A Small Stem Bending Machine
Here is our steam bending machine based on a design for a much larger version I plan to make in the future. The jig was cut on a CNC router.
The timber in this example is 66x19 Maple Silkwood with a colonial molding shaped on the top.
The radius is 270mm
We Provide Steam Bending or Laminating Timber Services.
The Pros and Cons of Steam Bending:-
Steam Bending Timber.
With Steam Bending Timber the timber is placed in a sealed container or box and steam is introduced via a pipe from a boiler. As a general rule we allow about one hour for every 25mm or 1″ of thickness of timber. This varies depending on factors such as the age of the timber, species and severity of the curve to name a few.
Once heated, the timber is then bent around a specially designed form to the desired shape.
We are currently in the process of designing and building a large forming machine which will help to speed up the process and produce consistent results.
We will also be re-branding this section of our business to Dragon Breath Stem Bending.
Advantages and Limits to Steam Bending Timber
- Steam Bending is fast as it does not require a lot of cleaning up after the bending. However bear in mind that for just about any steam bending job a form is required to bend the timber around.
- Some discolouration may occur which needs to be sanded out
- If the bent timber is not being used straight away it needs to be held in place mechanically to overcome any problem with spring-back
- Sometimes, timber size and the radius you are bending around are simply not possible and are considered on a job by job basis. In this case a combination of steam bending and laminating is an option.
Laminating is achieved by cutting the timber into narrow strips and then glueing together around a form or jig. This creates a very strong and permanent shape. It also allows very large cross sections to be made which would be too large to steam bend.
The down side of laminating timber is that it is a slow process. there is a lot of machining of the timber. Once the glue has set and the shape formed, more labour is required to shape the desired profile.
STEAM BENDING TIMBER IN A BOAT YARD
And now, to incorporate the skills I learned in Boat Building into my everyday Joinery and Cabinet Making projects.
WOODEN SHIPS BUILT BY IRON MEN
Firstly, let me define a ship. The definition I have always liked is a ship is any vessel that cannot be lifted onto the deck of another vessel. So in days gone by, even Captains Cook’s Endeavour would have been considered a ship. Hence the heading.
As an introduction, I did my apprenticeship in Brisbane in a traditional timber boat yard building working on pleasure and work boats to 100’ in length. A mixture of sharpies (hard chine) and carvels (round bilge). Steam bending was a way of life.
One of my greatest regrets was that I never took photos or movies of the process. Even if I had wanted to, the boat yard was run with such a firm hand that it would have been impossible. Dirt floors, Personal Protective Equipment (PPE) was a dirty word. If guys wore them at all, the chosen footwear was Dunlop Volleys; or thongs. Music or a radio playing would have meant instant dismissal, and you never stopped to have a chat with someone. This would have brought down the foreman and one of the owners upon you for a half hour lecture on time wasting. Kind of ironic really.
If you were to look up “Dickensian” in the dictionary I am sure it would say “refer boat yard”
I don’t consider myself to be the world’s best boat builder, or even close, however I won awards for it and remember nearly every minute vividly. I can also still name every part of a traditional timber boat without having to think. So I have decided the next best thing to images is to pass on my experiences here in the 10 years I worked as a boat builder.
I have noted on one of the woodworking forums that there is interest in bending timber. Of course, a big part of boat building.
The Art of Steam Bending Timber in Boat Yards Has Been Refined Over Hundreds of Years.
We had to do large quantities in a short period so the gentlemanly method of steaming was not really an option. Instead we had two 12” dia old steel chimneys about 20′ long. They were sealed at one end to make the water tight. The other end was perched on a steel “A” frame to incline the two pipes at an angle of about 30deg.
You can imagine, building timber boats sometimes three at a time, out of almost exclusively hardwood, there was any quantity of off cuts. These were stockpiled to provide fuel for boiling the pots. This pile grew to about the size of a car and was handy to the pots next the jetty slipway and the jetty. The pile diminished greatly once timbering started. Depending on the size of the boat, timbering (or ribs) involved bending three laminations of 3’’ to 4’’ dressed hardwood from the keel to the sheer clamp. The timber was dressed on the face only as this reduced the incidence of the outside lamination splitting.
By the way, the three pieces were bent together using a double sheave rope block and tackle at the top and very large G clamps; up to 36”. The timbers were locked in behind the garboard plank (the first plank beside the keel) and then slowly bent around the hull. At first with the clamps, and then, as they were bent higher up the side of the hull, assisted with the block and tackle.
Generally the timbering started from amidships. This allowed four gangs or three of four men to work. Two gangs towards the bow and two to the stern. Two teams on either side of the boat.
A team could bend and nail off a set of timbers in about 30-45 minuted and when one set was in place they would shout “timbers” and the apprentices manning the pots would run another set.
It was the job of the two apprentices to keep the fire going, and when one pot ran out fill it with more timber and of course, run the timbers to the teams.
The conditions like most things in the yard were pretty basic. Boiling black water would slosh out of the ends of the pipes occasionally so you had to be on your toes to avoid it. You did get some warning as things would start to gurgle and a huge bubble would come up from the bottom of the pot. This is what forced the water out. From my high school chemistry days, this is referred to as bumping.
The timber was carried up the shed with the aid of hessian bags. This is what kept the apprentices from burning their hand on the red hot timber. By the end of the day however you were black from the water that dribbled down your arms and, exhausted.
Bear in mind also that depending on the boat being built, this process repeated itself for days if not weeks.
The largest pieces of timber I was ever involved in bending were two pieces of spotted gum 14”x4”. The top clamps of an 80’ boat destined for Melbourne. A top clam is the piece of timber that runs from bow to stern at the deckline. All pieces below are stringers.
This was not bent institute because of the weight and force required. It was also shaped toward the forward end to reduce the resistance.
Instead, of trying to bend it in place, 12”x12” hardwood blocks were set up vertically at various distances apart on the shed floor to replicate the shape required. Bent and left for a few days to “set”.
I have given all dimension in imperial simply because that is what I remember. I will leave it to you to convert if you are interested.
Please feel free to contact me if you would like more information or stories on boat building.