Heat Source Boiling Bowls

[John Nordyke]

For those of you who rough turn and boil bowls to reduce cracking, what do you use as your heat source for large containers?

I have been using a propane burner and stand (from a turkey fryer) on top of which I place a large cast iron pot. I've looked at DIY rocket stove plans (for the intense heat, not because I need to be super efficient in my use of fuel wood), but haven't seen any that look like a good combination of easy-to-build, sized for a big boil, and no need to attend constantly to feed more wood.

Suggestions/plans welcome!
JN

[Chris A Lawrence]

Go electric. My other hobby is home brewing. I use an electric boil kettle that has a hot water heater element mounted in it. You can get a controller for it that works on a duty cycle it pulses the element on and off to control the boil. The longer you set the duty cycle the longer it keeps the element on during the pulse.

[Timothy Thorpe Allen]

What is it about the propane burner that has you looking for alternatives?

[John K Jordan]

Jim King (now deceased) from Iquitos, Peru, exporter of bowls and blanks of some amazing wood told me they always boiled in 55-gal drums over a wood fire. Some of the wood he sold had a huge likelihood of failure without boiling.

When I boiled I used a turkey fryer with propane. Not useful for large bowls.

Expert Stephen Russell wrote this in his boiling article:

I prefer to use a 55-gallon drum for the boiling pot. This has been cut down to 18" high. The pot is heated with a Cajun-style propane burner, which is typically sold to fry turkeys or boil seafood outside. If you live in a rural area, you can easily heat your pot with scraps from your studio. Whatever container you decide to boil in, use a pot that you can dedicate exclusively to timber boiling. The extractives in the timber will quickly make a mess of your boiling pot and you will not want to use it for anything else.

stephen_russell_boiling.jpg

In the past, I boiled my rough outs with a full rolling boil for the entire boil cycle. I found out that this was not necessary and just wasted propane. Now, I bring the pot up to a boil and place the bowls and platters into the "soup." You need to produce an active medium boil, not a simmer. A full rolling boil can also be used, but it does not generate any increased

You must monitor the pot to insure it does not boil dry. Periodically, you will have to replace some of the water lost during the boil. I replenish the water in between boil cycles to prevent any compromise of the boiling cycle. You can also cover the pot with a lid to help retain heat, water and conserve fuel. The boiling water may slosh out and stain some surfaces, so take precautions to insure that you have suitable protection.

All pieces in the boiling pot must be submerged during the boiling process. A simple grate can be made of concrete rebar scrap that is wired together and will fit inside the boiling pot. A weight is then added to insure that the grate keeps all pieces submerged during the boiling.

CAUTION: Do not load pieces into your pot that are near the same size as the maximum diameter of the pot. When the wood takes up water during the boil, it will expand in size. If the piece is near the same size as the pot’s diameter when you place it in the pot to boil, the wood will swell, creating a tight fit, or plug in the pot, causing a build-up of pressure under the plug. This is a dangerous condition that can cause severe injuries. For safety, always allow 6" of free space around your boiled pieces in the pot as a safety margin. For example, if your pot measures 24" in diameter, the maximum size piece you should ever boil is 18". If you need to boil larger pieces, get a larger pot, observing the 6" safety margin.

Stephen has much more useful information on boiling including his methodology and results of exhaustive tests. Unfortunately his web site and library of articles is no longer available except on the "Wayback Machine", the internet archive.
https://web.archive.org/web/20171003...-articles.html
The archive is slow to navigate but everything is there. I copied much of it to my local storage for quick access.

If you find the propane sold at consumer outlets for grills too expensive you might get a better price elsewhere. We use propane for our gas kitchen range and I use double 100-lb tanks, carry to a gas supplier for filling.

JKJ

[Peter Blair]

For years I did similar to you but I used a big Canner. I would like to warn everyone that wood CAN burn under water. I would use a weight to hold down the piece(s) and one time I had turned a recess in the bottom of a piece of Oak and I guess it fit tightly to the bottom and after the water that was trapped under it boiled away it burnt the recess bad enough so it was unusable.

[Reed Gray]

I guess it would depend on what type of volume of bowls you are talking about. Dale Larson, who does a lot of madrone bowls used to use a galvanized horse trough with a couple of propane burners under it. I knew another turner who would steam rather than boil. I think you had to steam longer than you boiled, but not positive about that.

robo hippy

[Leland Frayseth]

Thank you JKJ for the link to this great article. I think I need to boil my Pecan bowls after reading this article. The author did a thorough job of keeping statistics and comparing boiling versus paper bag. I needed this timely information. Leland

[John Nordyke]

Thanks for replies so far. My only complaint with the propane setup vs wood burning is that propane isn't free That's why I was hoping for good plans for a simple rocket-stove type solution (brick or metal, but I don't have metalworking tools or skills).

