Oven for steaming?

[David Utterback]

I would like to bend a 3/8" thick air-dried cherry board across its width to use as a chair back splat. The bend would only be about 1/2" over a 9" width. Could I steam the board in the kitchen oven using boiling water at the start with the oven at say 250 degrees?

I also need to build a form to compress the board for drying. Would the form work if it was was 3 or 4 uprights of 3/4" thick material that are attached to a base?

I plan to test with a scrap piece. When switching over to the actual splat, would it be okay to cut tenons on the ends before steaming. It would be much easier to cut them on the flat stock.

Thanks for any input.
David

[Bill Dufour]

For a piece that small I would look into soaking instead of steam. Any tenons will expand some due to steaming so the mortises will have to be cut to fit after it dries. I would soak it underwater overnight or longer before bending. Steam is just faster but more complicated. Steam is easier for very long work.
Soaking can be a five gallon bucket and a cinderblock. I would put the cinderblock in a plastic bag so nothing rubs off onto the wood. Or fill a smaller bucket with gravel or stones. Oak in contact with wet iron will turn black. If only water and plastic touch the wood it should not get stained.
Bill D

[Zachary Hoyt]

If you just need it to curl up a bit I would try putting it on a concrete floor for a day or so. This time of year the air is very dry inside and the floor still retains some dampness, so the edges will curl up away from the floor as the top surface dries out. I have inadvertently done this many times, and it can often be reversed by flipping the piece of wood back over and leaving it on the floor again, but if I leave it too long it will curl up the other way. The curve will be across the grain, there is not generally any curling effect along the grain in my experience.
Zach

[johnny means]

Your approach isn't going to create the permanent bend that you want. You may manage to cause a useful bow, but you'll just have a bowed board that will want to return top it'd natural state.

[Tim Janssen]

I'm not sure that it's possible to steam bent across the grain. Tried it once and the wood split on the outside of the curve. Steam bending wood along the grain is normally accomplished by compressing the wood along the inner curve, that's why you would contain the board along the length in a strap while you force it around the form.

[Michelle Rich]

I do believe the board will crack in that orientation. As for steaming, I have used metal guttering on top of my stove for over 30 yrs..yes it would technically be boiling vs. steaming, but it works very well.

[David Utterback]

This experiment has failed and I am at a complete loss to understand why:confused:. I preheated the oven and poured boiling water into a cake pan and then placed the board on the rack above. Since the water did not boil at 250 degrees, I increased the temp to 300 and then to 350 degrees. After several hours, the water still did not boil and vapor bubbles on the interior pan surface never formed. What the hey?!?!?!!!

I am embarrassed to say that I was a chemist in my early career and I understand the relevant physics (at least I think I do). At the highest oven setting, the water temp was 175 using a kitchen thermometer (which may not be accurate). My only idea is that the total mass of the oven absorbed much of the heat from the air and that mass did not exceed the water temp either. Seems a stretch, though.

I will repeat the process today without the board and try the convection oven setting. Any suggestions on the problem would be very welcomed. I will also get a steam box assembled. Thanks!

[Tony Shea]

It is absolutely too much mass to heat that water up to the 212deg boiling temp in an oven operating at 400deg. It would take hours to get that water boiling at oven temperatures. When we boil water on the stove top we are heating the water with a temperature in the thousands, with propane reaching 3000+deg F. That's a massive temp difference with such a large mass of water.

If you don't want to make a steam box you would be better off boiling a trough of water on top of an outdoor propane burner and letting the wood soak in boiling water for a good amount of time, depending on wood thickness. I personally am not sure how long to soak the wood in boiling water as I have used steam in the past and followed the 1 hour per 1" of thickness plus about an extra half hour.

[Richard Coers]

Just make a small steam box and use a tea pot on top of the stove. One of your current problems is an open container of water vs a tea pot. No pressure can build in the open container.

[Thomas Wilson]

David,

Evaporative cooling of the water in the pan and relatively poor conduction from the air to water/metal kept it from boiling.

