Binman
Well-Known Member
Have a look on utube, blokes doing a long piece in a polythene bag, very easy, I would try that route if I ever needed to.
Bendy timber for gunnels.
- Thread starter burgundyben
- Start date
JumbleDuck
Well-Known Member
The point of steaming is simply to heat the wood, and in general diffusion times for heat (or anything else) follow a square rule: to penetrate twice as far takes four times as long.
KREW2
Well-Known Member
Just a short update on my previous post about replacing 2x1, 6ft length of iroko gunwale.
As I said, I steamed it for nearly two hours in a piece of pipe, it seemed to be working well as steam was gushing out of the hole drilled in the far end, even then when removed it was not that pliable. By the time I had finished clamping it into place (about twenty minutes) the wood had gone cold, nonetheless it was a good fit.
On Friday, after eight days in place I removed it in preparation for epoxying into place, whilst it had a bit of form it still needed a bit of coaxing to get it to bend on.
The job looks good, but I think we could have achieved the same result without steaming.
I would like to know if hard wood like Iroko or Teak would become more supple with a longer steaming time?
As I said, I steamed it for nearly two hours in a piece of pipe, it seemed to be working well as steam was gushing out of the hole drilled in the far end, even then when removed it was not that pliable. By the time I had finished clamping it into place (about twenty minutes) the wood had gone cold, nonetheless it was a good fit.
On Friday, after eight days in place I removed it in preparation for epoxying into place, whilst it had a bit of form it still needed a bit of coaxing to get it to bend on.
The job looks good, but I think we could have achieved the same result without steaming.
I would like to know if hard wood like Iroko or Teak would become more supple with a longer steaming time?
andygc
Well-Known Member
An hour for inch thick iroko should be sufficient. Longer won't help if you've had a good flow of steam and good insulation. The essential thing is the speed of working - you need to get the wood bent to shape as quickly as possible. For your job you would have been better to make a former (somebody suggested poles in the ground) so that you could have trapped one end and then bent the other end immediately to shape, worrying about intermediate clamps later. The wood will always spring back as it cools, so a bit of overbending on the former is a good idea.
JumbleDuck
Well-Known Member
Wood becomes pliable when it's heated to a temperature at which the xylem matrix becomes softened, allowing the cellulose fibres to slide through and locking them in place again when it cools down. From memory - necessary book 100 miles away - that happens at around 90oC, which is why steam is a convenient way of applying the heat. However, steam isn't much hotter than the required temperature, so a long soak probably won't do very much additional good as the xylem won't get much hotter (100oC max) and therefore won't get much softer.
You might be able to improve things with a pressure cooker: steaming at 5 bar would get the wood to around 150oC, but making the device would be a significant engineering undertaking with some fairly spectacular possibilities if it went wrong.
cliffordpope
Well-Known Member
Steam in a bag is the easy way.
You can buy rolls of polythene tube, or just use old lengths cut from sacks and staple them together.
Wrap it round the first 6 foot say of wood, and clamp one end into the final position. Pass in steam from a wallpaper steamer, stuff rags in the ends, and after a while see if it will bend. When it will, slide the tube along a bit and clamp the bent bit. Keep moving along until the whole section is bent, then fasten and remove the clamps.
Or, use tube over the whole length, bend into position and clamp, and then cut the polythene off.
No need for scalded fingers or rushing to position hot timber, just bend and clamp as you go.
You can buy rolls of polythene tube, or just use old lengths cut from sacks and staple them together.
Wrap it round the first 6 foot say of wood, and clamp one end into the final position. Pass in steam from a wallpaper steamer, stuff rags in the ends, and after a while see if it will bend. When it will, slide the tube along a bit and clamp the bent bit. Keep moving along until the whole section is bent, then fasten and remove the clamps.
Or, use tube over the whole length, bend into position and clamp, and then cut the polythene off.
No need for scalded fingers or rushing to position hot timber, just bend and clamp as you go.
pmagowan
Well-Known Member
I think the 20 minutes is where it went wrong. It takes a long time to heat the wood up but wet wood cools down fast. You should aim to have your bend within a minute or two of removing from the steamer. I found using a fence in the garden with an additional pole or two to be a useful frame to bend around. I was able to get it out of the steamer and into shape within about 30 seconds. The key is to have a couple of offset poles to catch one end. You jam that end in quickly and it is held in place for you to bend the rest around the jig. I use string to pull the free end in tight because it is adjustible and quick. To be honest with a convex hull shape to attach to you are better with a little less bend as it is easier to get it right adding the final bend as you fix it from one end to the other than trying to unbend it in place. It will lose some bend if you steam it again but it is hard to fit in the steamer once you have the bend on.
I like this idea of a bendy steamer made out of polythene bag so that you can bend the wood without it coming out of the steamer. I have seen this mentioned in books but I have never had the bag to hand when I have needed it and it has always been easier to knock up a steamer in a tube (we have plenty of these kicking around.) Anyway, glad you managed it. It is a bit of fun but it looks good when it is done.
KREW2
Well-Known Member
As I said it was not a vicious curve.
I realize now that trying to bend it through 3 dimensions on the boat when warm was not going to be easy in a short time frame.
pre bending as it came out of the steamer is obviously the right way to go, but this would have only given me a a curve from mid ships to bow. As the bow was some 4/5 inches higher it also needed to be bent upwards, and twisted through about 10 degrees to follow the line of the boat.
I hope the OP has gained as much info as I have from this thread.
I realize now that trying to bend it through 3 dimensions on the boat when warm was not going to be easy in a short time frame.
pre bending as it came out of the steamer is obviously the right way to go, but this would have only given me a a curve from mid ships to bow. As the bow was some 4/5 inches higher it also needed to be bent upwards, and twisted through about 10 degrees to follow the line of the boat.
I hope the OP has gained as much info as I have from this thread.
caiman
Well-Known Member
The two posts suggesting flexable polythene tube are the way to go.There have been two re gunneling jobs happening here recently.Mine on a Saltram 24 workboat(finished last week) around which the Iroko bent nicely cold,and an IP23 which needed the Iroko steaming to get around the stern.After starting with the drain pipe,the IP guy switched to poly tube and achieved much better results(at my suggestion I might add).The problem with the drain pipe method is that the work piece cools far too rapidly between the steamer and the hull,whereas using the poly tube the timber is still being steamed as it is worked around the hull hot.There are loads of vids on You Tube about it.
Hope this helps.
Cheers
Hope this helps.
Cheers