Solving the Steamy Mystery

(or Why Are You So Bent Out of Shape?)
 

by Sherwood Heggen

Steaming-bending wood has always been somewhat of a mystery for many. Hopefully, some light can be shed on the process by this article to allow more amateur restorers to use it. All of the questions and answers won’t be addressed, but it will be a starting point for the curious about the Steamy Mystery of bending wood.

Why would it be necessary to steam bend wood when restoring a boat? Take a look at some of the parts as to how they twist and bend. Anytime a wooden part must be bent or forced into a new shape without cracking or breaking it, the process of steaming-bending becomes necessary. A chine, for example, is a curved piece that is not sawed to that shape. Rather, it is bent into that shape by the process of steam-bending. This provides for greater strength because there is no short grain at the end of the piece. Parts that fall under this category include ribs for canoes and lapstrake boats, transom bases, fore and aft shear planks, etc.

How does the exposure of steam to wood allow the process of steam-bending to work? A source of information on steam-bending that came off the Internet described it as follows: “What you are doing when you are steaming wood for bending is softening the hemicelluloses. The celluloses are polymers that behave the same as plastic resins.” So, there you have it. The mystery is over. Actually, the mystery has just begun.

There is so much to learn about steam-bending that no simple statement will tell you enough. The equipment required to steam bend wood can be very basic. Jerry Klopp, whose Century Sea Maid project was featured in the latest Gadgets and Kinks, has provided a picture of his steamer with which he bent some oak. In the picture you will see an electric hot plate, a metal pail with a lid on it, some hose wrapped with insulation connected between the lid and the box, and a steam box on a stand to raise it above the steam source. This set up is barely adequate for anything bigger than small parts such as canoe or lapstrake ribs according to Jerry. To steam bend chines and transom bases, a bigger heat source is necessary. Jerry substituted an LP gas burner for the hot plate. It brought the pail of water to a boil in a hurry and gave all the steam necessary to do his transom base and chines. The steam box can be of any size or shape to accommodate the part. Proper size would be a little larger than the part itself to allow steam to circulate about the part suspended somehow inside. The box can be made of a variety of materials to include, but not limited to, pine, rigid foam insulation, metal foil insulation, PVC pipe, and double wall metal chimney pipe. The object of the “box” is to retain heat generated by the steam. It is advisable to allow the steam system to breathe by letting the steam escape from the box to some degree. This assures there is always fresh hot steam coming from the boiler allowing the box to get up to maximum temperature inside. Temperature of the box should be monitored with a candy thermometer to assure a temperature of about 212 degrees. Be sure to allow an outlet at the bottom of the box for condensation to drip out. Steaming the part is only half of steam-bending. The steamed part needs to be bent and caused to hold its new shape. Here is how.

Preparation of a form is necessary to hold the part’s new shape until cool. Take a look at Jerry’s set up for clamping the part in its new shape. The shape is determined and a little extra bend is allowed for some spring back when the part is removed from the form. Be prepared with all of the necessary clamps and place the form in a comfortable working position. Also, have ready a pair of heavy rubber gloves, not cloth gloves. The wood will be very hot and wet. It is time to cook wood. Turn on the boiler and get the box steaming. Quickly open one end of the “box” and place your wood piece inside. Now cook at 212 degrees for one hour per inch of thickness, as a rule of thumb. It could be more or less depending on many variables. It is a good idea to include a sacrifice piece to take out first and test by bending to see if the real piece is ready.

When the time is up, remove the part and very quickly, like in seconds, slam it into the form and clamp it before it begins to cool. Leave the part in the form until it is thoroughly cooled, preferably until the next day. When you remove the clamps, the piece will retain its new shape with usually only a little spring back. Sounds quite simple doesn’t it? Actually it is.

It is evident there is much more to steam-bending wood than this, but those are the basics. There actually is a lot of information out there on the subject but you need to do a little hunting. Some suggestions and references are: Search the Internet on the subject of woodworking. The Chris Craft Club has a chat page where the topic is discussed. Wooden Boat and Classic Boating both have had articles that discussed the subject to various degrees. Order back issues. Two books available through Barnes and Noble are Understanding Wood by R Bruce Hoadley and Fine Woodworking on Bending Wood. Both are published by Taunton Press. Perhaps the most informative of all will be the BSLOL Workshop on March 14, 1999 at Dan Nelson’s shop. There you will see live demos of this fascinating process. Time and place are described elsewhere in this issue of the Boathouse. Don’t miss this one. It is gonna be interesting. All of your friends will be there and you are going to learn something!