PDA

View Full Version : Wet bending



tink
05-30-2015, 11:54 AM
I need to bend the gunwales of my 12x30 canoe. I have some nice clean pine 1 inch x 3/8 inch. It takes the bend relatively easily but also has to twist about thirty degrees. I don't really want to go the the whole steam box route. I listened to a podcast in which someone just soaked the wood in water.

Has as anyone used this technique?
How long would I need to soak it for?
Are there any downsides?

Here are the lines so you can appreciate the bending

https://tinkboats.files.wordpress.com/2015/04/img_2495.jpg

Tink

Peerie Maa
05-30-2015, 12:13 PM
The Shetland boat builders soaked their 2 1/2 by 1 3/4 gunwales for a week. They were then pre-bent off the boat overnight before being fitted. I don't know about putting in a twist, as the Shetland boats did not tumble home like your canoe.

upchurchmr
05-30-2015, 12:43 PM
Have you tried just a heat gun?
Your gunwale size is thicker than a typical strip planked canoe or kayak, but I bend 3/4 x 1/4 with a relatively small application of a heat gun.
Just determine where you want the twist and estimate how much. Clamp the stock down with a free end sticking out.
Grab the end with a cresent wrench, applying a bit of twist, heat the free length of board with the heat gun (on hi - 1500 degree setting) keeping the heat moving slowly. Heat both sides.
With a little practice you can tell when the board is hot enough, the force to twist the board gets less as the fibers slip.
Quit heating while holding the twist until it cools off. How long is an experiment, but the best thing is you can keep doing this in steps until you get what you want.

If you overbend it you can just reheat and bend it back.

Works like a charm and you can immediatly use the board, unlike with steam or water.

Probably take 5 minutes total (after you experiment a little).

If you stop moving the heat you may toast (burn) the surface, but it is usually removed with a minimum of sandpaper work.

Peerie Maa
05-30-2015, 01:40 PM
Another way is rags and kettles of boiling water.

pcford
05-30-2015, 01:40 PM
Steam bending is no big deal, especially with small sticks like this:
1. Get 4" drain pipe of the appropriate length. Caps for ends.
2. Rent wallpaper steamer.
3. Bore holes for steamer hose and one for drain.
4. Steam one hour for inch of thickness.

hokiefan
05-30-2015, 02:09 PM
My bet is you don't need anything to make that bend. Clamp it in the middle and bend it. I would certainly try that first.

Cheers,

Bobby

Hunky Dory
05-30-2015, 02:32 PM
I just did what PC Ford said. 4" drain pipe 9.95 for a 10 ft. lenth. I borrowed a wallpaper steamer and capped the higher end with a plastic deli container and put the steam hose in the other end with rags stuffed in around it . The condensate drained out next to the hose and I got it up to 210 degrees according to mommas meat thermometer stuck into the deli container. I had to wrap some towels around the pipe for it to get that hot as the pipe looses heat.

ssvmi91
05-30-2015, 03:12 PM
I tried loosely wrapping boat ribs in 6 mil plastic and hooking it up right to the steamer. It worked great, basically cooked the wood and allowed me to bend it with a bar clamp. This is the video where I got the idea:

https://www.youtube.com/watch?v=--iPQIwSEJM&list=PLzlN3A2DLgNwTtCNg1R3fmjiDkulWoNXa

My only improvement recommendation would be to wrap the wood in a wet towel and then plastic overnight before you put the steamer to use

Steve

pcford
05-30-2015, 03:18 PM
I tried loosely wrapping boat ribs in 6 mil plastic and hooking it up right to the steamer. It worked great, basically cooked the wood and allowed me to bend it with a bar clamp. This is the video where I got the idea:

https://www.youtube.com/watch?v=--iPQIwSEJM&list=PLzlN3A2DLgNwTtCNg1R3fmjiDkulWoNXa

My only improvement recommendation would be to wrap the wood in a wet towel and then plastic overnight before you put the steamer to use

Steve
Yes. Soaking overnight can not hurt. It seems to lessen the chances of busting. The moral to the story is that steaming is easy.

sheerline
05-30-2015, 03:26 PM
That stock will go on without wetting or steam. Start fitting at the end with the most twist an work your way round, fixing as you go.

