Steam Bending Experiment 2 – Success

I write this as I sip a beer in celebration.  My second steam box was a success, but only after some mid-steam additions.

I bought some flexible ducting from a reclamation yard for £10, strapped it down to a study stretcher and blanked off the ends.  I steamed a few strips of 2x1 pine and maple for an hour.  They had hardly become flexible at all and were not even that hot or moist to the touch.  I pondered and decided the steam was condensing back into water too quickly.  The heat and water was escaping from the steam box and not being forced into the wood.

So I improved the seal at the top end, shortened the hose and insulated the whole thing with multiple layers of cotton sheeting, blankets and reflective Mylar sheets.  After doing this the outside surface became only warm to the touch where it was previously untouchably hot, the trickle of water reduced to a drip and the small jet of steam escaping became more furious.  This all suggested that both the temperature and the pressure inside were rising. And it seemed to work because after 3 hours in the steam box I was able to bend my test piece.

All the steam-bending books recommend green wood but absolutely insist on knot-free, straight grain with no grain run-offs.  This 2x1 pine is about 2 years old so it's not particularly green.  It has paint on 2 sides but I chose it for it's straight grain and knot-free construction.  It was steaming for 3 hours but the first hour and a half  of that was without the improved insulation.  I reckon it would need less to do it again.  It took a fair amount of force to bend it into place and it looked, felt and sounded on the limit of breaking.

Note:  It was very hot to the touch which I think is a good guide for future bends.

This experiment was a test of the steam box not the jig but it is worth noting that I did not have enough clamp points along the curve.  I spaced them every 15 cms and as a result the arc is not perfect with visible flat sections and tight bends disrupting it.  For proper projects I reckon I am going to have to invest in about 20 more clamps and make the jig from MDF shaped with a jigsaw.

Conclusions:

1. Insulation is one of the key factors to building a functional steam box.  If you have to write "Caution: Hot surface" on it then you haven't insulated it enough.
2. 2x1 kiln dried pine needs about 2.5 hours of steaming if you wish to bend it to a curve with an 80 cm radius.
3. You can never have enough clamp points along the curve.  Buy more G-clamps.