steam bending oak frames

[ossygobbin]

hi,
have any members experience of steam bending oak frames? i have to replace a number of oak frames on the kestrel 22 i am restoring and i am undecided how best to go about this because, at the widest point of the hull the frames themselves are one piece, (that is continuous down the sides of the hull over the keelson and up the other side.) passing under the stringers on both sides. is it possible to steam bend and fit this length of timber frame? bearing in mind that on fitting, you will have to fiddle about sliding it down the back of the stringers, and then have to physically rivet it in place. is there time to do this? or will the frame become unworkable before i am able to get the fasteners in? all advice r/e steam bending and fastening will be gratefully received. cheers ian

<hr width=100% size=1>

 

[tillergirl]

I've done a similar threading of a new frame behind a stringer but only half what you have to do ie I only did one side as the frames are not continuous over the keel. Tiller Girl is 32 foot so the frames are larger in section than your Kestrel. You will be surprised at the flexibility you can get but you will have to work very quickly to thread it through both sides - I guess its quite a long frame as well which will need a long steam pipe. We used a wallpaper steamer as a generator of steam and lagged the far end as best we good to keep up the heat at the other end to the feed.

I would say crucial thing is to get the steaming operation as close as possible to the fitting site; clear the fitting area - you really do need the best access you can get, be ready to handle very hot timber - you won't be able to dawdle, and be prepared to give it a bit of pressure - there will be initial resistence to bend but then it will go. Get really good quality oak, blemish free, champer the inside edges to relieve compression tension, be prepared for a couple to snap as you put them in but don't worry about the fastening bit, you'll have plenty of time for that, steam it, bend and insert it into place and it will stay there ready for you to fasten at a slower pace.

It's very satisfying work.

<hr width=100% size=1>

 

[Peterduck]

The other consideration is that when you are selecting the timber for steam-bent ribs, it is crucial that the grain run along the rib all the way. I believe that ribs used to be split from the main baulk of timber to ensure that the grain was follwed all the way. If the grain runs out to one side at all, that is where the rib will fail first.
Peter.

<hr width=100% size=1>

 

[calloo]

I concur entirely with the previous contributions. I have a little experience of this and suggest that the quality of the oak is most important. Last time I did this I used Japanese oak which when steamed was very pliable. The period spent steaming is also vital. I rigged up an old tea boiler which held a couple of gallons and allowed the steam to pass unimpeded into the pipe. The pipe I used was an old cast iron pipe I got from a scrap yard. Cast iron is good for containing heat. You have to be quick. Have everything prepared and if you cock it up don't waste time trying to recover a bad job. Start again. Good luck

<hr width=100% size=1>

 

[mikesharp]

I have seen an article which described steaming timber inside a plastic bag and the bag kept on until the timber was bent into place (including fastening) I think it was on the Wooden Boat website.

<hr width=100% size=1>

 

[robind]

I would reccomend that the tube, whatever it is decided upon is lagged with old insulation/blankets whatever is available so that the heat and moisture has a chance to work the timber. What is the cross sectional size of the rib/s to be bent.
Rob.

<hr width=100% size=1>

 

[ossygobbin]

hi,
the cross section of the old cracked frames is about 1 1/2 x 3/4 inch. what worries me is trying to get the complete length of timber behind both stringers over the keelson etc.

cheers ian

<hr width=100% size=1>

 

[Spuddy]

If you work it out, let us know. It's one of those headscratchers.
I picked up a tip of an hour steaming for every inch of thickness. Too long and it do take the nature out of it.
regards...spuddy

<hr width=100% size=1>

 

[daveyjones]

Have you considered laminating frames rather than steaming? Much easier to bend thin strips into position, and it should be stronger than the steamed version. If the interior is painted, you wouldn't know the difference anyway, but personally I think laminations look pretty!