Steam-bending wood

How we got into steam bending

There is no steaming envisioned in our purchased plans. But we simply could not put stringers on our boat without cracking them, be it kiln dried fragile “supermall” timber or the better naturally dried lumbermill timber. We suspect it has to do with our added transom and thus a more complicated geometry.

Heating not only allowes you to bend wood like a bow, but also give the wood a torsion bend. This is highly impractical without steaming, as experience thaught us. What is more – the wood will hold it’s bend after releasing off the form. Of course, there is some springback, but that can be concidered for.

The PVC pipe design

The most common DIY steam bending solution you’ll find on the net is the PVC pipe housing plus some sort of source of steam.

Getting the pipe is rather straightforward – buy the necessary length of PVC pipe (with the diameter you need) that can stand up to 100 C temperature. Factories usually print this data on their pipes, but when in doubt, ask the salesman. You ought to buy at least one endcap to the pipe for fitting the inlet hose. The other end can simply be covered with a cloth.

Source of steam

This is where the DIY steam bending culture varies. Some use a tea kettle heated by a stove, some use a rebuilt metal gas canister heated by the good-ol campfire, some use rocket fuel.. We decided to try something that we had not seen before – two instant 1 L water boilers.

This choise was made because it seemed (and perhaps still seems) the simplest and best applied in an indoors environment. We can not make an open fire indoors, nor have we a proper stove. So we chose the mentioned kettles.

To use the kettles, one must remove the auto-switches to allowe for “infinite” boiling. Though care must be taken not to burn the kettle once the water runs out. You need water, it will keep the system at a constant 100 C. Otherwise – Tšernobyl.

A word on heat and plastic

Whatever plastic you use, be it the hose, PVC pipe, kettles or silicone sealant – make sure it can tolerate excess of 100 C, the boiling point of water. Otherwise bad things will happen fast:

  • The steam hose can collapse on itself, causing overpressure in the kettle and in worst case causing an explosion.
  • The PVC tubing can collapse on itself, rendering it usable only once.
  • The silicone can simply yield and thus rendering the system usable only once.

A word on efficiency

Whatever the source of steam, covering your PVC pipe with old blankets will vastly improve the setup. The steam will be hotter, the pipe will actually get hot enough to pass steam (not only condensate) and the whole thing will happen faster.

Pictures, pictures, pictures!

Right, enough “discussion”, lets have it:

 

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