Replies

1. 
   hammer1 | May 15, 2005 05:15pm | #1

   I made a steam box out of a piece of PVC plumbing pipe. The key in steaming is to generate a thick, hot and consistent amount of steam. Wall paper steamers don't have enough power to fill and maintain a large box. A 3-5 gal. can will hold enough water to keep it going, it's nice to be able to add water without interrupting the steam flow. I use some electric kettles to boil the water before adding. The wood will lose it's elasticity within seconds so you have to be prepared to start bending immediately out of the box. Be careful around steam, wear gloves and a face mask, it can burn you badly.

   I used 4" schedule 40, drilled a 1/4" hole at one end and used a piece of aluminum soffit vent, to keep the wood elevated off the pipe and out of the condensation. The PVC will deform from the heat, lighter gauge PVC will really deform. Don't be afraid to let the pieces steam long enough to get them very pliable. The 1hr/inch rule is a little short from my experience. You need a good, fast operating form to make consistent bends. The pieces will shrink a little as they dry out, don't try to glue them in place while they are still wet.

   Beat it to fit / Paint it to match

   
2. 
   KeithNewton | May 15, 2005 07:37pm | #2

   Good advice above. I would like to add, that there should be a small drain hole in the bottom of both end caps, and insulation would help keep the heat in better than the pipe alone, especially on a cold day.

   The idea is to get the wood to 212 degrees, at which point the lignin softens, and allows a little slipping between the cells. If your steam-box conducts the heat away too rapidly, it will take longer to the wood to that level all of the way through.

   If you are getting steam rather than water out of the drains you should be OK.
   You may already know that you should not be using KD lumber. It should be around 18 %.

   Too much heat for too long, can cause brashness, which is a defect that can not be seen, but can lead to a wood that would normally have good elasticity to break abruptly.

   Oh, one other thing, I believe you mentioned that this would be for trim. Trim that has an asymmetrical shape like a thick side and a thin side will want to roll or twist badly, and something like crown will just want to flip onto its back.

   If you have not read any books on the subject, Lee Valley tools has an excellent book which can be downloaded free. Start here. http://www.leevalley.com/wood/page.aspx?c=1&cat=1&p=45866

1. 
   micr03 | May 15, 2005 08:40pm | #3

   Thanks For All Your Help! I Think I have enough information to go on now I will let you know how it goes. Woodworker I.

1. 
   KayakGreg | May 17, 2005 12:00am | #4

   Something to add to some good advice you have already received. If you pre-soak the wood you can cut down on the steam time. I have built several skin-on-frame kayaks with a real experienced mentor, who has built around 400 boats in the last dozen years. His technique is to pre-soak white oak ribs, 1/4" by 1 1/4", for about a week. His equipment is a Coleman stove with a big old pot feeding near one end of an aluminum downspout. The other end, slightly elevated to cause the condensate to run back to the source, has a canvas flap over it to keep the steam in. The ribs are suspended on threaded rods that hold them off the bottom. Steam time is 3 minutes, work time is one minute tops. This allows the rib to take pretty sharp bends and still stay straight where you want it to. They are then retained in mortices in the frame to avoid springback as they take a set, similar to using a form. If the wood is steamed too long, it will act like a wet noodle, which may be okay if you are going to retain it in some type of sandwich form.

   By soaking, you are recreating to some degree the conditions found in green wood. The steam will penetrate the fibers much more quickly if there is already moisture there to act as a pathway. If you have ever picked up a very hot pan with a wet dishtowel you know what I mean. The heat will migrate to your skin much faster than if you use a dry dishtowel.

   Greg  

1. 
   micr03 | May 17, 2005 03:26am | #5

   Thanks for the info Greg. It all makes sense.