This article was updated on 03/14/19. Happy National Pi Day!
If it was an ideal world, you could always nail wooden molding to a straight wall. Alas, this is not the case, particularly with wood-stud framed walls. But often, in other situations, you need for it to follow a particular curve or architectural radius.
As an example, have you ever had to nail trim to the railing of a circular staircase, or framed an ornate mirror, or wrestled with trimming out curved wood window frames? If you find yourself in one of these situations, your wood needs to conform. This article explains two ways to bend wood molding.
Wood is a Renewable Architectural Resource
Wood has been harvested and milled for architectural use since construction on a higher level than “primitive” began. Initially it wasn’t bent at all, but just crafted into the desired shape. Remember the old joke about the guy sculpting an elephant? “I just chip away everything that doesn’t look like an elephant.”
The obvious downside of this method of crafting it was that wood grain’s integrity became compromised and the final result was a complete loss of the timber’s overall strength. Plus, a lot of wood goes to waste; it is something you do not want when working with expensive stock.
But remember, when wood is bent, or coaxed might be a better word, maintaining the material’s structure and the continuity of the grain, the timber’s strength is actually increased in most situations.
How to Use a Steam Chamber to Shape Wood Molding
Perhaps the best way to make wood conform to the shape you want is to infuse it with steam. This is called the steam bending method. All wood is far more malleable when immersed in a humidity moisture bath.
The basic idea with this approach is to apply hot steam to the material until it’s workable first. Next, it’s removed from the PVC steam heat chamber. The next step is to clamp into the desired architectural shape. Finally, allow it to dry to ambient humidity conditions. For this, you will need an area in your wood shop where it will not be disturbed.
Making the Steam Chamber
This shop set-up is easy using modern materials; it would have been much more difficult for carpenters of old. What you need to start with is a length of PVC pipe that’s long enough for your material. It should also be of the correct diameter to accommodate your material.
Allow about a foot extra for the length. You’ll also need 2 PVC pipe end caps. You’ll assemble all this into your very own steam chamber. Drill a tiny hole in the center of each pipe cap.
Note: While you’re at it, why not make it really big? You never know when you’ll need it again! (Disclaimer: I’m from Texas; everything’s bigger in Texas!
Turning Up the Steam!
First, insert your trim into your steam chamber. Next, attach a source of steam to the hole in the cap on one end. What can you use for this? It can be just as simple as a length of plastic or latex surgical tube that you’ve attached to your tea kettle and your DIY chamber.
The small hole on the opposite end of your chamber needs to be sealed just until your chamber is completely saturated. After that, some of the steam may be released allowing new, hotter steam to replace it.
Introduce new steam as needed. Heat + steam = soft, pliable wood trim. When it is soft enough to work into the needed shape, remove it from the PVC chamber. Bend it into the desired shape and allow it to dry out. There are many ways to maintain the bent shape until it is dried. Nails partially driven into plywood can be used to this end. Use a moisture meter to determine when the wood is dry enough.
Bending Molding Using the Back-Cutting Method
There are many times when your molding’s opposite side won’t be seen on your final woodworking project. This is where back cutting is a great candidate solution. This will involve cutting a number of tiny V-shapes in the trim stock.
This is usually best done using a coping saw since the blade is thin and surgeon-like control is available. This will allow the trim to gradually take on the proper arc. The notches need to be as equally spaced and close together as possible.
The tighter your curve needs to be, the nearer together the cuts will be. The critical things to keep in mind when bending molding is to maintain patience and persuade the
wood, not force it.
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About the author:
Kelly R. Smith was a commercial carpenter for 20 years before returning to night school at the University of Houston where he earned a Bachelor’s Degree in Computer Science. After working at NASA for a few years, he went on to develop software for the transportation and financial and energy trading industries. He has been writing, in one capacity or another, since he could hold a pencil. As a freelance writer now, he specializes in producing articles and blog content for a variety of clients. His personal blog is at I Can Fix Up My Home Blog where he muses on many different topics.
Kelly R. Smith was a commercial carpenter for 20 years before returning to night school at the University of Houston where he earned a Bachelor’s Degree in Computer Science. After working at NASA for a few years, he went on to develop software for the transportation and financial and energy trading industries. He has been writing, in one capacity or another, since he could hold a pencil. As a freelance writer now, he specializes in producing articles and blog content for a variety of clients. His personal blog is at 
