Question
This is my first time bending wood. I am building a steam tube of PVC pipe. Caps on both ends, steam vent on far end. Going to use a metal can and turkey fryer gas cooking element, run a tube in the end with a removable cap. The research that I have done says to soak the lumber in water for a day and then steam for one hour per inch of thickness. I am going to do some practice runs with poplar, but am going to use walnut for final curve. Am I on the right track?
Forum Responses
(Furniture Making Forum)
From contributor K:
Don't waste your time on the poplar - I don't think it is a good one for steam bending. I would also forget the soak cycle. Use air-less-than-dried lumber if you can get it. Most important is to use compression straps. Lee Valley has a free publication with good info.
Riven air-dried walnut will bend the best. For sawn lumber you really should have a jig that utilizes a strap on the outside of the bend and ideally traps the ends of the bending stock. Soak - no! Don't be afraid to steam longer than minimum times, and practice with walnut.
I insulate both by wrapping them with several wraps of some 1/8" packing foam. It is easy to do, and anything that I can do to improve the chance for success is worthwhile. I drilled a little hole in the far end of my tube chamber for a thermometer. I have forgotten how much rise in temperature I got from insulating, but it sure helped. Five or ten degrees off of the top is enough to cause failure.
I use a 1300 watt electric hot plate to heat an old ~1.5 gallon pot with a sheet metal lid welded on. I then cut a hole in the sheet metal lid and welded a 1.25" pipe nipple to it. I drilled a hole in the bottom of the plywood box and screwed a 1.25" pipe flange with a 2" long nipple over the hole. If you don't want to weld, it would work just as well with a tea kettle, you would just have less water capacity. I had some flexible PVC (for hot tubs) that I used between the two nipples, but radiator hose would be a better choice. My access lid just fits snug so excess pressure can escape and the steam can move through the box. I put 5/16" dowels across the bottom about every 8" so that the work piece doesn't sit on the bottom of the box, which would prevent that edge from being steamed.
I set the box on a table so that it slants down toward the steam inlet with the flange hanging over the end of the table. With the burner on the ground, the re-condensed water runs back into the pot and is recycled. Theoretically, if no steam escaped the box, you would be able to run the closed system indefinitely without running out of water. Obviously steam does escape and the plywood absorbs some water, but even still, it will provide plenty of steam for definitely more than three hours (I have no idea how long it runs, but I know I've run it for 3 hours straight) with a lot less energy than heating 5 gallons would require. When I have to refill the water I usually just dump it down the open end of the box and let it run into the pot. When I'm done I leave the lid open so the plywood can dry out. Sometimes some mold will form on the inside but it turns out that steam is a great way to kill mold.
I purchased the hot plate from Meijers for $9.99. It has a spiral burner just like an electric stove. It still amazes me that it's possible just to manufacture them for ten bucks, never mind shipping it to the states and generating any profit. It takes probably 15-20 minutes this time of year before the water gets to a full boil. I'm sure that's longer than a propane burner would take, but I think that am few extra minutes of pre-heating is definitely worth the convenience of electric power.
I have very little money in my setup, it works well, and sometimes it's fun to build something that you can just recklessly nail together.
The moisture is definitely a critical element in the bending. If you think you only need heat, trying using an oven and let me know how much success you have. Heck, if it does work, please do let me know so I don't waste any more effort on steam boxes.
I've also heard before that you should soak kiln dried wood in a water/fabric softener solution before bending. I've never tried that but always figured I could pull it out of the bag of tricks as a last resort if my plans called for bending more than my lumber is limber enough to handle. I suppose it makes sense that the fabric softener would leave the cellulose in wood more pliable the same way it softens cellulose in cotton. I've also heard that fabric softener is a good lubricant but I'm a little surprised that it makes a difference when added to the steaming because I'm pretty sure that the active ingredients are rather hydrophobic.
My biggest secret to success has been building good forms. I try to build the form with an outside radius which assures the radius stays uniform throughout the piece while you're applying the bend. If you bend the piece into an inside radius form, the piece being bent tends to fold in one place and that's an easy way to crack it.
Obviously when you bend the wood, the outside face becomes longer than the inside face. The point of the straps is to keep the outside edge from stretching so that the inside edge is forced to compress. Wood is better at compressing than stretching, so if you keep the outside edge from stretching and tearing, you should be able to apply more bend without cracking.
I use the 1 hour/1" thickness rule-of-thumb for a starting point, but I usually forget what time I put the wood in anyway. I've heard you can overcook and make the wood more brittle, but I've never experienced that problem.
Another important thing to remember is that it's almost impossible to bend the last couple inches on either end of the board. If you need curve throughout the length of the board, cut it long, bend it, and then cut it to length. Also remember that if you're not laminating multiple pieces together, you need to account for pretty substantial springback.
I went into my first wood bending project thinking it would be way harder than it was. The actual bending of the wood isn't very difficult. However, cutting, joining, sanding, routing and everything else gets much more complicated now that your work piece is curved. As such, radius projects are a great way to challenge yourself and improve your skills. However, if you want to make money, wacky wood and veneer is the way to go.