TW

[Michael A. Tyree]

I just finished a chair using ladder backs from 3/8" osage orange. I use my maple syrup evap pan which is mtd in a rectgular hole in what is essentially a barrel stove used for syrup. I boiled my slats, not a rolling, hard boil (it was cold outside!) but quite close(wood doesn't read temperatures) for 3-4 hours and then my regular bending process is simple enough. While wood is hot!!!!!-> I lay the slats centered on a rough 2x2 oak sq and clamp one end down towards my work bench using a pair of clamps, one on each corner and a stiff board that covers all ends across the width and then another stiff board across the other ends of slats and another pair of clamps, pulling toward the bench top until I like the bend. I did 20" pieces by 4" and lost ~ 1/2 at the most from the curve, not very much. My pattern is one shape only then I adjust the tenons lengths by a dry clamp up of the chair to account for the slight taper of the upper back posts.
A FT chairmaker I knew here in KY, did his the same in a barrel in his shop yard. he used a set-up that had two end pieces with three sq holes in each and some 2x2" sq pieces for the formation of the slight arc. Clamps helped him get the squares in the holes to hold the ladderbacks. I haven't done many ladderbacks before, usually I do round rungs in the back and hickory bark over that frame. In this chair I wanted to shoe off the uniqueness of the species so it got ladderback slats. I've never heard of "splats"?
I don't bend anything else so this work fine for me. On a small childs rocker pattern I always do small ladderbacks from walnut or cherry and about 12" long on that one- I use the same set up.

[David Utterback]

The convection setting did get the water a little warmer but also roasted the wood. It split along the grain when I clamped it in the form. The wood did not seem at all moist when I took it from the oven.

Bottom line: the oven is not a suitable steamer for bending wood.

Thanks for all the responses! I will try a steamer box next.

[Michael A. Tyree]

I use a canner on the stove for my 12" pieces.

[David Utterback]

I just finished a chair using ladder backs from 3/8" osage orange. I use my maple syrup evap pan which is mtd in a rectgular hole in what is essentially a barrel stove used for syrup. I boiled my slats, not a rolling, hard boil (it was cold outside!) but quite close(wood doesn't read temperatures) for 3-4 hours and then my regular bending process is simple enough. While wood is hot!!!!!-> I lay the slats centered on a rough 2x2 oak sq and clamp one end down towards my work bench using a pair of clamps, one on each corner and a stiff board that covers all ends across the width and then another stiff board across the other ends of slats and another pair of clamps, pulling toward the bench top until I like the bend. I did 20" pieces by 4" and lost ~ 1/2 at the most from the curve, not very much. My pattern is one shape only then I adjust the tenons lengths by a dry clamp up of the chair to account for the slight taper of the upper back posts.
A FT chairmaker I knew here in KY, did his the same in a barrel in his shop yard. he used a set-up that had two end pieces with three sq holes in each and some 2x2" sq pieces for the formation of the slight arc. Clamps helped him get the squares in the holes to hold the ladderbacks. I haven't done many ladderbacks before, usually I do round rungs in the back and hickory bark over that frame. In this chair I wanted to shoe off the uniqueness of the species so it got ladderback slats. I've never heard of "splats"?
I don't bend anything else so this work fine for me. On a small childs rocker pattern I always do small ladderbacks from walnut or cherry and about 12" long on that one- I use the same set up.

I have learned that splats are panel backs in chairs. I am able to find examples when I search websites using the term. They are generally attached to the crest rail and a lower rail or seat with tenons.

Were you able to attribute the failed slats to the structure of the Osage orange? Was it grain runout? I have not worked with that wood so I am wondering if the grain is straight.

Thanks again for all the assistance.

[Michael A. Tyree]

I don't have any failed slats or splats? That chair is finished and in my home waiting on Christmas to be given away. Bending one should be picky on the wood used always, more so on the difficult species.
Osage wood has wild grain fairly often but I chose a board to make all 4 slats for my chair with good grain. Indians it's was one of their main bow woods so you know thin pieces can stand up to torture of bending and such.
Often when surfacing osage grain reversals similar to fancy maple show up as pullouts so matters a bunch to take tiny cuts. Of course it's so hard you'll burn up blades if you try forcing things and burn the wood too.

