More steam bending failure

While part of the weekend was successful (the legs for the stool are fitted) the steam bending ended once again in failure.  On Saturday I finished building my PVC steam box by cutting the screw fitting off the wallpaper steamer attachment and using it to attach the hose to the pipe.  It maintains a pretty consistent 205 degrees so it seems to work well.

I finished milling by straighter grainined blanks and steamed it for an hour and 15 minutes, sure enough it splintered before the form was closed.  It did set up enough for me to at least feel how comfortable it would be against my back and I realized he curve is to steep for me.

I flattened out the curves a bit and grabbed another blank and tried again.  This time it almost made it close before a split appeared on one side.  Part of the problem is that the board is so stiff the vise does not close the form squarely which adds some extra twist.

I left the blank in the form to dry until I get back from this weeks business trip.  I’m hoping it will be a small split that I can salvage for this simple back stool.  If I can, I will finish construction and see how it feels.  I will try and use compression straps for the next one.


2 thoughts on “More steam bending failure

  1. Definitely try using a bending strap – just a steel strap along the outside of the bend to keep the neutral axis right at the edge of the wood so none of it is under tension (which is what causes those splits). Every time I’ve had a split, it’s been because the bending strap wasn’t in place and in tension (you want to watch how you clamp it in place carefully). You can take it off once the bending is complete and the jig is holding the piece in place.

    I still think the polyethylene tube idea might be worth trying, being able to take a half-hour to slowly bend the wood into shape while still keeping it hot makes it a far more forgiving process and being able to keep steaming it while it’s in the jig and bent lets most of the internal tensions subside and that reduces the springback a lot.


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