drying bowl blanks?

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Forum topic by SCOTSMAN posted 03-25-2013 06:28 PM 4391 views 2 times favorited 8 replies Add to Favorites Watch
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5849 posts in 3585 days

03-25-2013 06:28 PM

I am an avid but only occassional woodturner due to poor health.I would like owing to the high cost of bowl blanks be able to dry the many green bowl spindle timber I have here available on my garden.I have avery good ebac dehumidifier a real professional set up how could I use this to dry the green timber I have for bowl turning we are only talking about relatively small pieces uo to eight/ ten inches or less.Does anyone here have the knowledge or point me in the right path for info or a book dvd to make such a nice small kiln I would love to try this as the dehumidifier is just sitting here doing little else.
here is the exact same type but not my own machine as this one for sale on ebay ! Alistair

-- excuse my typing as I have a form of parkinsons disease

8 replies so far

View Built2Last's profile


234 posts in 3478 days

#1 posted 03-25-2013 06:57 PM

I built a box 4 feet high, 4 feet wide and 12’ long out of wafer board or either plywood would work, it doesn’t have a bottom, just sitting on concrete floor. I lined the inside walls, ceiling and floor with plastic, then to keep the plastic from tearing, I put scrap pieces of tin around the inside. I have just a regular dehumidifier in it with a hose ran outside and I also run a oscillating fan inside. The dehumidifier and the fan create enough heat to get it around 105 degrees inside. I can dry around 500 board feet of pine in 2 weeks or less or 500 board feet of hardwood in about 4 weeks down to 8 percent moisture. You may not need one that big but scaling it down would probably make it even more efficient since you have a good dehumidifier. I tried running the new style dehumidifiers with a digital control panel and they wouldn’t last but 2 or 4 loads and die. Then I found some old style units with just a couple of knobs on them really cheap. I bought 11 thinking they wouldn’t last either. I’m running the first one still and it’s been almost a year. I just put some cherry and sycamore in it this past weekend and there is almost a solid stream of water running out the pipe. Also, I really can’t tell a difference in my power bill even with it and the fan running 24/7. Since mine is inside I didn’t bother insulating it. The plastic helps keep it from drawing moisture from outside the box. I made it as air-tight as I could. Hope this helps.

View Wildwood's profile


2306 posts in 2135 days

#2 posted 03-25-2013 06:59 PM

All you need for a homemade kiln is a box, heat source, and air circulation. This site will give you some ideas so can build to meet your needs.

Some more food for thought:

Also some examples right here at this site.

Good luck!

-- Bill

View NGK's profile


93 posts in 1911 days

#3 posted 03-26-2013 03:11 AM

What you have described is a good way to dry flat stock, otherwise known as boards. However, when drying chunks large enough for bowls, your speed or rate of drying is too fast for the size of stock. You’re going to get a lot of cracks in the outside (perimeter) of bowl blanks. SLOW is the key here.

In fact that’s why bowl makers turn the object with a thick wall, stick it in a brown paper bag, and wait about 6 months for it to ‘slowly’ dry. Removing most of the stock from the blank which becomes the bowl allows the stresses from the drying process to equalize out or balance better. Or, said another way, the “inner” moisture is now near the outer shell and less likely to crack.

Chunks of wood lying around outside in the Central or Midwestern states will come to an EMC (Equilibrium Moisture Content) of about 15 percent, due to the average relative humidity in that 10-state area. It’s the overall average of “high at night” and low during the day OR “high on rainy days” and low on non-precipitation days.

Your finished bowl project needs to be under 10 percent moisture to avoid cracking in your house during the low humidity of forced air heat in the Winter and air-conditioning in the Summer.

View RussellAP's profile


3104 posts in 2287 days

#4 posted 03-26-2013 01:26 PM

I just built myself a kiln for drying bowls.
First, you’ll notice right off that some woods dry better than others. By that I mean that some will crack and others wont. That’s the wood, red elm is a cracker, box elder is stable. You just have to learn which is best to turn wet and which dry.

Principles of drying blanks;
Use a wood stabilizer like Pentacryl. Get them wet with this and put them in a large ziploc freezer bag and keep recoating it every couple hours for as long as the recommended thickness of the wood. I turn green and then use this product, it’s not needed if you turn dry. Really helps the bowls dry out quickly with out warping or cracking. Great stuff.

IMPORTANT: Air drys, heat cracks and warps.