Trev

Gib Etheridge
05-30-2015, 03:44 PM
3/8" by 1"? Just clamp it on, no heat required.

A couple of days in a local pond will help, if you insist. I just soaked some very dry AYC, 3/8" by 4" by 6' for two days before steaming and bending to a 19" radius for cowlings. The soaking was the only thing that made it possible, the YC was that dry, but soaking made it easy. I remember a forumite who insisted that moisture content doesn't matter. Wrong, wrong, wrong.

If you go with steaming in a pipe use the smallest diameter pipe that the work will fit in and wrap the pipe in old blankeys or pipe insulation.

Seagull_Sid
05-30-2015, 03:47 PM
I believe the piece will bend in with no steaming also but it really depends on how stiff that piece feels when you're trying to work it. I've also used a chunk of drain pipe but with no steam at all. Just cap one end pour in 2-4 cups of water, lay it out in the sun with the open end slightly up so the water won't run out and stuff a rag in the opening. After a few hours in the sun the piece seems to become much more co-operative.

If you're not in a big hurry you can just bend it as close as possible dry and leave it under tension outside overnight, increase the tension a bit the next day and repeat until you have the shape you want. The upside is that by the time I want coffee the sun has hit the piece and it's dry enough to glue and finish.

upchurchmr
05-30-2015, 04:35 PM
I can't believe most of these suggestions talk about 1 day to weeks of preparation.

Are you people serious?

Try it without anything. If you break it, then try the heat gun with a new piece of wood.

Of course you could also set up an anhydrous ammonia "steaming" system. It is just a toxic poison requiring lots of equipment. Or you could go get the bendable wood from the guy who puts the wood in a hydraulic press for days or weeks. :rolleyes: Another suggestion is to cut it into 1/8" plies and laminate it on the boat. Don't forget to put a separator on the boat so you can get it off to clean up the edges. I probably can think of other hard but cool ways to make this.

Why make this harder than it needs to be?

pcford
05-30-2015, 05:01 PM
Yes I would think that this would bend in easily...but the OP is there and he is concerned about the twist...

tink
05-31-2015, 01:27 AM
Big thanks for all you replies and the healthy discussion. The bend is not much of an issue it is the twist that the wood is not liking. I will try Slug's suggestion of the wet blanket in the black bags and cook in the sun. I have all the gear a need for that lying about and it seams easy.
I will let you know how I get on,

Thanks again on and all

Tink

sheerline
05-31-2015, 07:55 AM
A good splosh of parrafin/kerosene will ease the process.
I made a portable steamer from an old expresso machine that feeds the steam into a heavy polythene flexible tube. Slide it on seal it and steam away. Works great for getting those twisting hood ends into place.

Trev

Tom Lathrop
05-31-2015, 08:08 AM
Like others, I have bent on outwhales like that with twist and bend without wetting but some soaking will make it easier and more trouble free. Pine can be more brittle than other woods so that can be an issue. One thing that is good practice in bending on any wood is to fix the end with the greatest bend first. This allows using the longer part as a lever and makes fairing the piece in better.

sailcanoefan
05-31-2015, 08:19 AM
For my 19 ft sailboat, I soaked 3/8 inch plywood for 24 hours. Parts designed to be fixed around the stem were impossible to bend, instead they would have broken. After soaking they were more flexible; gradually on a period of 2 hours, giving more tension each 1/2 hour, the bend was ok. I temporary screew plywood for 24 hours to led dry the plywood. Next days, after removing screews, plywood remain bent and was ready to permanent fix. Do the same for gunnells and other parts to be bent. Soak, install wet, let dry, then fix permanently (glue and screews)

sailcanoefan
05-31-2015, 08:21 AM
One thing that is good practice in bending on any wood is to fix the end with the greatest bend first. This allows using the longer part as a lever and makes fairing the piece in better.

