Boiling kiln dried wood for bending & carving
desodad
| Posted in General Discussion on
I tried recently to boil kiln dried cherry, about 9/16″ thick for bending and then carving. I got the idea from the Curtis Buchanan article on carving spoons with a crank. This did not work me! I know that he used green wood for these spoon blanks, so there’s one problem, but is this even possible with kiln dried stock? I “boiled” at about 200° as I’m at high altitude and did this for about 2 hours. It was not rolling boil but measuring temperature, it stayed right around 200° with the lid on. This made no difference in the blank’s ability to bend. Do I need more time, more heat, green wood? Any comments?
Thanks,
Deke
Replies
Hi Deke,
I haven't tried that approach, but have had success bending both walnut and cherry that is kiln dried (I'm trying to figure out how to access green lumber in my area). I made a curb of 2x4 lumber lined with garbage bags, filled with water and weighted down the wood for a day or two before putting in the steambox, and steamed it for a long time. It was enough to make the gentle bend for a crest (top) rail of a chair. I can't recall the thickness, but it was at least 9/16"
I think Pete Galbert has published some on bending kiln dried wood as well.
https://www.youtube.com/watch?v=mkR3eBBYXB0
All the Wood we used for steam bending of chair backs was air dried.
I have bent kiln dried 6/4 cherry successfully. The cut is gonna be a big factor. Any runout is gonna split out. Soaking the wood for week or so will greatly increase your success rate.
Ok, I will try soaking. I am only bending 9/16" thick material. There isn't any runout. I am trying to bend in tangential direction. I have only boiled 2 hours but I'm not sure even where to start. Cracking is not an issue yet because I have been able to bend at all yet!
So, I guess a steam box is how I should approach this? Again, any ideas about time? Should I just keep checking?
Thanks!
Could you describe the method and equipment you used to attempt the bending?
It takes a lot of force to bend formerly dried wood after steaming/boiling it. The thicker the wood and the greater the required bend, the more will be the required force. Above a certain thickness it becomes unfeasible.
The amount you can bend a piece without it cracking or otherwise failing to remain undamaged will vary also with the species and the grain orientation within the piece. Pieces with grain directions that don't all religiously follow the bend will be more inclined to see cracks or splits.
To bend a steamed/boiled piece well you generally also need a two-sided clamp/caul that clasps the piece across its whole section, both sides, to provide the required shaping but also to restrain the piece from disintegrating. Bending without such containing restraints is more likely to see cracking or other failures.
Kiln dried wood doesn't bend nicely. It has been slightly chemically changed and no amount of presoaking or steaming will change this back.
2 hours is OVERKILL. Time required: 1" per hour of steam. But oversteaming is not a problem (unless it is days of oversteaming, not hours).
Grain direction is everything. Grain needs to be straight in both WIDTH and THICKNESS. It will blow out if not.
Wood on the tension side is at the higher risk to blow out, so that is where you need to watch. Don't bend anything much wider than 1" as this results in too much force on the tension side and it will blow out rather than bend.
After removing from steam, you have 30 seconds. Move with purpose and if longer than 30 seconds, abandon the attempt.
What wood species? Only hardwoods bend so don't try pine or fir or spruce. Oak is great. Hickory and ash too. I have heard beech is good, but never tried. No clue on maple. Cherry probably is good because it does everything well, or so it seems.
Do yourself a favor and start your bending adventures with:
1. Air dried white oak that you pre-soak for a week,
2. that is dead straight grain in both directions
3. 3/4" or less thickness on the bend dimension,
4. Gentle, one direction bend (no continuous arm bows on your first attempt).
Or better yet, get green wood, a drawknife and get those perfect grain fibers all intact. It is amazing how strong the resulting wood will be. 5/16" oak spindle that you can't break with your arms.
I'm currently working with green logs of white oak with grain as dead straight as a Starrett spirit level over entire 60" run. It was easy to split, then rive. It then peels back like butter with drawknife, producing amazingly perfect the arm bows. These for continuous-arm Windsors and they are bending perfectly without a strain of blowout.
The bendability of different species also depends on the length of the fibers in the wood. Ash, oak, and hickory all have long fibers; cherry has short fibers. It has more tendency to just break across it rather than have long splits on the outside surface of the bend.
Steaming is definitely more effective than just soaking or simmering. It takes more heat to soften the structure of the wood enough for easy bending. Kiln drying does change the nature of the wood, but it just makes it more difficult, not impossible. And, I've steamed and bent softwood lumberyard trim for curved walls, so softwoods can also be steam-bent. Good luck!
Lost Art Press had blogged about a product called “cold bend hardwood” that easily bends. If you poke around you could find those blog posts. I did find a YouTube video. Might get you more quickly to the end product with less experimentation.
https://youtu.be/FYh40UznTHM?si=U1G_BKNdvwD8kmRi
This is fascinating. I wonder how much structural integrity you lose with this product? it would be fun to experiment to see if it is brittle after drying, or if shear stress is compromised? Certainly for decorative purposes, it looks like a game changer. If I were making lighting fixtures for large restaurants, or other decorative architectural pieces, I would be investing in some of this. Thanks for sharing, Joe.
You are most welcome. Folks have helped me over the years. I’m happy when I can return the favor.
I too would like to try some bending. Where do you get green wood. Isn’t that really the challenge?
Got to get creative. Any log yards in your area? They will sell you one. Or friends/neighbors with trees recently fallen and/or in need to felling? Make sure these logs are the type that will nicely bend (oak, ash, hickory, etc) and are free of knots and generally straight grain to begin with.
There is a lot more to bending then green wood however. The key thing is the grain direction. If you don't know how to produce straight grain stock, you need to start there. Splitting, riving, drawknife...
But boy it is cool and amazing property of some types of wood.
😊
You guys inspired me. I contacted the superintendent at a golf course. We just had a winter storm. He said come over and peruse his collection of logs.