The Ultimate Steam Box was developed by Mike Dunbar of The Windsor Institute and all credit for the ideas expressed in this article are taken from both the actual use of Mike’s ideas and his newsletters, known as the Windsor Chronicles. They may or may not be significantly more energy-efficient; boiling water takes the same amount of energy no matter how you do it, so the only question is how much energy gets lost to the environment rather than going into the water and being kept in the steam. BPT # 9 (or Primitive Technology – a Book of Earth Skills) has a couple of set ups for steaming boxes within the article Bent Corner Box Making, by Greg Blomberg (page 47 in BPT #9).
I don’t know about chemicals, But, soaking the wood in cold water overnight and then wrapping the wood in mattress pads and dousing it with boiling water and letting steep for 20 minutes works to get you most of what steaming will get you. Others uses include straightening blowguns, recurving and reflexing bows, bending basket rim sticks, net hoops and looped stirring sticks, bending curfed wooden boxes, and shaping dugout canoes. I placed the steamer on the plywood and the steam box above, as well as a bucket for drainage.
With steam-bending, I can procure my stock from a straight-grained log with a wedge and a froe, shape it with a drawknife, and bend it with a steaming rig that I built using a few simple items from the hardware store (look for a post on my steam-bending rig before too long, though there’s plenty of information on the web. Also included are the key topics of moisture content, wood preparation and elasticity, steaming and other softening treatments, and working with laminates and adhesives.
All the necessary tools and equipment are discussed with an eye to budget and practicality, making this appeal to both amateur and professionals of all skill levels. Guitars, furniture, even canoes’?bending wood adds a new dimension to what can be built in a workshop. Lots of attention to controlled drying of bending stock after it’s been shaped to prevent checking especially on large bending stock. Stock preparation for bending is no different than any other woodworking project.
Greenwood, which has a moist composition, is the standard recommendation for steaming and bending, though different applications require hardwood selection. We decided to make the bent wood ribs of our replica Wright gliders by laminating the parts with a water-resistant aliphatic resin (yellow) glue. Steam bending is also a low energy and ecological method of manipulating wood with no nasty glues and very low levels of wastage. Rattan superficially resembles bamboo and is the palm wood most suitable for steaming and bending.
Short grain is where the grain of the wood travels across the width of a curved piece of wood instead of following the curve. Use the power of steam with the Earlex Steam Generator to create new furniture designs and woodworking projects with bended wood. Air-dried wood is ideal, and the bend is most likely to be successful if the wood is near the fiber saturation point (25-30%).
There are many ways to steam wood, but I’m going to talk about what is the safest and easiest way I have seen to do it. Here at the Infinity Tools shop, we carry the Earlex Steam Generator This simple device is basically a wallpaper steamer with a very nice brass steam box adaptor. Bending compound curves, as in a looped stirring stick, or simple rims when there is a weak spot are aided by the use of forms, which can be as simple as a chunk of wood and some cordage (see illustration). But I think anyone can do it, if they are willing to spend the time and money to achieve the knowledge, and build the appropriate equip’t to do so.
A long time ago, I knew a wood turning craftsman who created works both beautiful and unique. This unit is not only extremely easy to setup and use, it allows up to 2 hours of steam which is more than enough for most bending projects. The grain on figured wood doesn’t run the length of the piece, but runs alternately up and down through it. Over-wetting this wood can cause the grain fibers to separate from each other, which results in fractures.
Additional results included time to temperature, rate of moisture content change, final moisture contents, specific gravity influence. Use a permanent marker, and choose a surface that can withstand repeated contact with the wet wood. Grip the Side Bending Strap and the wet wood together between the heel and fingers of each hand to help keep the wood flat against the bender. The steam is simply a very efficient carrier of heat, and it has the added benefit of being the right temperature. It can also be used in furniture making and wood craft work for making things such as chair back slats and wooden utensils.
Using Schedule 80 PVC pipe and fittings, the pipe is impervious to steam heat, will not absorb water and will dry quickly, ready for storage in a few minutes. Take each peice out and put it in your bending jig (I use a metal strap backing made from plumbers metal tape with foam backed tape on it), and push on it as far as it will go, and than put it back in the water and take the next peice, repeat. Fill the water tank with water; (image 2) The tank must be filled sufficiently to allow the steam process to be maintained for a sufficient length of time. I assume this acts to harden the wood against future compression failure (the tines tend to break above this scorched bend).
Preparing the wood was made easy by running strips of oak through the thickness planer. Alternatives to steambending – You may not need to use steam to bend ribs or other framing members. PVA glues have a tendency to creep over time and wouldn’t be my first choice for bent lamination. Steam is the best way to go for most boat applications because what you want is something that is strong and not just decorative. The box needs to be large enough to hold the wood you want to steam, but not so large as to require an impossible amount of steam. In this way the tops of the laths form a smooth line which shall be the determining factor for bending the steamed ribs.
Wearing heavy work gloves, remove the softened wood from the steam bath and start bending it around the form. The ‘hot pipe’ is an effective method of heating thinner strips of wood for bending. If you’re not sure of the clamp time, wait a full day before you remove the assembly from the bending form. The steam box should be long enough to hold the length needed and the length needed should be longer than the curve. For larger wood projects, this unit is too small and does not produce sufficient heat.
I didn’t waste any time researching things that would tell me I couldn’t do it, like studying what lignin is. I did however find an old Woodwright’s shop episode were Roy Underhill showed how to use a metal strap during the bending process to compress the outer fibers, preventing them from splintering. Cut the length of your wood strips to be a little longer than your necessary final measurement.
It was a 360 degree bend, and the benefit you get from steaming is very short lived, so I had to apply the steam directly to the wood strips while bending at first without glue in order to get them around some of the sharp corners. Lengths appropriate per drum size, scarf joints and jigs to cut them, then the forms to bend the wood to, need to be created.
Wood fibers compress much more easily than they stretch, which is why the most common failure when bending wood is splitting on the outside of the curve. I steamed the laminations for these rocking horses with an Earlex steam box, but they are all thin strips. You can’t soak the wood as thoroughly as with straight-grained pieces, and everything happens a lot faster.
A flat piece of wood when bent can normally absorb a difference between outside and inside radius of 2 to 3% (without using end pressure or steaming) before breaking. To solve this problem, they eventually abandoned steam bending for an early form of cold bending. I should mention at this time, however, that steaming does cause an overall loss in strength after the piece is dried, so we do want to keep the steaming time to a necessary minimum.