Kiln

[Bernie Weishapl]

I am looking at building a kiln from a old freezer. I have seen several plans out there and have a plan in mind. With that said I noticed that some have vents and some say they have vents but don't open them. My question is should there be vents that allow the air to flow or not? I would think you would want to get rid of the humidity in there somehow.

[Bill O'Conner]

Not sure about a vent as long as you can keep the air moving inside you should be fine

Bill

[Ken Fitzgerald]

Bernie,

I"d think you'd need some small vents. As the wood dries, the humidity level in the freezer would increase. Once there was an equilibrium, I'd think the drying process would stop or creep to a very long drying time.

I'd think some small vents would be in order.

[Brodie Brickey]

The moisture has to go somewhere or you will have spalted mold. Great when you want it, but when you don't?

I believe that they use a small vent with a 60 watt bulb if I remember correctly.

[Steve Schlumpf]

Haven't built one nor have I seen one in use but have to think that a small vent (at the top) would be required as a means to get rid of the humid air. Does that mean you also need a small intake vent (at the bottom) to provide fresh air?

[Roger Wilson]

I am looking at building a kiln from a old freezer.

Unless you already have a fridge dedicated to this I'd consider making the kiln out of plywood and styrofoam insulation. You can customize it much more easily then a fridge. See link below for several articles on doing this.

http://www.woodturningonline.com/Turning/Turning_articles.html#drying

[Don Carter]

Bernie:
But what will you do with the ice cream?

Seriously, I saw one of these on the web somewhere, I think they were vented bottom and top.

All the best.

Don

[Barry Richardson]

I was over at a bowlturners house the other day, and he used old dishwashers for dryers. Pretty slick, they already have pull-out racks for the dishes that work great for the bowls, he says he puts a 100 watt bulb in it and just leaves the door cracked slightly. he has several in his back yard, and writes the batch date on each one to keep track of how long they've been drying.

[Tony Pridmore]

A few folks in our turning club have gone with the dishwasher approach. I think they got the idea from Russ's Corner: http://www.woodcentral.com/russ/russ8.shtml

[Bernie Weishapl]

Thanks to all. I already have a freezer so that it not a problem. I probably won't start working on it till summer because it is in a unheated garage. No room in the shop.

[Richard Madison]

Ok, I'm confused. Many folks are trying to slow the drying of roughouts by sealing the endgrain, bagging with wet shavings, etc. Meanwhile others are apparently trying to speed up the drying by putting stuff in "kilns". Presumably the goal of slowing the drying is to prevent/reduce cracking due to unequal moisture loss (and the resulting unequal shrinkage) from contiguous areas of the roughout. Seems like faster drying in a "kiln" would exacerbate the problem.

Would someone please 'splain this?

[Jim Kountz]

Ok, I'm confused. Many folks are trying to slow the drying of roughouts by sealing the endgrain, bagging with wet shavings, etc. Meanwhile others are apparently trying to speed up the drying by putting stuff in "kilns". Presumably the goal of slowing the drying is to prevent/reduce cracking due to unequal moisture loss (and the resulting unequal shrinkage) from contiguous areas of the roughout. Seems like faster drying in a "kiln" would exacerbate the problem.

Would someone please 'splain this?

Richard, drying bowls in a kiln is a common practice and an absolute necessity for some like production turners. These guys turn bowls out at such a rate that sitting around waiting for them to dry would cost them too much money in the end.
That being said its a very exact science actually, you want to draw the moisture out of the roughed blanks as efficiently as possible yet do it without causing defects.
In the first stage of kiln drying you want as much humidity in the enclosure as possible, the inside of the kiln will literally drip water. Usually there is only fans going at this time to circulate the air in and around the bowls. Your goal here is to get all the bowls to reach equilibrium moisture content. Once that has been achieved you can start applying more heat to wick the moisture from the surface of the blanks. As the water on the surface of the bowls is wicked away and evaporated more water from within the bowls will come to the surface. Humidity in this example if your friend as it keeps the wicking process under control so it does not occur too fast.
Most of the guys Ive talked to who do this successfully have taken the time to develop a specific operating schedule for THEIR kiln. I know of a guy who uses a small cabinet in his shop with a light bulb in it and a small fan. He runs the fan for a week, then brings the temp up to 70 then 80 then close to 100 and he has a pretty high success rate. Its a small enclosure though. Mine is 4w x 4l x 5 h. So in my test a single light bulb was not near enough to bring the kind of temps I need so I have 4- 200watt bulbs and two small bathroom fans ducted to 4 separate air vents within the kiln. The lights are on a thermostat and the fans just run all the time although they are on a switch should I find the need to shut them down. I can take my kiln to 100 in about 3 hours. I will never need to take it that high, that fast but I needed it to be able to reach those temps in an unheated area.
Mine is 2x3 construction, insulated with plywood interior and osb exterior. Painted inside with a good marine grade paint. The thermostat is for greenhouse use and can take the higher levels or moisture. The fans are bathroom fans and are also use to humid conditions. I could go on forever here but Im going to do another post later with a play by play of the actual operation.

[Allen Neighbors]

Hi, Bernie. I have three "Referkilns". I use a light bulb in each compartment... 25,40,60watts depending on the size of compartment. Also, each compartment has a circulating fan(the one that was in the fridge). The fan just circulates, it does not exhaust.
I have a dozen or more 1/2" holes in the bottom, and the same number in the top.
The theory behind the holes is that the heated, moist air rises, and escapes through the top holes, pulling fresh, dryer air in through the bottom holes.
When I put a roughout or blank in the refer, I use no electricity for the first week. The second week, is fan only for about 8 hours per day. The third and fourth week is alternating light and fan (about 8 hours per day). Then just light for another week. They get pretty dry by that time. I gauge the moisture level by a "kiss", because I don't have scales and/or a moisture meter. Win some, lose a few.

[Richard Madison]

Thanks Jim and Allen.

[doug young]

bernie,
I know my dad keeps a can of dessicant in his gun case to reduce the humidity. I am not sure if it is applicable but there are kinds that absorb humidity and change color when saturated then you can put them in your kitchen oven on low and dry them back out to use again. I think it is pretty cheap and a couple coffee cans might be enough. In thinking about how not to need vents this is what came to mind.

here is a link for the stuff
http://www.agmcontainer.com/desiccantcity/desiccant_faqs.htm

doug