[Tom Bender]

Assuming that you want to bend the wood in the normal way, like a rocking chair rocker;

If your parts will fit into it, prop them up in an electric frying pan. It WILL boil the water and with the lid on it will steam your wood.

Now a couple of caveats;

KD Cherry will be difficult to bend, AD will be slightly easier, green you have a chance.

You need a form that you can clamp to.

You need some extra length on each end as the last 2" will remain straight.

[Mike King]

To bend the wood, you need to soften the lignins that bind the cells and structure of the wood together. The wood needs to reach approximately 190 degrees Fahrenheit to soften the lignin allowing the wood to be formed into a different shape. Methods for heating the wood include steaming, boiling, using hot pipe, or heat blankets.

Michael Fortune has an excellent article on steam bending wood in issue 238 of Fine Woodworking (Jan/Feb 2013). I learned steam bending from Michael, Elliah Bizzarri, and Adrian Ferrazutti at Anderson Ranch. Fine Woodworking also has some good articles on hot pipe bending, as well as bending with a clothes iron.

[Tim Janssen]

It's easy to make a steam box. I use sheet foam to make them and use long deck nails to hold them together.

421601

421602

[Mike Henderson]

For a crest rail with only a 1/2 inch deep curve, I get a thick board and cut it on a bandsaw to the curve I want. I make the tenons first (which will be towards the face of the board) then bandsaw the board to the curve I want. I use a long trammel to mark the curve. I find that MUCH simpler than trying to steam bend wood.

Also, when you steam bend the final shape is never exact - that's just the way steam bending works. But when you bandsaw the final shape is exactly what you want.

Mike

[I can post a picture of some chairs I made that way, if interested.]

[David Utterback]

I don't have any failed slats or splats? That chair is finished and in my home waiting on Christmas to be given away. Bending one should be picky on the wood used always, more so on the difficult species.
Osage wood has wild grain fairly often but I chose a board to make all 4 slats for my chair with good grain. Indians it's was one of their main bow woods so you know thin pieces can stand up to torture of bending and such.
Often when surfacing osage grain reversals similar to fancy maple show up as pullouts so matters a bunch to take tiny cuts. Of course it's so hard you'll burn up blades if you try forcing things and burn the wood too.

Michael,
Sorry, but I did not understand what you said in your 12/08/19 post. "I did 20" pieces by 4" and lost ~ 1/2 at the most from the curve...."

Are you talking about loss of length? Thanks

[David Utterback]

Thanks to all for the responses. They have been very helpful.

Tom: No electric frying pan but I do have an electric turkey roaster that is the intended steam source for the final setup. I have taken your suggestion and just steamed the splat using quarter-sawn cherry this time. It quickly produced steam between 210 and 215*F. The piece it is in the form right now.

Tim: I saw your steam boxes in an earlier post on bending cherry. I stole the idea I liked it so well. The styrofoam board that I used distorted a lot. I can see the brand you used but have not located a local source so far but I am sure it is out there. The system heat loss using the form is much less than other materials such as exterior grade plywood.

Mike H: Your bandsaw suggestion is what I have done for convex side of the crest rail and will do for the bottom rail from the same 8/4 piece of cherry. But my skill level does not give me a fair curve so I have to do hand shaping with spokeshaves and scrapers (good learning opportunity). I will cut the tenons as you recommend but also want to cut the splat mortises before slicing out the curved rails. Hence I need to get the splay shaped first.

Mike K: Thanks for the references. I have the FW source on my shelves and will check it out.

Thanks again to all of those that responded. All comments have been helpful. I love this site!

[David Utterback]

The turkey roaster worked well. It was only $40 so cheaper than the woodworking store steam source and the temp is adjustable. It's flexibility as a stock steamer is a bonus. It can manage stock as long 17-1/2" long and up to 11-1/2" wide suspended on the roaster tray that was included.

Also, the quarter-sawn cherry had less spring back than the flat sawed stock. Since I want the grain of flat sawed cherry in the splat, I will deepen the curve on the form. Hopefully, not much trial and error will be needed.

[Bill Dufour]

I recommend polyisocyranarate (sp) foam board over styrofoam. The box stores often have some broken pieces for reduced prices.
Bill D