. Hook up and place a 40 or 60 watt light bulb
and a small fan in the bottom vegetable bin. The bulb heats the air and that
helps to draw moisture from the wood and the fan circulates the air out of the
"kiln". It works for me and a lot of others I know. Herb
OB O'Brien
completely different approach that has worked for me. I'm not really
sure of the mechanics, but it just works. I have a large home
gardener's type of dehydrator. I rough out a bowl, weigh it and put in
the dehydrator. Turn the thing on and set the temperature at the lowest
setting, 85 degrees. The next day I weigh the bowl again in the morning
and then again in the evening. This goes on for maybe three days. I
record the weights in grams and when I see there is less than 10 percent
change I take it out and let it come to EMC (?) It's now ready for
finishing. That's the way I found that works for me. Just thought I'd
let you all in on another method.
Regards
OB in Pensacola, Fl.
AHilton wrote: and OB snipped most all of it for brevity.
AHilton
of "kiln" drying ones in itself. I've tried several methods in my short
time as a woodturner and many more in my long time as a woodworker and there
are certainly differences between the two fields in drying wood most
effectively. That's why my newest kiln is geared more for the woodturning
end of it instead of general woodworking.
Do you keep track of the humidity in your dehydrator? What is that average
especially after the first 4 hours of putting just one freshly roughed out
bowl? I'm going to assume it's pretty low (since it's a DEhydrator <g>) but
your heat is also fairly low too. How "wet" of wood do you put in there?
Is it fresh cut damp wood or has it had time to dry a little? What woods? I
see you are in Florida. Gets kinda humid down there, eh? That's another
factor to contend with too. Have you tried taking 2 rough turned pieces
from side-by-side tree chunks and put one in your dehydrator and the other
just in a box for the same amount of time to compare the results?
There are many variables associated with drying wood and many are subtle but
yet powerful. I've tried using a commercial dehydrator before and it was
just too much "suck" (in keeping with the terminology I used before) and was
pretty harsh for me and my conditions (woods, greenness, environment, and so
on). It sure dried that wood fast though! <g> Not quite as harsh as the
microwave but close.
I don't use the kilns all the time and don't absolutely recommend kiln-type
drying to everyone. Afterall, I don't sell them. <g> Whatever works for
you then that's great. I hate when people think that I have to change what
I'm doing just because it doesn't work for them. <g> I often use the boil
and bag along with the (rare) microwave when it's appropriate. Any one
method couldn't possibly cover all the situations run into by us.
Thanks for the inclusion of your method OB,
- Andrew
"OB O'Brien" <ob-o...@mchsi.com> wrote in message
news:3EEDCA79...@mchsi.com...
cindy drozda
the air from the bottom to the top. I use 2 x 60W light bulbs in a chest
freezer (on end) to get a temp of about 90 degrees and never change it,
just put wood in and take it out. I've learned over experimentation time
how long different things take to dry. If I want a dry blank, I put a
square one in the drying box, and periodically cut off a corner and check
with a moisture meter (I get 4 tries).
A Q&D drying box can be made of "blue board" 2" construction foam glued
together with construction adhesive (PL400, Liquid nails, etc). Some
sticks of wood through the sides make "flow-through" shelves. 3/4" holes
in the sides at the top and bottom, and a couple of shop-light fixtures
with cheap 60W bulbs. The temp inside can be tuned by the number of holes
vs. the number and wattage of light bulbs.
Have fun!
-CD-
boulder co