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Thoughts on possible D.I.Y. Kiln

Al Chavez

Al Chavez

Joined
Jan 13, 2021
Messages
158
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293
Location
San Antonio, TX
Website
www.instagram.com
I’ve been playing around with a small lathe and I’m considering a larger one. Both flatwork and lathe work seem like they would benefit from being able to kiln dry wood. I am starting to consider a wood drying kiln for prepping both lumber and wood turning blanks and roughed out bowls/vessels.

I just found this in CraigsList and it seems like it would be an easy mod to make a kiln from it. It is an all aluminum cage for transporting animals.

I am seeing a wood drying kiln.

Any thoughts? Especially critical thoughts or ones on what I may need to do to modify this. I am thinking foil faced foam insulation, either inside or outside, with or without a framed up box over it and then some heat source. Any suggestions on heat source? Thermostat?

Is this a step in the right direction of becoming a serious turner? I'm very new to turning and splitting on my blanks and pieces seems to be an issue.

Any suggestions on doing this or should I keep looking for other options?

Here are the pics and the dimensions…..
48” x 29” x 33”

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Thanks in advance.
I'm very excited to be in this community.
Al
 
I'm not impressed by that box. Personally, I think that it is a waste of time to have a kiln for turning blanks in central Texas. It is a lot less work to rough out the bowls while the wood is still wet and then either Anchorseal them or use paper bags to slowly air dry them for two or three months.

Drying hardwood lumber requires that the wood be stickered and weighted down which wouldn't work very well in that box.
 
I guess the question is "to what end?" If you are thinking that you need to dry sections of log prior to turning them then you need to look into the much more typical process of twice-turning pieces, where they are rough turned while green to a uniform thickness and then remounted for final turning. Most of us just air dry things for that, it takes 6-24 months, but most turners accumulate more rough turned bowls over time than they will ever have time to finish. Thoroughly drying thick blanks takes a really long time (years), is often unsuccessful because of cracking, and makes the turning much harder. Often the problem in this process is drying too fast, in which case you might need an "anti-kiln", some way to regulate the humidity and slowly lower it over time.

If you are making fine boxes and such that require perfectly dry wood to get good fits starting with kiln dried or well-equilibrated air dried wood then the kind of chamber CIndy Drozda uses will serve well-- she has an old freezer with a small heater in the bottom and a small vent to allow some circulation that she puts wood into for a couple weeks to ensure that it is completely dry.
 
Al Chavez said:
Is this a step in the right direction of becoming a serious turner? I'm very new to turning and splitting on my blanks and pieces seems to be an issue.
Click to expand...

that is tough question. I first heard of kiln drying from a a very serious production bowl turner who was doing kiln loads of 200 bowls every 2 months.

Most serious turners who are not production turners don’t need a kiln unless the live in a very humid climate.
I dry my bowls in a room that keeps the humidity at 50%. what most of us do is turn our wood green before it cracks. Bowls and hollow form with relatively thin walls are turned once and warpage becomes a feature, traditional bowls are usually turned twice rough turned with relatively thick walls, dried 6-12 months and then returned to take away the warp distortion.


more to your issue of working with green wood.
I started a thread in the tips and techniques. On working with green wood. It is from a 90 minute demo I do.

The first part is a set of slides that cover wood movement, wood storage, working with wood before it cracks..
Then there is a video of rough turning a bowl for drying and a video mounting am returning a dried bowl.
https://www.aawforum.org/community/index.php?threads/working-with-green-wood.11626/
 
Thanks everyone for the great feedback.
It seems as if the consensus is to pass on the build with this aluminum box even if I decide to build a kiln at a later date. Hockenbery, thank you for the slideshow presentation on rough turning. That was one of the first posts I read and watched as soon as I joined this community. There is a lot of great info in that presentation. Along with drying and preventing checks/cracks in bowls and blanks, one of the issues I am trying to resolve is insects within green wood.

