Bending Wood Molding in Your Wood Shop
Make Wooden Trim Conform Using Steam or Back-Cutting for Woodworking Projects
© 2009 by Kelly Smith all rights reserved
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. And in other situations, you want it
to follow a particular curve or architectural radius.
For 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 wood window frames? If you find yourself in one
of these situations, your wood needs to conform. This article explains two ways to form wood molding.
Wood, 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.
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.
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
Possibly the best way to make wood conform to the desired shape is to infuse it with steam. This is
referred to as the steam bending method. All wood is far more mallable when immersed in a moisture bath.
The basic idea 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.
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'll need first is a chunk 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.
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 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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