Thread: home made kiln ??

every timber brye diferantly in a kiln just like air drying.

kilns are verry complicated devices. a pot belly in a container would just be like a hot box. you could not controll the heat well enough.

solar kilns are pretty mutch the same thing but take nothig to run. i have been meaning to build one for adges now. must get around to it one day.

Originally Posted by Mathuranatha

G,day there fellers , another few dumb questions from dumb ass mathuranatha .

Anyone made a home made kiln?
Could i just stick a pot belly in a shipping container with a couple of fans to circulate the air ?
Whats the best temperature to run them at approximately and how long for 1" boards and how long for 2"x4" and does hard wood take longer than hoop pine or camphor ?

Thanks ---mat

Do a search for kilns in the milling forum and you will plenty of scattered info.

For mountains of more specific and technical (it gets VERY technical) start at www.woodweb.com/KnowledgeBase/KBPP.html
A lot of this info is specific to North America where snowbound winters means things are very different to Australia.

To answer you specific questions I would say

Pot belly - they would be dangerous and not much good, and, are you gonna sit next to it all day and night and feed it? A better idea would be to put a slow combustion stove inside a dunny size room filled with rocks and then use a fan to draw warm air into the container from the rock filled room.

Unless you want the wood in a week a better type of kiln for Australia is a solar kiln. Look on wood web for ideas and examples

mathuranatha

where you are you have plenty of sun power so solar is the best.

There is however a halfway system between kiln and air dry which I have used for many years with good results.

you need to strip the timber out as for any drying process but make sure the stack is north /south. Using black plastic sheet make a tent over the stack with approx twice the volumne and at least 1m on both ends. Make one end of the tent 300mm higher or more than the other. Both ends MUST be open for air movement.

This will get sun all day generating the heat required. As one end is higher than the other this creates a convection and the hot air will be drawn out with cooler air replacing this. You will only get down to your ambient moisture level.

Its not as good as a full solar kiln but it is a lot faster than plain air drying. You can also control the airflow by the size of the exit end either letting more heat out or keeping it in.

You need to study up on kiln drying for different timbers. There are books and charts available from CSIRO and most likely the state forestry.

only one problem with that arthur.

teh tempriture has to mutch variation causing splitting.

a solar kiln has to be shut overnight to keep the temp up inside

i have done lots of reaserch and have a good desighn i just gotta get round to it.

if ya want it Mathuranatha i can send it to u.

Carl

Its not a replacement for a full kiln just an alternate to airdrying without the costs involved with kilns and running them.

The only drying system you can setup and walk away from is airdrying and even then you need to check on the pack now and again.

We have Rosegum Timbers across the valley from us and they manufacture some of the best solar kiln you can by with computer controls, etc,etc. At AUD$200K plus they are not cheap and still require checking two or three times a day while the drying process is happening. If you dont you will end up with dry but inferior timber. dry out too fast and some timbers will collapse.

The problem with the tent is there is no insulation to keep the heat in over night even if closing the ends. In damp areas this will allow the timber to rehydrate somewhat slowing the drying process down. We have done most of ours on the top section of a north facing slope and ended up with very good quality slabs and beams in well under half the normal drying times.

Although kiln drying is faster it is also more labour intensive but can be played with. Our next kiln is being built for hydrophobic timber production where extreme temperature, steam and various chemicals are all used to mess with the cell walls of the timber. Although reducing the strength by 30% the timber becomes water resistant and depending on the additional chemicals can also become somewhat fire resistant.

yer i now what u mean. it will speed up the drying. but at what cost. it will do more bamage than good.

Some of the first rosegum solar timber kilns used airconditioners on cool cycle to remove the humidity from within the kiln before going over to humidity sensors with air evaculation. So basically for a one off kiln you could use an insulated sea container, circulation fans with internal electrical heating ( 40'C+) or a stove with the flue running through it & a room airconditioner to remove humidity. If the container contains a lot of mass in timber the temp would not fluctuate that much unless the heat was not on for more than a day
regards inter

depending on how mutch u have to spend. u could have a fire heating watter that is pumped threw steel pipes within the kiln. you would not even need a pump if you set it up right.