I had thought that a kiln that can hold temp at 140 degrees for an extended period of time was the solution. I have not seen very much info online that deals with the bug issue. Also, I've just recently read a bit about what Roger Wiegand mentioned about slowing down drying (anti-kiln) and that was a bit confusing because it runs counter to what I've thought about drying bowls and blanks. I was hoping a kiln might be a silver bullet for some of the issues I haven't been able to correct yet.

I'll keep reading and researching here and online.
Again, a big thank you.
Al
 
Drying wood so that it won't crack, or so that you get fewer cracks is an art. Every wood species has different idiotsyncracies, which means that you can't always mix and match when drying lumber in a kiln. 140 degrees can be too hot for some woods. For me, I turn to final thickness, about half an inch, and let them warp. A number of people have converted old freezers and fridges into blank drying kilns. Mostly it is a light bulb in the bottom and the heat from that flowing up and out the top. This does speed up the process. Only turner I know of who uses a drying kiln is Glenn Lucas, and he turns a lot of bowls. He even bought one of those portable bandsaws to slab up his logs, since he goes through so much wood. For me, if I was twice turning my bowls, I would invest in sealer and more shelves, and just let them air dry. For very small runs, you can speed it up a bit in the microwave, but not the one in the house or you will get in serious trouble. Short bursts and let them cool.

robo hippy
 
Hockenbery and Bill Boehme,
I keep coming across your replies in similar threads. Thank you both for your great input. Bill, I've read more about your thoughts from another thread and its beginning to make more sense to me.
"A properly designed kiln dries the wood at a precisely controlled rate that might be faster or slower than air drying. Drying wood is a complex process. If dried too fast the wood will be case hardened. It may not have cracks, but case hardened wood has high internal stresses. When you finish turning case hardened wood it will change the balance of internal stresses and the result will be further warping and possibly even cracking.

All of the pieces should be at approximately the same high moisture content when loaded into the kiln and the kiln shouldn't be opened until they all come out at the same time."

Case hardened wood sounds like impatience creating more even more issues.

Robohippy, thanks for the great info. I am having to rethink my process (which only has a half dozen pieces and another half dozen split blanks). Ha! I'm going to look for some of your youtube videos later today. For now it looks like sealer and shelving in my storage shed (plus patience) might be the route I go.

Mark, I've actually bought four gallons of Dry and Dry and will be trying that out soon.
My pieces so far have been handles for lathe tools, segmented bowls (kiln dried wood), bowls and boxes from green wood (splits) and a lot of blanks that split (will not be making blanks with the pith in them anymore). I recently got into turning with a used Rikon for a great price (came with three sets of tools and some nice accessories) but I've bought a lot more chucks and other accessories and want to do bowls and vessels. I'm looking at buying either a Nova Saturn or probably a Powermatic 2014, they are both in the same price range but the PM is looking better as an option for me. Of course I want to deal with these issues and get a good process before I do that.

My flatwork was becoming not flat and I think turning is the next step.
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You can see my pieces want to be round.
The pieces I've turned are absolute beginners pieces because its all new to me. I'm just trying to make sure I can create pieces that don't crack or warp too much before I pull the trigger on the new lathe. Becoming more patient seems unavoidable with turning. I like that I can finish a piece in a few hours compared to flatwork which might be a few weeks but I am learning that the drying process can't be rushed (at least too much).


Thanks everyone!
 
Last edited:
Thank you Mark!
For both the compliment and the excellent link on the silicon bead drying. I've bookmarked it (and about another dozen great discussions here). Now off to google "therming"!
 
I am a great believer in a small kiln Al. In a thread a few years ago, I showed some stats of the drying process in my kiln. https://www.aawforum.org/community/index.php?threads/my-kiln-build.13214/ Chart is near the bottom of the thread. An article I wrote years ago on mine is at http://www.ghwg.ca/techniques/Mike_Brazeau_Simple_Drying Kiln.pdf When I do not have enough to fill it, I take some of the wet shavings and put them in a plastic bag partial open so it provides additional moisture for the first stage of drying. People use dishwashers, fridges, upright freezers. I have a pdf of a presentation on wood processing I did for several guilds in our area about five years ago. If you Message me I can send to you. Life is bigger than bowls and it is easy to produce lots of good spindle blanks with or without a kiln.
 