I agree !!!

seo
05-31-2015, 11:44 AM
I've noticed that sometimes you can bend a piece of wood to the curve and twist that you want without steaming, but then the piece will split, sometimes when fastening, sometimes after all is said and done.
My understanding of it is that wood fibers are bound together with a natural "glue," and that heating the piece relaxes the "glue" so that the fibers can slide by each other as the piece is bent, and then when the piece cools the "glue" sets again. This relieves the internal stress in the workpiece that you get when you bend it dry.
I also think that wood that is green from the sawmill bends very easily. I've bent 1/2" X 2" white oak to surprisingly small radius without steaming, but that was very green stuff. Steamed, you could just about tie it in a knot. While just about any wood can be steam bent, I think green wood bends most easily, air dried next best, kiln dried least well. That said, I have steam bent kiln dried cherry and black walnut for the back pieces in a ladder-back Shaker chair, and they truly bent, in that when released from the bending form they didn't spring back straight again.
I've had good luck making a steam box out of "blue board" rigid insulation, using the kind of bamboo skewers that are used in Thai cooking for "nails" to hold the pieces in alignment, and some ductape to hold them together. Regular nails would have worked as well... Plastic downspout also works for small dimension pieces.

Some people say that steaming the wood lowers the moisture content after the wood has cooled, and that the heat kills rot spores in the wood. I've also heard that overheating the wood will make it stiff and weak, and maybe that's a reason to use the naturally regulated temperature of wet t steam instead of a heat gun. That said, I was once involved in replacing a garboard plank on a big powerboat that took an almost 90 twist before landing on the stem rabbet. The plank was 20' X 2" X 12" old-growth yellow pine. The guy calling the shots had a plumber's torch, the kind that connects to a 20 Lbs. propane bottle, and shrieks like a damned soul. The piece bent in very nicely!
One thing that experience brings is a sense for when a piece of wood is nearing its breaking point.

spirit
06-01-2015, 11:58 AM
Simple: steam bend the rails in place in plastic tubes.
See: https://www.youtube.com/watch?v=--iPQIwSEJM&feature=youtu.be

paxtonm
06-01-2015, 12:23 PM
Wet rags and an electric iron will also produce some flexibility.

tprice
06-01-2015, 12:25 PM
I think his real issue is with the edge set necessary to follow the sheer when the fairly extreme tumblehome is introduced. Wrapping around the tumblehome gives the piece a "frown" while a "smile" is necessary to bend along the sheer. At 1", even that thin strip is fighting him, dry. Soaking, then heat gun seems like it would do the trick. Clamp on to pre twist then remove and fasten when dry.

tink
06-06-2015, 01:48 PM
Progress, have finished taping the seams and ready for the gunwales. Have scarfed two lengths of pine together and with a good hot window coming up going to 'solar steam' over the next few days. Will also be buying a few more clamps.

Tink

upchurchmr
06-06-2015, 02:50 PM
What kind of glue did you use for the scarf?

Almost nothing works well at higher temperatures like "steaming".

Hope it doesn't come apart when you do the bending.

Peerie Maa
06-06-2015, 02:55 PM
Progress, have finished taping the seams and ready for the gunwales. Have scarfed two lengths of pine together and with a good hot window coming up going to 'solar steam' over the next few days. Will also be buying a few more clamps.

Tink

Steam the ends to put the twist in off the boat. Do not heat near the glue. Then when the ends are twisted, wrap the timber around the boat cold, do it in easy stages and you should be OK.

tink
06-06-2015, 03:36 PM
What kind of glue did you use for the scarf?

Almost nothing works well at higher temperatures like "steaming".

Hope it doesn't come apart when you do the bending.

I just used Gorilla glue, something I may live to regret- life is nothing if not an experiment. There as a post by Slug suggesting a wet blanket in the black bags and cook in the sun. I have all the gear a need for that lying about and it seams easy so I was going to try this method. (I can't find Slug's post now?) I am hoping this make the wood green enough to bend without getting too hot.

Thanks

Tink

tink
06-06-2015, 03:46 PM
Steam the ends to put the twist in off the boat. Do not heat near the glue. Then when the ends are twisted, wrap the timber around the boat cold, do it in easy stages and you should be OK.

thanks for the advice Nick, any advice on the best way to apply twist off the boat?

