5 KERF BENDING TIPS AND TRICKS! (For Beginners--Guide To Kerf Bending Wood)

Solid wood, bendy wood, pretty cool right? Making curves and wooden structures is one of those things that seems really difficult to carve between newcomers, but one particular method is actually very easy. It's called kerf bending. All it really takes is a saw and a piece of wood. So in this video I'm going to show you five tips and pointers that will have you kerf bending in no time. That's coming up next on The Honest Carpenter Show. Kerf bending is the process of removing small thin sections from a piece of material until it loses its rigidness and becomes flexible. And this process works for all sorts of building materials, from wood and plywood to MDF and even vinyl products. So how do you actually do it? If you watch my video about the most important word in carpentry, you know that kerf refers to the slot or groove that's left behind when a blade passes through a piece of stock. So in kerf bending we're using the natural width of a saw blade, what's also called a kerf, to leave a patterned series of cuts in a board. But we make sure that those cuts don't pass all the way through the board. You want to leave a thin layer of uncut material on one face to act as a ligament to still hold the piece together. So the missing spaces give it flexibility, but the uncut surface keeps it all intact. Let's get into some pointers about how to do this effectively. Tip number one, use an appropriate cut depth. What is the appropriate cut depth? Honestly, it can vary by material because different materials have different pliability. For instance, PVC may be more inclined to flex than say a hardwood like oak. But whatever material you're using, a lot of the same rules apply for each. For instance, if you don't cut deeply enough on a piece, you won't overcome the material's rigidity. This can cause the piece to not bend effectively. It's too stiff. But if you do cut too deeply, the remaining material will lack strength and it might just tear or shred as you handle it. So you want to cut just enough but not go too far. I like to use plywood as a metric because it shows its layers on the edge. For many plywoods, I'll leave something like one and a half layers uncut. This translates to just shy of an eighth of an inch. That depth is going to work well for most materials. So you can set your saw blade height or cut depth by eye to that point. But before you carry out the entire process, you want to make sure that that depth is going to work, which brings us to tip number two. Always test on scrap. Whatever material you're going to be curve bending, do yourself a favor. Set aside a small piece to experiment on or two small pieces to experiment on. Try a deeper cut on one board versus a shallower cut on the other. See which one flexes the best and really try to break the piece. Be rough with it. It's a stress test to avoid problems later on. This is really important if the stock you're using is a nice hardwood or an expensive product. You want to know your parameters before you move on to the real thing because curve bending basically destroys a piece of lumber. You're never going to be able to put material back in. You've just got to start over again at that point. So be sure to use test stock. Tip number three. Spacing matters. Getting a piece to bend really isn't that tricky overall. You just put a bunch of curves in it at 90 degrees. But controlling or predicting the bend has to do with how you space those curves. Cuts placed closely together, say just one blade width apart, will produce a tighter radius. But cuts spaced farther apart will produce a shallower curve. There's a lot of math involved with figuring out proper curve spacing. It has to do with the thickness of the material, the width of the blade, the span of the curved section. It's confusing and I'm not good enough at math to bother with it. Fortunately there are curve spacing calculators online these days. You just enter your values into those and it'll kick out the numbers you need. Once you know your desired spacing, you can make the cut passes on your board at the proper marks and the board flexes to the radius you want. Now you have to know how to make it hold that curve even once you let go. Which brings us to tip number four. Setting the shape. This is really two tips because there are really two ways of doing this. The first one is to just glue the curves shut. And this only works if you plan on having the board fully curved, which means you have to have done your math right so that the radius winds up where you want it to be. If it is, you can just lightly fill the curve cuts with glue, then bend the board to close them, clean up the excess, and let the glue dry. When the glue is set, the board will hold that shape and it'll be really strong. I've seen differing opinions on what kind of glue to use here. Everything from construction adhesive to Gorilla Glue, but I've always just used Titebond 2 as long the material is wood based. It's plenty strong, it runs into the curves, and it cleans up easily. It's really my glue of choice in the shop. But the second way of setting the shape doesn't even involve glue. Instead, you use another piece of material to fasten onto your curved piece to hold it in place. I did this on a short notice project a few years back where I had to make these portable wooden platforms for a broadcast. They looked like pianos when you broke them down because they had to fit into vans so that you can move them to the job site. Here I curve bent the 2x6s that acted as joists. You can see the cuts in the radius. But then I used subfloor pieces to hold the curves in the shapes that I wanted. I just fastened down through the subfloor with screws, making sure to hit solid wood between cuts. And the cool thing about this is I didn't even have to calculate curve spacing. I just needed roughly the right number of cuts to get enough bend. Then I cut the subfloor into the shape I wanted and made the joist bend match the subfloor. This isn't quite as strong as laminate bending where you layer up multiple pieces of wood, something I'll talk about in another video, but it was plenty strong enough here and you can do it on a much smaller scale too for like woodworking projects. On that note, for the fifth pointer, I'll say that you don't always have to bend a curved board inwards. You can also bend it outwards. You just have to be more careful when you do it. You probably want to make sure these curves are hidden inside a project. You see this a lot in guitars for instance, and you want to make sure you don't snap your piece when bending it. You can sometimes saturate it with a little water or even steam it over a pot on the stove for a little while. This will increase the moisture content in the wood and it'll make the wood more pliable and flexible while you're working with it. And remember, you can really make your curves in a lot of different ways. I did mine here carefully with just the miter saw. If you have access to a radial arm saw, that can work and there are plenty of ways to do it on a table saw even without a crosscut sled. I've done it lots of times with nothing but a circular saw and a speed square. Just make sure to set your depth accurately, keep the cuts at 90 degrees, and be sure the blade travels all the way through the cut on each pass. That's really all there is to curve bending. And of course, please be careful and always practice safety precautions. What do you think? Do you have anything to add that I didn't mention? Do you have some trick that I don't use? Please put it down in the comments. Also, I've got some newer t-shirts for sale these days. They're right above the comment section below the video. Check them out down there if you're interested. And of course, please consider subscribing and hitting that little bell to turn on notifications. That way you'll know the moment we post a video. I'm Ethan James with TheHonestCarpenter.com. See you next time.