Thanks Mike,
I have started a conversation with you about the wood processing pdf you've mentioned. I'm not sure if that is the same as messaging someone but I don't see an option to send a direct message to someone.
 
Al Chavez said:
Thanks Mike,
I have started a conversation with you about the wood processing pdf you've mentioned. I'm not sure if that is the same as messaging someone but I don't see an option to send a direct message to someone.
Click to expand...

Al, private conversations have there place, but it is courteous to keep many of these topics out in the forum for others to learn from.

My kiln is a repurposed wooden shipping box that I covered in a layer of insulation (like someone might insulate a metal building with white plastic sheet on one side and reflective aluminum on the other side). I made the shelves removable so I can dry longer boards as needed. Added two holes on top can be blocked off as need to control moisture loss. As for climate control, suggest using controls for green houses that are built for moist environments. https://www.acfgreenhouses.com/climate-controls.aspx
 
I use a “kiln” but for drying oil or poly finishes not wood, used in cold/cool outside temps. Simple vented box with a light bulb. I would recommend separating flat lumber and turning wood processes. Lots of info out there on various flat lumber kiln designs with different energy sources.

Once “over the hump” of having inventories of wet , rough turned drying, and dry rough turned project stock, the question of drying faster tends to go away. I started out doing a lot of 2 turn work but have migrated to more 1 turn work, which may dry in a few days to a couple of weeks. No matter what method you choose to dry projects (sealer, bags, boxes, whatever) one thing that really helps is to place them in a climate controlled area so that the environment variable is something you dont have to worry about as you develop your drying method. I use wire shelf racks inside the climate controlled house.

I have on occasion used the microwave when I forgot a present or something and didnt have time to wait, but its the exception not the rule. Ive considered the desiccant approach, and its a lot of hassle, increased expense, and limited throughput (unless you buy lots of expensive beads and an oven to regenerate) vs my bagging method. I prefer having some patience and just let things dry more simply and slowly. I try to keep spindle blank stock, 1-1/2” sq up to ~ 2-1/2” sq, for tool handles, from logs cut up for other shapes. Generally it isnt completely dry, but I rough it out and mw it if Im in a hurry. I do some lidded boxes, s&p shakers and the like. I twice turn those, either bagging or mw to dry.
 
Fantastic reply Doug,
As a newbie I am exploring options before I pull the trigger on a larger lathe and you've shared quite a few.
I had not thought about using a kiln for drying oil finishes on my flatwork. I might have to experiment with that as well.
Thank you Sir!
Al
 
Al Chavez said:
I had not thought about using a kiln for drying oil finishes on my flatwork. I might have to experiment with that as well.
Click to expand...

Most finishes have an acceptable temperature range for drying. Using higher temperatures may run the risk of drying defects such as bubbles in the finish. Additionally, varnishes and oils don't "dry" by evaporation ... instead, they are reactive finishes that "cure" by either crosslinking or other chemical reactions. It is a slow process that takes a week or two to cure even though the finish feels "dry" to the touch.
 
Bill Boehme said:
Most finishes have an acceptable temperature range for drying. Using higher temperatures may run the risk of drying defects such as bubbles in the finish. Additionally, varnishes and oils don't "dry" by evaporation ... instead, they are reactive finishes that "cure" by either crosslinking or other chemical reactions. It is a slow process that takes a week or two to cure even though the finish feels "dry" to the touch.
Click to expand...

Correct. Based on the “smell test”, increasing temp (up to ~100F) with some convective are flow seems to speed curing, and speeds up drying considerably when the shop is 65F. I give the pieces several hours or overnight to flash solvents and wipe off bleed out before exposing them to heat. I check within the 1st hour or 2 for more bleed out. When its hot out just placing them outside (use shop ac) does the same thing.
 
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