Thanks

Tink

upchurchmr
06-06-2015, 05:16 PM
Gorilla glue sucks.
Good that you are listening to Peerie Maa.

If you were just doing it with a heat gun I would say use a crescent wrench to apply the twist, then hold it while it cools a few minutes.

Since you are soaking the wood I don't know how long you need to hold it.

Peerie Maa
06-06-2015, 05:26 PM
thanks for the advice Nick, any advice on the best way to apply twist off the boat?

Thanks

Tink

Clamp the middle foot or so down to a bench or a strong bat of wood up to where the twist begins. The bench or bat of wood needs to be just shorter than your gunwale, or do one end at a time if you have not a long enough bench. Then make a spanner or use a clamp to grip the end as suggested by upchurchmr. When softened and pliable use string from the end of the spanner or clamp to a peg in the ground or some other fixed point to hold the twist in whilst the wood cools and sets. Put a bit of over twist in, so that you can adjust it on the boat.

Woxbox
06-06-2015, 08:22 PM
I"m with the heat gun crowd. Start clamping it in place. If it won't bend somewhere along the line, hit it with the heat gun and it will go readily. No water, no steam needed.

tink
06-07-2015, 03:03 AM
Clamp the middle foot or so down to a bench or a strong bat of wood up to where the twist begins. The bench or bat of wood needs to be just shorter than your gunwale, or do one end at a time if you have not a long enough bench. Then make a spanner or use a clamp to grip the end as suggested by upchurchmr. When softened and pliable use string from the end of the spanner or clamp to a peg in the ground or some other fixed point to hold the twist in whilst the wood cools and sets. Put a bit of over twist in, so that you can adjust it on the boat.

Thanks Nick that makes sense, with the facilities I have that would require me to make a quite elaborate jig. If the wood is flexible enough what are the down sides of bending in place. I would do both sides at the same time so shouldn't distort the hull which is the only issue I can think of.

Thanks Tink

Peerie Maa
06-07-2015, 03:32 AM
Thanks Nick that makes sense, with the facilities I have that would require me to make a quite elaborate jig. If the wood is flexible enough what are the down sides of bending in place. I would do both sides at the same time so shouldn't distort the hull which is the only issue I can think of.

Thanks Tink

Make sure that all of your clamps are to hand and enlist some helpers as you have to work very quickly. Do not worry if the gunwale does not follow the sheer exactly as you can make minor adjustments later. Leave over long so that you have something to grab and apply the twist.

tink
06-07-2015, 10:36 AM
Make sure that all of your clamps are to hand and enlist some helpers as you have to work very quickly. Do not worry if the gunwale does not follow the sheer exactly as you can make minor adjustments later. Leave over long so that you have something to grab and apply the twist.

Thanks Nick
will certainly follow your advice, have more camps on order and in the mean while I am cooking the wood wrapped in wet rags and sealed in bin bags. They are in quite a sun trap. I tried the bend the now scarfed lengths but they did not quite make it. I will report on how effective this method has been.

for pics see https://tinkboats.wordpress.com

tink
06-10-2015, 01:36 PM
https://tinkboats.files.wordpress.com/2015/06/image12.jpg
Got impatient, it has be a very hot day and I have regatta coming up and there was a window to try fitting the gunwales. The extra clamps have not arrived but I figure I can add these later and pull the gunwales into place a little more later. It was evening when I fitted them so they where cool but smelt of wet wood. The wood did bend into place quite easily and I think the wetting and solar heating had an effect though to be honest it was not a massive.

tapsnap
06-10-2015, 05:37 PM
Pine doesn't respond well to steam bending - steaming and heating will have little effect. You were right to do it without heat. The Gunwales on fearings bend in without heat and the tension on those are far greater.

tink
06-11-2015, 12:48 AM
The Gunwales on fearings bend in without heat and the tension on those are far greater.
The bending was not an issue, it was the twist of the tumble home that was hard. Anyway this morning all is well, no cracks and when I remove the odd clam the wood stays where it was.

Tink