My kiln puts the lights/heater at the top and draws down the air to the shelving below.
The air in the light/heat box is hot with radiant and convective heat which will heat the air causing the humidity to lower. The air is then pulled down, not up because heat rises and it’s hard to control with heat on the bottom.
This method will dry the air without heating it much above 80-85 degree F which is 26 -29 C.
Then you want the air to gently move around the bowls for about 4 days. You don’t want a wind tunnel, just a nice gentle air flow which is almost undetectable.

If you are unsure about the moisture content, you can use a meter or do what I do. Sand a spot down and see if it discolors in an hour. If it does, it’s still wet. Also you’ll be able to tell by weight.

Some of these jocks will tell you you need a certain moisture level to prevent cracking, but the point isn’t to bring the bowl to 8% moisture, it’s to get the moisture out of the deep pours, and the stabilizer does that by pushing the water out of the fibers and replacing them with something that doesn’t dry out the fibers so quickly that they contract causing warping and cracking.

So remember, slow air flow and just a bit of heat will do the trick.
The dehumidifier will be good in the room, but don’t hook it up to the kiln in any way because it’s just too aggressive.

Hope this helps you out.

Here is picture of my newly built kiln, it’s not attractive but it’s functional.

In this set up, the wettest bowls go on the bottom shelf and move up as others are taken out. It gets progressively warmer as you go up. The first chamber with bowls in it is 26 C and the next is about 24 and the next is 22 or lower. The lower bowl gets more air flow, the upper bowls get more heat. So about 4 days is all it takes to bring a wet water flinging bowl to a workable piece.

Message me if you need any advise not given here.

-- A positive attitude will take you much further than positive thinking ever will.

View Nomad62's profile


726 posts in 2958 days

#5 posted 03-26-2013 03:30 PM

Pentacryl is as good as stated, it really helps even very highly figured woods hold their shape as they dry. Somewhat of a cheap insurance policy. If it is not an option for you, then drying slowly as mentioned above is key.

-- Power tools put us ahead of the monkeys

View Wildwood's profile


2306 posts in 2135 days

#6 posted 03-26-2013 04:09 PM

If can find “Fine Woodworking on Wood & How to Dry IT, “ by Taunton Press

Several short articles can read only thing not covered is roughing out bowls and setting aside to dry.

If can find a copy of Richard Raffan’s “Turned-Bowl Design published in 1987 by Taunton Press walks you through harvesting wood, rough turning, and drying. Raffin has a newer book out “The Art of Turned Bowl Design.” Have not read new edition so not sure what it contains.

Drying wood at home more art than science. Have found end sealing and air circulation more important than heat. I use paraffin wax or latex paint as an end sealer. As long as turning wood out of the weather with good air circulation will reach EMC eventually. Homemade kilns a good op for speeding up the process but there is a learning curve.

I do not use stuff like pentracryl or end sealer after roughing out a bowl blanks. Depending upon MC, may or may not wrap a bowl blank in newspaper, grocery paper/plastic bags. Do cut my logs little longer just in case end sealer fails. I do not split spindle blanks under 6 inches, but do for over six inches. Have to adjust your schedule & approach based upon average annual relative humidity for your part of the world.

-- Bill

View NGK's profile


93 posts in 1911 days

#7 posted 03-26-2013 06:58 PM

Wildwood—paragraphs 2 and 3 above are well-stated. I, too, have used paraffin wax (expensive), and latex paint (2 coats is better), and end sealer, but did not mention them in my post. I avoid plastic bags to prevent mold if it’s warm enough.

View Wildwood's profile


2306 posts in 2135 days

#8 posted 03-27-2013 09:55 AM

I live in zone 5 is the worst for log mold and staining in US. Have no idea how that works in Scotland. Only use a plastic bag while turning if stopping to go eat. Certain times of the year worst than others.

I can buy inexpensive box paraffin wax from military commissary or grocery store in town here. Ask if they carry canning wax. Gulf is brand name sold around here. Now do believe in wax emulsion end sealer products like anchor seal and green wood sealer. If did not have to pay shipping cost might try some.

If understand wood shrinks as it dries products like Pentracryl, Cedar-Cide Turners Choice, not necessary. Not sure can buy Turners choice any more Cedar-Cide web site not up and running.

People really concerned with wet wood cracking should look into PEG 1000. Only works with wet wood with MC of 30% or better. PEG 1000 does not work with some species of wood nor dry wood. See instructions at Lee Valley or more complete information provided by Oregon State link.

Ed Moulthrop, now deceased his son and grandson use PEG. Moulthrop’s mention using it in their book “Moulthrop Legacy in Wood.”

But, wait there is more to this rumbling and mumbling! I do not advocate woodturners start using PEG to treat their wet wood. Like other wood treatments products devil is in the details. I provide you those details in links provided!

-- Bill

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