If you have never used steam to bend wood, be prepared for a near magical experience. A piece of ash that would surely shatter if bend to the radius of a handlebow or brushbow can be transformed into a pliable almost plastic material after steaming. Note however, that I called steam bending an art. It takes experience and practice to consistently produce sled parts in the shape you want. Be prepared for broken pieces and sometimes a lot of frustration. But when you have mastered steam bending, it becomes not only a practical technique but a captivating one as well.

How does steam cause wood to change from a rigid to a semi-plastic material? Wood, even when cold and dry, can be both compressed and stretched. Steam softens and plasticizes the cellulose in the woods structure. This results in an increase in the compressibility of up to 30% over the same wood when cold and dry. Steam also increases the ability of wood to stretch but only marginally (from about 1% to 2%). Once the wood is bent and allowed to cool and dry, it will largely retain its new shape although some springback (about 5 - 10%) can be expected. Therefore, build a little extra bend into your forms. Boiling water will also work but steam is more practical because larger pieces of wood can be plasticized more quickly and easily. Steamed wood also absorbs less water so it dries more quickly and can therefore be removed from the form sooner, typically after 24 hours.

Obviously, if the wood has to be held in its new shape for 24 hours, a form of some kind is necessary. Almost any material - scrap plywood or partical-board works fine - can be used to make the form. If the radius of your bends is relatively shallow (less than 12 - 15 degrees for 1 inch thick stock) then the bending can be done with a male form only. The wood can be held in place by clamps or heavy twine until it cools and dries. For tighter radii, a backing strap or matching female mold is needed to prevent the outer surface of the wood from splintering under tension (a problem called tension fracture). What is the tightest radius that a wood strip can be bent? For white ash, if everything is done just right, 1 inch stock can be bent in a 2 foot radius. Thinner stock can be bent in much tighter radii.

So far steam bending sounds great! But as with all good things, there are drawbacks. Steaming and bending wood weakens it. A strip bent to its limit and allowed to cool and dry in this shape can be 30% weaker than when straight. In a dogsled, the bent components - runners, handlebow and brushbow - are often the parts that receive the greatest stress. The question is how to overcome this weakening caused by steam-bending?

Thin layers of wood can be bent to a given radius with less loss of strength than thick layers. In conjunction with modern epoxy adhesives a laminated structure can be built with much less loss of strength. How much strength can be gained. Theoretical calculations show that the front curve of a solid ash runner 1 1/4 inches thick may be 20% weaker than the rest of the runner. The same ski laminated from 5 layers, 1/4 inches thick looses only about 5% of its strength. If laminating increases strength why not use many very thin layers? It is a question of diminishing returns. At some point, making a component out of more and more thinner layers becomes impractical. In fact, because the weakest part of the laminate is the surface layer of wood, using very thin layers may actually result in a weaker component. Epoxy is also relatively expensive so more laminates means greater cost. As a rule of thumb, plan on using strips about 1/4 inch thick for the runners and 1/8 inch to 3/16 inch thick for the handlebow and brushbow.

Not all species of wood steam bend as well as others. Generally, hardwoods bend better than softwoods. However, there are many exceptions. Mahogany, a favorite hardwood among many woodworkers, is very poor choice for steam-bending whereas white cedar, an obvious softwood, is a very good choice. Just look at the many classic cedar-strip canoes around. Fortunately, white ash, the favored woods for dogsleds, is one of the best species for steam-bending. Selecting stock for bending is easy. If it isn't absolutely clear and straight grained, dont bother even trying. Invariably, the piece will break or create a weak laminate.

What about a source of steam and an appropriate container. The only guidelines are to make sure that there is lots of steam. Other than that, almost anything goes. I've bent a few pieces of wood by steaming them in a cardboard tube put over the nozzle of a kettle. This worked fine but the tube didn't last to long. A simple wooden box made of 1 X 6s as long as the longest piece you intend to bend works well. You may need two kettles to generate enough steam for an 8 foot box (always use lots of steam) but the setup is simple, cheap and works great. Other container that I have tried are lengths of galvanized sheet metal pipe and PVC plastic pipe. While these worked well, the metal pipe had to be insulated with an old blanket to prevent it from loosing to much heat and the heat caused plastic pipe to gradually deformed until it looked like a modern sculpture. The advice here is to be creative but remember steam can cause serious burns and the wood and steam box become very hot so be careful.

So much for the basics. Now on to steaming and bending. This part is actually the shortest because remember steam-bending is mostly an art. The most often quoted rule-of-thumb is steam wood 1 hour for each inch of thickness. This is only a very general guideline. What counts more is experience. Use it as a starting point only. Each steamer and species is different. Your technique is a factor as well. Once the wood is soft remove it from the steamer and bend it is as quickly as possible before it cools. However, if you bend it to rapidly it will break. Always have extra strips on hand in case on breaks. If the curve to be bent is tight remember to use a backing form or strap and lots of steam. However, you can over-steam wood in which case it begins to turn brittle again. The most important part is practice and a feel for the wood as you bend it. Finally, be prepared for broken pieces when you first start. Be patient, when you finally get the hang of it, steam-bending really is almost magical.