All about C-Channels
There are certain things in life that you can count on: death, taxes, and of course wood movement. No matter what we try to do as woodworkers, there is no way to arrest wood movement completely. We can only do our best to reduce and manage it.
As seasons and humidity levels change, wood takes on moisture and releases it. In Southern Ontario, were I currently hang my shingle, wood takes on moisture in the warmer months and dries out over the winter. Many people think that wood movement is less of a concern because climate-controlled spaces are more common. I can assure you that it still happens, on a smaller scale mind you, but it’s still important and something to account for. If you build a piece in a shop that is not climate-controlled and it ends up living in a space that is, you will see the havoc wood movement can cause.
One of the best ways to plan for this is to understand wood movement. There are many calculators available online that will calculate the movement based on several factors. Primarily, these calculators look at the swing in humidity, the species of wood, and the type of cut (flat, rift, or quarter sawn). If you aren’t familiar with these terms and how they affect wood movement, I highly recommend adding R. Bruce Hoadley’s book “Understanding Wood” to your woodworking library. This is a helpful book that will teach you all about wood as a medium for making. I refer to mine often.
Now that I have made my case that wood movement is real in climate-controlled spaces, we need to talk about how to allow it and deal with it effectively. Like most things in woodworking, there are several options to tackle this task. In this blog post I’m going to talk about one way that I use to help keep large panels (think dining tabletop) flat. I introduce to you the C-channel.
This simple bit of metal hardware is a great way to help keep wide surfaces flat over the years. The secret behind this hardware’s success are the rolled corners. These corners, combined with the thickness of the steel, provide ample strength to help hold things flat. Elongated holes along the length allow the hardware to be secured to the wood while still allowing for the all-important movement that is going to occur.
Installation of the C-channel is simple. It involves routing two parallel dados across the width of the underside of the tabletop. You will need a minimum of two C-channels and perhaps more depending on the length of your piece. These dados should be about 25mm longer than the length of the hardware, again to allow for the wood to move. The C-channel should be secured by installing threaded inserts and machine-thread screws or bolts. The Rampa 1/4-20 inserts are a great choice because of their strength and ease of installation. You can learn more about Rampa hardware in my previous blog and video.
Another nice thing about the C-channel is that it doesn’t interfere in the aesthetic of your work. This hardware lives on the underside of the tabletop, so only the cat will see it and I’m sure Mittens will appreciate the hard work you put into keeping the table flat and true. Large slabs of wood are beautiful, but they have their limitations. The C-channel allows you to work with slab tops without the worry of serious cupping and warping. Less worry and flatter surfaces, music to my woodworking ears.