Originally Posted by weisyboy

only one problem with that arthur.

teh tempriture has to mutch variation causing splitting.

a solar kiln has to be shut overnight to keep the temp up inside

i have done lots of reaserch and have a good desighn i just gotta get round to it.

if ya want it Mathuranatha i can send it to u.

Sure thanks , send it and then i can also feel bad about not getting around to it .

as well as not getting round to fixing the brakes on my old bedford tiper , the starter on my old excavator , the old patrols starter , the old hilux's waterpump and the old landcruiser's leaking fuel tank .the hole in the boat [droped a big rock on it with the excavator when it was still going]

At least my cainsaw ans sawmill are still going so far

gday

i will post a pic when i get organised.

i to have an olds bedford tipper that is in need of some TLC (new starter) but its beyond ever going on teh road legaly again.

we could start a bedford thread in here i have 2 of em , a J3 and a J1 none of them are runners ,
although the J1 could be with a few hours work
both are tray back non tipping , i did have an acco tipper but i sold that

j3 dotn go but it was parked there. just needs a new started and it would run. you wanna buy it

Hey Carl, while you're in the process of sending out the plans for that solar kiln would u mind adding me to the list? I'll PM you with my email addy. thanks.

Originally Posted by weisyboy

teh tempriture has to mutch variation causing splitting.
a solar kiln has to be shut overnight to keep the temp up inside
i have done lots of reaserch and have a good desighn i just gotta get round to it.

Unless a you really push the kiln so that the timber experiences a regular really wide daily temperature variation (eg 35 - 40ºC every day) splitting will not be problem. The reason why (not all) solar kilns are shut at night in Australia actually has little to do with temperature variation and splitting but to help destress the timber. Closing the kiln forces the air humidty inside the container up, and it is also desirable for the temperature to drop at least a little, so the wood relaxes allowing the outer layers of the timber to reabsorb some of the moisture from inside the kiln air, and to help the outer dry wood wick moisture away from the inside of the timber. This does not speed up the drying processes but destresses the timber which is particularly important for Aussie timber. If this is not done the wood becomes case hardened and becomes difficult to resaw.

The reason timber splits inside solar kilns is because users get too greedy and run them at too high a temperature by not providing enough ventilation or internal circulation - this rips the moisture off the outside way too fast and that's what splits the wood. If the kiln is run very hot it becomes even more essential to shut it at night for the reasons above. The other factor that causes splitting is having too little wood in the kiln - the wood acts as a bit of a buffer reducing the temperature variation.

My completely passive drying shed (a seatainer with whirly bird powered ventilation) is not a kiln but it does have good characteristics for drying (faster than air drying, but slower than kiln). It is on average about 7º hotter that the outside air temp in the day, and 5º hotter at night (with an average range of about 20º, the highest I have measured is 27º in one day) I got some splitting when the shed had only a small amount of timber in it, but once the shed was more than half full it worked fine. In teh picture below you can see the temperature (high) and humidity (low) during the day, and the other way around at night, which is desirable. I could speed up the drying considerably by reducing the ventilation but then I would have to close the shed up at night - I live 20 km away, and I don't want to run power to it - I wanted a completely passive system. However, it does take around 6 months to dry a 2" slab in summer and a bit longer if it's over winter. I don't care that it takes that long because I have timber coming out of my ears at the moment. The best and simplest thing I could probably do to help speed up drying it would be to add a couple of internal fans.



For those of you that would like brief plans and details for solar kilns designed and tested by professionals there are designs such as dryer number 5 on this page "www.woodweb.com/knowledge_base/Solar_Kiln_Designs_2.html"
This is specifically designed for the tropics by the Queensland forestry department. it uses a concrete block and corrugated iron box inside a larger black painted structure and a 1.5KW fan for circulation.


There are 3 other pages of solar kiln designs and details of how they work and drying times etc
http://www.woodweb.com/knowledge_bas...Designs_1.html
http://www.woodweb.com/knowledge_bas...Designs_3.html
http://www.woodweb.com/knowledge_bas...Designs_4.html

Kiln design sounds easy but if you build an untested design and load it with a full load of timber (as this is the way it is supposed to operate) the last thing you want is to destroy thousands of $$ worth of timber.