[Bill Jobe]

I'm not well read on the op's subject. Anyone try a pressure cooker?

[John K Jordan]

Bill, according to those who boil a pressure cooker will work well but quite limited in size compared sometime the size of a 55-gal drum. BTW, I understand the boiling softens the lignum and allows stresses in the wood to equalize, the combination nearly eliminates much of the movement and cracking by drying. After boiling, the drying can be by any method. Back before I graduated from bowl turning I just put some on the shelf and had zero defects.

As for burning the wood, a bottom grid of some metal or wood might help keep the bottom bowl away from the bottom of the container. I have sheets of expanded stainless steel that would work. Also, read what Stephen writes about turning the heat down.

Leyland, check out some of Stephen Russell's other articles, both in his main articles section and his tips section. His web site was one of my primary resources for years until it disappeared. Thank Goodness for the internet archive! I save the articles as HTML files on my computer's hard disk.

John H., road trip! I have metal working things like welders and plasma cutters and I'm not afraid to use them. A coupie of years ago I found a source of inexpensive dented stainless steel 55-gal drums (usually VERY expensive) which is what I would look for if making a boiler today. A good stand to support the drum would be easy to make. Look into getting propane directly from a gas company rather than refills on small tanks. If you have natural gas available, that would be another option. I have a friend who has a 2" gas line to his pottery studio for firing huge pots! If there is natural gas in your area but not at your house the gas companies will often run the lines for no cost.

JKJ

[Ralph Lindberg]

I guess it would depend on what type of volume of bowls you are talking about. Dale Larson, who does a lot of madrone bowls used to use a galvanized horse trough with a couple of propane burners under it. I knew another turner who would steam rather than boil. I think you had to steam longer than you boiled, but not positive about that.

robo hippy

Steaming used to be very popular around here, but you can "temper" the wood rather easy, just like pressure cooking . I had a long chat with Dave about both (vrs boiling) some years back.
It's harder to over heat the wood with boiling

[Ralph Lindberg]

I'm not well read on the op's subject. Anyone try a pressure cooker?

Cook woods uses a commercial pressure cooker

[Jeffrey J Smith]

For the past several years I’ve used an enormous heavy duty aluminum stock pot - 24” diameter x 24” high on a jet burner for a crab or turkey cooker. works well for anything 23” or smaller (see warnings on getting bowl and pot diameters too close to the same in many old forum posts. The stock pot was found in the scratch and dent section at a restaurant supply store and was reasonably priced compared to what I found on line.

[Bill Jobe]

3 or 4 years ago I cut down an OO tree, hauled it home, and that night I cut about a 2.75" slab, microwaved it, sanded it down and finished it. It has cracked very little since, but I'm wondering if, had I boiled it after microwaving it, it may not have cracked at all.

[John K Jordan]

3 or 4 years ago I cut down an OO tree, hauled it home, and that night I cut about a 2.75" slab, microwaved it, sanded it down and finished it. It has cracked very little since, but I'm wondering if, had I boiled it after microwaving it, it may not have cracked at all.

I don't understand the logic of microwaving a large chunk of stable wood like osage.

I have experimented with using a microwave oven to dry small pieces of wood such as cherry and it took many cycles of heating for a short time then cooling for a long time. I weighed the wood each time after it cooled completely - when the weight quits dropping the wood is dry.

I have processed a bunch of osage into turning blanks and it seems to be naturally fairly stable. If I cut away the sapwood the wood blanks rarely crack. Osage has no open pores - they are all packed full of tyloses so moisture can't escape quickly like some other species. The sapwood shrinks more and more quickly than the heartwood so that's where I see cracks.

The purpose of microwaving is generally to dry wood. The apparent advantage of boiling is to prevent or minimize cracking while drying. Based on that it would seem if you are going to do both the wood should be boiled first. As I wrote earlier:" I understand the boiling softens the lignum and allows stresses in the wood to equalize, the combination nearly eliminates much of the movement and cracking by drying. After boiling, the drying can be by any method." But from what I've read boiling is mostly used only roughed out bowls. If you do boil a large chunk, note what Stephen Russell recommends "1 hour (60 minutes) of boiling for every 1" of wall thickness." I've bought blanks of boiled madrone burl (4"x4") but I have no idea about how long it was boiled.

JKJ