thompsondockside.com

Finely put together a steam box to attempt to bend some 5/8 x 1 1/8 air dried white oak. Used thinner can tapped with 3/4 inch conduit with gasket material and two nuts. Box is 1x10's. Drilled 1 inch hole and 3/4 inch pipe flange and short pipe attached to box. 1/2 inch dowel on 12 inch centers to support frames. Stuffed ends with insulation board.
Took about 10 minutes for box to heat up to 180 F after steam was produced. This was the highest temp I could get it. I had two frames in the box. Pulled the first one at approx 45 minutes. Bent it around the rung of a ladder. It cracked. It also separated where the grain ran out on one end. Second frame came out at 60 min. Bent it around a propane tank. It worked other than a couple splinters popping on the outer edge.

Thoughts:
The bend at the transom and 4 plus frames forward is extreme. I will likely build these.
I need to reduce the volume in the box.
Frames were not as pliable as I thought they would be. I may need to get the temp. up in the box by increasing volume of steam or insulating. Most likely more volume. I understand that the steam needs to "flow". Possibly larger volume and vents in box in bottom at each end?
Your thoughts?

You may want to contact one of the members that goes by treelineIII. His name is Eric. We got together and discussed these bending methods. I remember him telling me there is a very specific temp. that you want to hit. too cold or too hot will not give you the desired results. If you can't reach him through the site i will contact him and have him give you a shout...Dan

I'm no expert on this bending stuff, but I know that the bend is acomplished thru compression of the wood fibers on the inside of the curve. For extreme bends use a steel strap clamped to the ends of the outside of the stock, this forces the neutral axis outword giving more compression on the inside and less tension on the outside fibers... therefore less tendency to fracture the wood. A length of steel banding strap should work OK for this.
Joe B

One thing I noticed right away was that your steam supply hose looks a little small. A bigger hose (1 1/2 - 2") will get more steam into the box to get it up to temp. (212 deg).
Another thing that may help you is not to seal the box up too tightly. Steam should flow, as you said. Try leaving one end open for loading and unloading. Stuff a rag in there tight enough to keep the heat in, but loose enough to let some steam escape. It keeps the steam moving so it exits before it has a chance to cool, keeping the box at a consistent temp.

Thanx for reply. I have read about moving the axis out by use of additional material. My issue here is that my boat is upside down with garboards off and will be feeding the frames in from the keelson to the deck.

I plan on using the hull to shape the new frames. I may leave the old ones in place and feed the replacements along side, then slide them over when removing the old. Feedback on this process is appreciated.

Don Danenberg shows a 3/4 inch pipe on his steaming unit with a radiator hose. I will try increasing my outlet to 1 inch min. and make it larger at the box. He also states that the temp should be as close to 212 before loading material. I need to get the temp up definitely.

I guess I'll buy a section of radiator hose to start assembling a new hose line.

Questions/Feedback:
Best process for installing frames in my situation? Should I remove the decks?
How to reduce volume of box without rebuilding? Bricks or billet of insulation?
How many frames to steam at one time? I'm thinking twice as many as I think I'll be using per session. If this is the case I may need the entire box volume for the "real" job, but not for my trials.

"Woody to TreelineIII...Woody to TreelineIII...are you out there?" Can someone help me get TreelineIII on the line?
Thanx

Well Happy New Year to you all. I have not been checking the sight lately since I am not currently working on the boat. I actually am building a ceder strip kayak at the moment. But enought about me. Dan good to hear your voice, sorry we have not connected. Maybe this new year will find us out on the boats at the same time.
Let me see if I can share some thoughts on the steam bending. Everyone seems to have a different approach, and each one may work for one and not the other. Here is what worked for me. Sorry no pics to add.
First off 212 is the target. Period. This is critical.
I built the box out of a large PVC pipe and used 2 of my camping burners to double feed the steam in. one at the end and the other about half way through. You can buy end caps that you can put on. I set the pipe on a slight angle and cut a hole on the bottom of the low side to let the water drip out. I also drilled holes across the middle every two feet and then slid wood dowel across. This way the rib was suspended in air and not sitting on the bottom of the tube in the water. I think this helped to make the hot steam circulate around the rib better.I can not remember exactly how long I steamed it, but I seem to think it was 30min. I did two at once.
It is very helpful to have help when you pull the rib out. I bent the rib directly in the boat. If you steam it right they comeout like noodles. I forced them direcly in place behind the frames in the boat. It helps to have one person pushing it down in, and the other guiding the front edge over the lap edges. The rib tends to get jammed and it helps to have a person kind of lift the front edge so it can continue to slide in. You need to work fast because the rib does cool pretty quick. Keep in mind, on my boat I was replacing about 6 ribs and did not have the laps taken off so I had to bend them directly on the boat.
I presume you are using the white oak with proper grain. If you see the grain run out on the edge it is a good chance that is where it will brake.
Not sure what else I can share on this, but I wish you well. I have to say when you get it, it is really cool. To be able to bend wood like that is really fun. I will be checking more regularly on this post to see if there are other fun project going on. For now I am trying to figure out ceder stip building. Another challenge on it's own right.
Eric

I was just rereading some of the other comments. I forgot to comment that the steam tube I used was 1 1/2". I also had a small hole on top to at the high end of the tilted PVC. This allowed the steam to flow through. Not too big though you want to keep as much steam in and yet let the air flow.
If I think of more I will repost.
Eric

Eric
By your description I need more heat. No "noodles" during my initial trial.
Thanx for your feedback.
Woody (Larry)
side note:
I built a cedar strip canoe about 6 years ago. Rewarding project. A friend and I took on the project. Four hands are better than two.